Springtime on a farm is typically filled with the hustle and bustle of gearing up for planting season. This is the time of year when most farmers focus on de-winterizing the sprayer, changing oil in the tractors and checking the seed meters on the planter. If you use a field cultivator, it is also important to make sure it is properly adjusted to help provide a uniform seedbed for the upcoming planting season. Whether this is the first season or the thirtieth season for the field cultivator, there are a few items to check before making your way to the field this spring. While field cultivators are specifically discussed here, many of these concepts also apply to other spring tillage tools (vertical till equipment, etc.).Fore and aft leveling of the tool
There are several questions to consider before heading to the field. Is this the first season using the tillage tool with this tractor? Were new tires put on last fall? Has ballast been added or removed from the tractor since last season? Any of these modifications could affect the height of the tractor’s drawbar. Knowing the relationship of the tractor’s drawbar to the implement is essential to making sure all ground engaging sweeps are tilling at the same depth along the length of the machine. Improper pitch of the field cultivator can cause uneven loading of the front or rear sweeps when pulled through the soil (Figure 1). Inconsistent soil interaction between sweeps can decrease the cultivator’s ability to follow the contours of the ground.
Figure 1: The field cultivator pictured is not properly leveled due to the rearward pitch. This will cause the rear sweeps to till deeper than the front sweeps creating an uneven seedbed and improperly loading the tillage tool. (photo modified from deere.com to represent a non-level field cultivator)
With the field cultivator properly attached to the tractor, a relativity simple procedure can check the fore and aft pitch and the lateral roll of the implement.
- With the tillage tractor attached, completely unfold the field cultivator and park it on a flat level surface (preferably concrete or a well-leveled gravel lot).
- Using the hydraulic raise/lower function, lower the cultivator until the tips of the front rank of sweeps are approximately three inches from the ground.
- Using a tape measure, record the distance from the tip of sweep to the surface of the ground on the front rank of sweeps.
- Conduct this measurement every 10 inches or at every fold section of the cultivator. This helps check levelness across the width of the machine.
- Repeat the measurement process for the back rank of sweeps.
- If the values for the front and rear ranks are not within one inch of each other, adjust the connection linkages of the field cultivator using the manufacturer’s recommendation to adjust the fore/aft pitch of the machine. If you noticed height differences when measuring across the width of the machine (lateral roll), then adjust your wing/section linkages to level the machine across its width. Some variation will naturally exist within each shank/sweep, so concentrate on identifying large differences or trends in height differences across the machine.
Correct implement tire pressure is essential to ensuring high job quality of the tillage tool. Due to the standard parabolic shape of a field cultivator, the forces of the ground-engaging sweeps are constantly pulling the tool deeper and deeper into the soil. The implement’s tires play a critical role in keeping the field cultivator operating at a consistent depth. Over- or under-inflation of the tires can cause the cultivator to run deeper or shallower. This creates not only an uneven seedbed for the planter but gaps in the sweeps, potentially causing weed escapes. Operating at the proper inflation pressure also ensures the compaction caused by the machine is minimal. The implement’s road tires carry the weight of the frame while on the road and in the field, and may need to be set at a higher pressure than the tires on the wings of the tool.
A level soil surface and subsurface is important for establishing a uniform seedbed for the planter to ride on. Inconsistency in the tillage operation can lead to poor singulation, improper seeding depth and poor or uneven emergence. Taking extra time to check over the field cultivator in the spring can potentially lead to a decrease in fuel consumption, an increase in yield and an overall smooth spring planting season.Authors’ note
Working on farm equipment often requires the operator to climb over or under tractors and implements to maintain and service them. Safety is critical for all farming operations, but especially for machine maintenance and preparation. Before working on any equipment, follow the proper safety procedures listed in your owner’s manual.Category: Equipment and MachineryTags: spring field operationfield cultivatorEquipmentsoil preparationtillagetire pressure
With the critical need for respirators and other personal protective equipment (PPE) for health care, there is a potential shortage of PPE, particularly N95 respirators, in the marketplace for agriculture and pesticide applications.
The pesticide label lists the required PPE. See “Wear PPE When Using Pesticides” for more information. Applicators who do not follow the label-specified PPE requirements because of lack of access to a respirator or other PPE put themselves at risk, potentially add to the need for medical care, and are in violation of the label. The Environmental Protection Agency (EPA) has made no exemption or relaxation of PPE requirements.Review Pesticide Labels
Review the labels of products that are key to your agricultural commodities. Some herbicide, fungicide, and insecticide labels require N95 or other types of respirators to protect from exposure. Remember, all respirators, including N95 filtering face-piece respirators, require fit-testing, training, and medical evaluations. See “Using a Pesticide that Requires a Respirator?” for additional information.Inventory PPE
Create a list of the PPE you currently have on-hand, including gloves, coveralls, eyewear, and respirators. Carefully assess that you have enough PPE for critical pesticide applications. Extra PPE can be donated to health care workers by contacting your local County Coordinator for Homeland Security and Emergency Management.What if the Label-Required Respirator is Unavailable?
For pesticide products that require a respirator, look for an alternative product (not requiring a respirator) or management method. There may be a product with the same active ingredient, but the formulation type reduces the need for respiratory protection.
Unfortunately, the only way to query alternative products is to review their labels. The following websites can be used to search for products registered for use in Iowa:
See also “Pesticide label references available online!” for more information on accessing labels online.Category: Pesticide EducationTags: PPEpesticide applicationrespiratorspesticide labels
Fertilization is just as important for forages as it is for row crops to maximize productivity. This article addresses spring fertilization considerations for forage crops and pastures.Nitrogen considerations
Nitrogen (N) applications can either be a one-time, annual application or can be split applied. Suggested N application rates for single application are in Table 1 and rates for split applications are in Table 2.
Table 1. Suggested N application rates for a single annual application
April: 60-100 lbs N/acre
Tall cool-season grasses
April: 80-120 lbs N/acre
Late April to early May: 80-150 lbs N/acre
Table 2. Suggested N application rates for split applications
- Early spring (March-April) 60-80 lbs N/acre
- Late spring (May-early June) additional 30-40 lbs N/acre (optional)
- And/or late summer (August-September) additional 30-40 lbs N/acre
Tall cool-season grasses
(orchardgrass, smooth bromegrass, reed canarygrass, and tall fescue*)
- Early spring (March-April): 80-120 lbs N/acre
- Late spring (May-early June) additional 40-60 lbs N/acre (optional)
- And/or late summer (August-September) additional 40-60 lbs N/acre
* Note: For pastures or hayfields with tall fescue, high N rates increase the risk of fescue toxicosis.
For legume-grass mixed pastures or hayfields, if the stand is less than 1/3 legume, treat as a grass pasture or hayfield. If the stand is more than 1/3 legume, no nitrogen is recommended. Also note that for legume-grass mixed pastures or hayfields, high or frequent applications of N (particularly spring N applications) will make the grass component more competitive and limit the amount of legumes in the mixture. To encourage a greater legume presence, use modest N rates and limit application to summer or fall.Phosphorus, potassium, and lime considerations
Forage plants also respond to added phosphorus (P) and potassium (K) when soils have low or very low P and K test levels. Taking a soil test is the only way to know what those levels are and to determine how much P and K is needed.
While pastures typically have little nutrient removal, that doesn’t mean that the redistribution of those nutrients is equal. Nutrient levels tend to be higher near shade and watering sites. Additionally, how grazing is managed (continuously, rotational, strip, etc.) can impact nutrient redistribution. Taking these factors into account when soil sampling pastures is important.
For hayfields or pastures that have hay removed, it is important to put on additional P and K fertilizer based on crop nutrient removal. For instance, each ton of smooth bromegrass hay harvested at 15% moisture removes 7.9 pounds of phosphate (P2O5) and 41 pounds of potash (K2O) per acre. More information on crop nutrient removal for other forage crops can be found in Table 3 of PM1688, A General Guide for Crop Nutrient and Limestone Recommendations in Iowa.
Timing of P and K applications can be flexible; however, it may be more convenient to fertilize in the fall or spring along with the N fertilizer application.
Soil pH can also impact forage productivity. It is recommended for grass-based hayfields and pastures to maintain a soil pH of around 6.0. To encourage and maintain legumes, try to maintain a pH of 6.5 for clovers and birdsfoot trefoil and a pH of 6.9 for alfalfa.Additional resources
- Fertilizing Pasture (PM 0869)
- A General Guide for Crop Nutrient and Limestone Recommendations in Iowa Decisions (PM 1688)
- Take a Good Soil Sample to Help Make Good Fertilizer (CROP 3108)
The Iowa Department of Agriculture and Land Stewardship (IDALS) has waived the deadline for pesticide applicators to meet recertification requirements, following a proclamation by Iowa Gov. Kim Reynolds March 22.
The waiver allows Iowa pesticide applicators who were certified as of Dec. 31, 2019, to retain their status through Dec. 31, 2020, and temporarily allows commercial certified pesticide applicators to continue to operate under a current company license without having to immediately submit proof of training or testing.
Applicators still need to meet pesticide certification standards by Dec. 31, 2020. In-person examinations required to renew a pesticide applicator certification must be completed by Dec. 31, 2020. All pesticide applicator certifications remain on a 3-year certification.
If a commercial applicator recertifies by attending a Commercial Continuing Instruction Course (C-CIC), this schedule remains unchanged. Applicators will still need to attend a C-CIC in 2020 if they plan to recertify by training. The ISU Extension and Outreach Spring C-CIC programs were completed as scheduled. Fall C-CIC programs will restart again in October. More information is available on the ISU Pesticide Safety Education Program website.
Private pesticide applicators with certifications that were current up to Dec. 31, 2019, will be able to purchase and apply restricted use pesticides for the 2020 growing season. Private pesticide applicators whose certification expired Dec. 31, 2019, and planned to recertify by testing now have until Dec. 31, 2020, to meet that requirement.
Private pesticide applicators who plan to recertify by attending Private applicator Continuing Instruction Course (P-CIC) programs and were unable to participate in a 2019-2020 P-CIC will now have until Sept. 30, 2020, to attend the 2019-2020 CIC program.
More information regarding 2019-2020 P-CIC programs will be communicated as it becomes available. The 2020-2021 P-CIC program will continue as scheduled and run from Dec. 1, 2020, to Apr. 15, 2021.
Iowa pesticide applicators do not need to wait until the end of the year to apply for recertification and are encouraged to submit a request once they have completed testing or training requirements.
This waiver does not apply to individuals who are not certified. To become certified, a potential pesticide applicator will still need to pass the appropriate exam(s). ISU Extension and Outreach will work with IDALS to help provide testing sites once testing activities resume.
Pesticide company/business license requirements remain unchanged.Category: Pesticide EducationTags: pesticideapplicatorrecertificationcertified applicators
Over the past several years as row crop prices declined, farmers and landowners across the nation have searched for alternative crops that might improve the financial bottom line. With the passage of the 2014 and 2018 farm bills, industrial hemp became one of those possible alternative crops. The 2014 farm bill established industrial hemp (hemp with a tetrahydrocannabinol [THC] concentration of 0.3% or less) as a potential crop, separating it from its illegal relative, marijuana. The 2018 farm bill removed hemp from the list of controlled substances and established hemp as an agricultural commodity, including the provision of crop insurance for hemp. While the farm bills cleared federal hurdles for hemp, it is still up to each state to pass laws legalizing the crop and to submit a plan to the USDA outlining the state regulations and laws guiding hemp production, testing, licensing, and transport. Iowa has passed a law to legalize hemp and our state plan was accepted by the USDA on March 20, 2020.
Hemp is a versatile crop that can be grown for seed, fiber, or oil. Hemp seed has potential as a food or feed product, but the food or feed products must be approved by the Food and Drug Administration (FDA) for food products and the Association of American Feed Control Officials (AAFCO) for feed products. Currently, hemp seed and hemp seed oil can be utilized in food products. There are currently no approved uses for any form of hemp as a feed ingredient. Hemp seeds can be crushed, like soybeans, to produce oil. Hemp seed oil has industrial and cosmetic applications, such as soaps and shampoos. Hemp fiber can be used in paper, textiles, fabrics, and various construction materials. As the fiber is flexible, yet durable, it has potential as a substitute for fiberglass. While the seed and fiber have several potential markets, another aspect of hemp that has attracted a lot of interest is hemp for Cannabidiol (CBD) oil. CBD is a non-psychoactive compound that can be extracted from hemp in oil form. It should be noted that CBD oil is different than hemp seed oil. CBD oil can be extracted from various parts of the hemp plant, but the most concentrated form is captured from unpollinated hemp flowers. Rough estimates suggest it takes 20 pounds of hemp flower to produce a pound of CBD oil. CBD oil is reported to have medical applications like relieving pain and reducing symptoms for a variety of ailments. However, there is scant research to back up those claims and any medical applications (beyond use in topical or cosmetic applications, such as lotions or skin creams) require FDA approval.
The production process for hemp depends on the targeted market for the hemp. For the fiber market, producers would choose hemp varieties that can be planted densely, forcing the plants to maximize resource allocation to the stem. For the seed market, planting density would be reduced to maximize seed growth. For CBD production, plant density is reduced even further, to allow the hemp plants to bush out and maximize flower production. Given the desire for hemp flowers for CBD extraction, the male plants are removed to avoid pollination. CBD production in outdoor facilities can be challenging due to the potential for cross-pollination from wild hemp that grows in ditches and other disturbed habitats in the state.
The marketing opportunities for hemp have revealed themselves in a variety of ways. A few clothing lines, such as Patagonia, have introduced hemp clothing items. Several companies have explored using hemp fiber as insulation or as a natural strengthening agent in construction and building materials (example: hemp-crete, concrete with hemp fibers mixed in). But many folks have concentrated on the potential for food, feed, and health products, especially from CBD and other chemical compounds. You’ve likely seen hemp products in grocery stores, convenience stores and assorted other shops over the past couple of years, targeting the food and health markets. The problems are that many of the applications were just test runs or, in some cases such as with CBD products, illegal markets. As was mentioned earlier, while hemp seed oil is legal for food products, CBD oil is not.The availability of CBD products on store shelves has definitely led to confusion in the marketplace and created the illusion that all potential products that can be created from hemp are legal.
To me, the biggest challenge for anyone exploring hemp, either as a producer or as a landowner with a tenant possibly producing hemp, will be to secure a marketing channel. For the majority of Iowa’s agricultural production there are numerous markets where producers can sell their crops, animals, and associated products. For hemp, that is not the case. Currently, there are no organized hemp markets, nor hemp processors, in Iowa. This is not the type of market where you should take a Field of Dreams approach (“If you grow it, processors will come”) as production costs can be extremely high and the approval process for hemp, and especially CBD, products could take considerable time. The market conditions for hemp in many of the states that moved before Iowa show that the development of hemp markets takes time. See, for example, these stories in Forbes, Harvest Public Media, and the Hemp Industry Daily. Before you or your tenant put a hemp seed or clone in the ground, you better know where your markets are, or better yet, have a contract with a processor already in place. You (and your tenant, in the case of a landowner) also need to understand the potential legal and marketing challenges if your hemp crop is tested and found to exceed the 0.3% level for THC. Who pays for the destruction of the crop? (Answer – you do. If the tenant does not pay for destruction, then the landowner would have to pay.) What are the legal ramifications if your crop exceeds the THC limit? (Answer – if you exceed the allowable ‘negligent violation’ level, criminal charges could be filed.) Given the ever-changing legal and regulatory scene for hemp, it would make a great deal of sense to review any hemp business prospects with an attorney.
At the publication of this article, neither CBD extraction nor processing is legal in Iowa. There is a bill in the legislature that would make it legal, but with the legislative shutdown due to COVID-19, we do not know when the legislature will reconvene again. And, if the bill does pass and is signed into law, regulatory requirements will be put in place, making the processing site equivalent to a licensed food processing facility. If you grow hemp for CBD it is likely that the 2020 crop will need to be transported out of Iowa for extraction. Hemp prices are like hemp processors, hard to find currently. But the general trend reported in the hemp industry is for lower prices. Hemp Benchmarks has created a hemp price index, based on prices they have found in three of the largest hemp producing states (Colorado, Kentucky, and Oregon). That index has fallen by 84% from July 2019 to January 2020. At least three Kentucky processors (Atalo, GenCanna, and Sunstrand) filed for bankruptcy in 2020. It is difficult to create new markets, especially when the product faces significant legal and logistical challenges. While in the long run I believe that hemp will develop as a fruitful crop for some producers in Iowa, the short-term prospects are dim for most who will pursue hemp this year. The few who will be successful will need to do a lot of homework and preparation to produce and market their crop. That homework includes knowing who you will sell to and how well they are set up financially. As the bankruptcies in Kentucky highlight, just because they’re processing today, it doesn’t mean they’ll be processing tomorrow.
The agricultural economy has been rough the past few years. Traditional crop returns have not been strong and farm incomes/balance sheets have been in decline. Producers and landowners are searching for alternative crops that offer any prospects for profitability. We’ve seen these types of agricultural “rushes” before: emus, ostriches, Jerusalem artichokes, Aronia berries, etc. It’s not that these products did not have a market. It’s that these markets were overhyped and initial production over-exceeded (in some cases, greatly) what the market could bare. Hemp is setting up to have a similar path. A few folks will be successful with the crop, but many will likely see hemp as a flame-out, a lot of cost sunk into a crop with no real opportunity for returns.Category: Crop ProductionTags: hempeconomicsgrowing hemphemp industryhemp seedalternative crop
As temperatures warm this spring, cover crop termination is on the to-do list for some Iowa fields. Killing cover crops with herbicides is the most common termination method. The effectiveness of herbicides at terminating a cover crop depends primarily on three things:
- Cover crop species and growth stage
- Herbicide and rate used
The cool and fluctuating temperatures encountered in spring often make terminating cover crops challenging. Farmers are limited to a few products like paraquat (Gramoxone; group 22), glufosinate (Liberty; group 10), or glyphosate (Roundup; group 9) for cover crop termination. Glyphosate is the most consistent option for termination, especially as cover crops increase in size. The group 1 herbicides (e.g. clethodim, fluazifop, etc.) do not provide effective control of cereal rye. If cereal rye or other grass species are seeded with a legume, inclusion of 2,4-D or dicamba with glyphosate will improve consistency of control. This addition can also be helpful if broadleaf winter annuals are present.
In a study encompassing eight site-years across five states, treatments containing glyphosate provided the most consistent cereal rye control (Figure 1). Cereal rye ranged from 5-54 inches tall at termination in the experiments. While control of cereal rye did not differ statistically between most paraquat and glyphosate treatments, paraquat-based treatments were much less consistent than glyphosate-based treatments. Glufosinate treatments were less effective and less consistent than glyphosate treatments. While paraquat can provide acceptable control in some situations, neither glyphosate alternative (paraquat, glufosinate) provides as consistent control as glyphosate under the cool and variable spring conditions. Dicamba combinations with the three burndown herbicides provided similar results to 2,4-D combinations (data not presented).
Figure 1. Control of cereal rye cover crops with select herbicide treatments.
* represents treatment mean; box represents the mid 50% of the data set, providing information on consistency of treatments. Herbicide rates: glyphosate: 1.0 lb/A; paraquat: 0.75 lb/A; glufosinate: 0.5 lb/A; 2,4-D: 0.5 lb/A; saflufenacil: 0.36 oz/A; metribuzin: 0.12 lb/A. Herbicides applied in 15 gal/A. Adapted from Whalen et al. 2020.
Figure 2. Cereal rye cover crop at the ISU McNay Farm planted early September 2017. Photo taken March 30, 2018.
Vegetative growth in rye requires temperatures of at least 38 F. While air temperatures may be favorable some days, cool soil temperatures can slow growth. Herbicides are most effective on actively growing plants; thus, very early spring termination treatments may provide less than complete control. Leaving a small check strip is a simple and easy way to see if the cover crop is dying following termination.
Iowa State University researchers generally recommend terminating the cover crop with herbicide 10 -14 days prior to planting corn to protect yield; however, that time frame is less critical for soybeans. Waiting to terminate until after your crop is planted, especially in non-GMO corn, can be risky. Termination options are more limited, and the cover crop can quickly become an uncontrollable weed in non-GMO crops. Additionally, it is important to check with your crop insurance agent for any specific cover crop requirements that they may have prior to planting corn or soybeans.
Whalen DM, Bish MD, Young BG, Conley SP, Reynolds DB, Norsworthy JK, Bradley KW (2020) Herbicide programs for the termination of grass and broadleaf cover crop species. Weed Technol. 34: 1–10.Additional information on cover crop termination:
- ICM Article: Research Shows Extra Cover Crop Growth Prior to Soybeans Provides Benefits
- ICM Article: Cereal Rye Cover Crops, Allelopathy and Corn
- Cover Crop Termination, IPM University of Illinois
- Cover Crop Termination, University of Wisconsin Extension
- Successful Cover Crop Termination with Herbicides, Purdue Extension
Claims of poor fertilizer application and visual striping in fields have increased in recent years. This issue impacts all sectors of the supply chain including growers, custom applicators, cooperatives and agribusiness insurance companies. An increase in documented application problems is primarily driven by a broader use of aerial imagery that can easily detect problems and an increase in use of dry nitrogen fertilizers. Cases of poor-quality application are seen less frequently with phosphorus or potassium products than with nitrogen because corn is not as sensitive to varying rates of these nutrients. Prior to applying dry fertilizer, follow these guidelines to achieve the best possible quality during application.
Calibrating the spreader
Figure 1. Yellow streaks are visible across this field photographed in mid-August. To correct this, the machine operator should have set the guidance working width about 10’ narrower to overlap more in these areas.
Whether using a spinner spreader or an air boom-type spreader, the machine should be properly calibrated. Machines should be calibrated every year for each product and should be re-calibrated if product conditions change throughout the season. It’s important to calibrate the product metering system as well as checking the distribution across the spread width of the machine. Complete spread pattern test kits are available to support this. This online article (FABE-561) from The Ohio State University explains this calibration process.
Calibrating the product metering system involves collecting and weighing product as it comes off the conveyor. This ensures the control systems spins the conveyer at the proper speed based on the machine ground speed, gate opening, and product density.
Checking spread distribution involves setting catch pans on the ground and driving the machine over them while applying (Figure 2). Each pan is dumped into an individual vial and measured to examine the spread distribution across the width of the machine (Figure 3).
Figure 2. Typical distribution of fertilizer calibration pans that are spread across the width of the spreader to catch calibration samples. The fertilizer spreader is operated at typical field application speed and rates to determine the distribution of material across the width of a spinner spreader. (Image courtesy of The Ohio State University FABE-561)
Figure 3. The small amount of product on each end of the pattern is expected since this is from a dual spinner machine, which relies on some pass-to-pass overlap to ensure a full rate is applied at the edges of the spread width. Notice the vial in the center appears to have more product than the surrounding vials. Overapplying in the center of the machine is a common issue with poorly adjusted spinner and air boom type machines. Information on correcting spread pattern problems can be found in this article (FABE-562) from The Ohio State University.
Spinner spreader distribution patterns often shift based on product density and application rate. It is typical to see distribution patterns that create a “W” pattern behind the spreader when application rates increase (Figure 4). Maintaining a consistent pattern across the width of the machine under all application rates is critical to eliminate local nutrient deficiencies. This is particularly important when applying nitrogen fertilizer due to increased crop responsiveness to reduced application rates.
Figure 4. Example application pattern from a spinner spreader under three different application rates when spreading dry Urea. The application pattern shifts towards a W pattern as the application rate increases.
Many spreaders can do a high-quality job of applying fertilizer; however, the fertilizer applicator is responsible for making the appropriate adjustments to optimize the machine for a specific product and rate.
Understanding the machine’s application distribution allows the applicator to adjust the machine as environmental conditions change. For instance, as wind speed and direction changes, it is crucial to evaluate how this affects distribution and to make needed adjustments. This may include changing the driving direction or adjusting spinner speed to narrow the application width to mitigate any negative impacts.Monitor product quality
One of the biggest causes of change in spreader distribution throughout the year is variability in product quality. It’s important to monitor density and hardness of the fertilizer granules as these can change due to storage conditions and environmental effects. Changes to density or hardness can have a direct impact on how fast the spinners can rotate without damaging the fertilizer granules, which affects how far the product can be spread.
To better visualize the effect product density has on spread distance and distribution, picture a golf ball and a ping pong ball. Both are similar in overall size, but the golf ball is heavier than the ping pong ball. The golf ball will travel farther because of the weight difference when thrown.
Product size is measured using a size grade number (SGN) scale (Figure 5) and hardness with a crush strength tester. Both tools are available through an equipment dealer or supporting vendor. These tools should be used to evaluate the product calibrated and to determine if the product quality changes during the season. If the product quality does change, the spreader should be recalibrated.
Category: Equipment and MachineryTags: fertilizer applicationdry fertilizerspreader calibrationfertilizer distributionspinner spreaderapplication pattern
Figure 5. High quality product (left) will be very uniform allowing for best spread distribution. Low quality product (right) will often have many broken particles, which will not travel as far and generally result in a higher rate near the center of the machine.
Significant sulfur (S) deficiency in Iowa crops was first documented about 15 years ago. First identified in alfalfa and then corn and soybean. Since then about 150 trials with corn (along with trials with alfalfa and soybean) have been conducted across the state, with approximately 50% of trials having a statistically significant yield increase. A main reason for the yield response to S in recent years, as compared to many years prior, has been reduction in atmospheric deposition as a result of the Clean Air Act. Other factors for increased S responses include fields with no manure applications, increased crop yields, refinement of phosphate fertilizers, and decreases in soil organic matter levels.Suggested sulfur fertilization
Research has indicated corn yield response to approximately 15 lb S/acre in fine textured soils and 25 lb S/acre in coarse (sandy) textured soils. These are suggested S rates for corn (and soybean). If in a corn-soybean rotation, apply these rates before corn as corn has been more responsive than soybean, and then no application needed before soybean. If in a corn-corn rotation, apply every-other-year. For alfalfa, apply 20-30 lb S/acre, with application not needed every year.
Accurately determining S deficiencies has been difficult. No S soil test has been calibrated (reliable) for Iowa crops (similar across the U.S. Midwest). In Iowa, there is no calibrated plant S test for corn or soybean. For alfalfa, sample the top six inches of the plant at early bloom. If the S concentration is less than 0.22-0.25% S, then S application is suggested. Strip trials, conducted with and without S across multiple years, is a good method to confirm fertilization need.Plant deficiency symptoms
Sulfur deficiency symptoms are easily confused with nitrogen deficiency. In corn, at early growth stages S deficiency shows as yellowing of the younger upper leaves with the older leaves remaining green. Because S is not easily translocated in plants, deficiency appears in the newer leaves. Interveinal chlorosis of the younger leavers may occur, however, interveinal chlorosis is not always an indication of S deficiency. With severe deficiency, the entire plant can show yellowing. In soybean, the plant may have an overall yellow appearance. In alfalfa, deficiency shows as a general yellowing of foliage, plant stunting, and spindly stems. In all crops, yield loss can occur without plant deficiency symptoms being present.Products
Since the plant available S form is sulfate (SO4-2), for an immediate crop response need apply a fertilizer containing sulfate. This would be the case for spring or early sidedress application in corn or soybean, and before any cutting in alfalfa. Because elemental S must be microbially oxidized to sulfate, it should be applied well in advance of crop need. For example, early fall before corn or soybean, or at the time of alfalfa establishment for multiple years.
Many S fertilizer products are available, including all animal manures and several byproducts. The first three fertilizers in the list are the most commonly used sulfate materials. Elemental S is also commonly used. There is sulfate in the common phosphate fertilizers. The S content is not guaranteed, with a range of 1.3-3.3% S (based on recent analysis of 118 samples by the Office of the Indiana State Chemist). Enough S that a significant amount can be applied with phosphorus fertilization, especially for multi-year applications.
- Ammonium Sulfate (21-0-0-24S)
- Ammonium Thiosulfate (12-0-0-26S)
- Calcium Sulfate (Gypsum) (0-0-0-17S)
- N-P-S products (ex. 13-33-0-15S)
- Polysulfate (0-0-14-19S)
- Magnesium Sulfate (0-0-0-14S)
- Potassium Magnesium Sulfate (0-0-22-23S)
- Potassium Sulfate (0-0-50-18S)
- Elemental S (0-0-0-90S)
- Sulfur in MAP, DAP, TSP
- By-Products (analysis varies)
- Lysine manufacturing
- Soybean soapstock processing
- Wallboard (gypsum)
- Flue-gas desulfurization
When S is applied in the sulfate form, application can be anytime in the spring through early crop stages. For elemental S, it should be applied well in advance of crop need, or in combination with a sulfate containing fertilizer. Sulfur can be applied broadcast, banded, and in combination with nitrogen, phosphate, and potash fertilizers, or mixed with liquid fertilizer (check compatibility). Ammonium thiosulfate should not be placed in the seed furrow as significant seedling damage can occur.Summary
- Sulfur deficiency has been common in Iowa.
- Many products are available to correct deficiencies.
- Sulfate containing products should be used when application is close to crop demand.
- Manure is a good source of S.
For additional information, see ISU Extension and Outreach publications
CROP 3072, Sulfur Management for Iowa Crop Production.
IPM 42, Nutrient Deficiencies and Application Injuries in Field Crops
After another relatively wet fall, late harvest season, and mild winter, early weed management may be important this spring for those who have persistent issues with winter annuals such as field pennycress and horseweed/marestail in no-till. Winter annuals resume growth soon after the arrival of warm temperatures, so as soon as fields are fit, the weeds will be susceptible to spray.
A common winter annual, horseweed/marestail, prior to bolting in the spring.
Applications made prior to planting increase the consistency of control of these weeds, particularly horseweed. Many of these weeds are either flowering or beginning to bolt, where the stems elongate, at the time of planting. Achieving full control of weeds at these stages becomes difficult.
Effective burndown treatments should follow herbicide label suggestions for carrier type, carrier volume, nozzle type, and environmental considerations. Treatments made on sunny days with warm daytime and nighttime (>40F) temperatures will generally be more successful than those in cooler conditions.
When selecting burndown treatments, consider the likelihood of resistant horseweed biotypes in the field. Herbicide group (HG)1 9 (glyphosate) and HG 2 (ALS) resistant populations are widespread across the state. Including 0.5 lb a.e. 2,4-D LVE, 0.25-0.5 lb a.e. dicamba (HG 4) or 1 oz Sharpen (HG 14) or another saflufenacil product to glyphosate will increase the consistency of horseweed control, even in fields without glyphosate resistance.
Check pesticide labels for planting restrictions; most 2,4-D labels have a 7-14 day planting restriction for corn or soybean following a 2,4-D application. Ester formulations of 2,4-D allow for a shorter interval to crop planting than amine formulations. In addition, esters often perform better under the cool conditions commonly encountered with spring applications. In dicamba resistant soybean, there is no planting restriction when using dicamba preplant, but only dicamba products registered for these varieties can be used. In non-dicamba resistant soybean, a 14-day planting interval is required at 0.25 lb a.e. and 28-day for 0.5 lb a.e. Any dicamba product describing this used can be used on non-dicamba resistant soybean.
The use of an effective early burndown against winter annual and early spring weeds is an important first step to achieving a clean field for crop planting. By including a product with residual activity, fields should remain weed-free and will allow for a delay in the next herbicide application until after crop planting. While this application is not necessary in many fields, those no-till fields with known winter annual weed issues may be good targets for an early burndown this spring.
1The Group number refers to the site of action of a herbicide. The Group number is displayed on the first page of the herbicide label, and is important information for developing resilient weed management programs less likely to select resistant weeds.Category: WeedsTags: winter annualsannual weedsweed managementspringhorseweedburndown treatmentherbicide resistant weeds
With recent weather patterns, specifically high rainfall leading to wet soil conditions, some farmers have experienced damaging populations of slugs in their no-till fields. No-till fields are particularly affected since increased residue provides a stable, cool, and wet environment for these animals that are prone to desiccation (drying out). Oftentimes, farmers wonder if insecticides or seed treatments are effective at managing these non-insect pests. We will discuss management options for slugs in this article.
Slugs (Gastropoda) are members of the phylum Mollusca, which also contains clams, scallops, snails, squids, and octopi, among others. Molluscs have soft bodies with two regions: a head and a foot. These animals often have a hard exoskeleton, such as a shell or plate. However, slugs do not have a shell. They are essentially snails without a shell. Slugs have four front tentacles: two for the eyes and two that act as antennae. They are covered in slimy mucus and secrete additional mucus to aid in locomotion. Oftentimes, the slime trail is an indicator of slugs in the field.
A gray garden slug. Photo from Ohio State University Extension.
If you scout for slugs, you will likely find all life stages throughout the growing season. This is because slugs are hermaphrodites, and their mating habits are complex and not well synchronized. Their eggs, which are small gelatinous spheres, can be found under residue or in the soil. In general, slugs are most active and damaging April to June and September to October. They are most common in heavy, wet soils that are not tilled often and prefer slightly alkaline to neutral soils.
Slugs are nocturnal herbivores, so they generally feed from dusk to dawn, but they may feed during the day if it is raining. Activity increases with temperatures below 70°F and with higher humidity (they prefer 100% humidity). Slugs can feed when temperatures are as low as 34°F, although their activity is decreased. Activity is also reduced at temperatures greater than 80°F, because slugs are 80% water and are prone to desiccation; therefore, warm, dry conditions slow slug activity while mild, wet conditions promote activity. Significant slug populations are most likely during a wet spring that follows a mild winter, or any spring following a wet fall, because wet soils promote egg-laying.Plant injury
Slugs are considered serious pests of wheat, barley, oats, rye, corn, soybeans, tobacco, canola, alfalfa, and other cereals or legume forage species when grown under no-till or reduced tillage. They can feed directly on the seeds or seedlings, leading to plant death and poor stands. Additionally, slugs can damage seeds, roots, stems, leaves, and flowers by scraping the surface with their radula. Feeding tends to be greater on leaves closer to the soil, and young plants are preferred. Slugs may also eat fungi, plant residue, soil organic matter, small invertebrates, and occasionally each other.
Corn and small grains often exhibit window-pane damage and then shredding, as slugs scrape strips in the leaves. In soybean, slugs can create craters in the cotyledons or leave ragged holes in the leaves. In addition, slugs can destroy the apical meristem (growing point), leading to plant death, or they can completely defoliate plants under high populations. Seeds and seedlings are at greater risk of damage if the furrow or slot is left open during planting as this creates a dark, cool “tunnel” for slugs to effortlessly travel from seed to seed.
Left: Slugs create “windowpane” injury on corn. Photo by Marlin Rice. Right: Slugs create “craters” in soybean cotyledons. Photo by Nick Sloff.
To estimate the absolute density of slugs in the field, a soil sampling method exists; however, it is labor intensive and impractical for most farmers and crop consultants. Less intensive methods include looking for adults in the fall, looking for eggs and overwintering individuals before seeding in the spring, inspecting emerged crops with a flashlight at night, or placing artificial shelters (shingles, boards) in the field and checking underneath them occasionally. Fields with a history of slug issues, fields with a lot of surface residue, low-lying fields, fields with manure applications, and fields with heavy soils should be prioritized when scouting.
Because they’re soft-bodied with no shell, slugs have many predators, such as frogs, toads, snakes, birds, ground beetles, rove beetles, firefly larvae, marsh flies, harvestmen, wolf spiders, centipedes, and parasitic nematodes. Any insecticide used for management would have an impact on the effectiveness of natural enemies.Management
Reduce soil residue:
- Shallow disking can reduce populations.
- Using row cleaners to remove residue over the row may help reduce damage when slug populations are low.
Avoid slugs early in the season:
- Planting earlier may limit damage if plants have enough growth before eggs hatch.
- Ensuring seed slots are closed at planting may help minimize damage.
- Having other plant species present in the field may reduce slug damage to the crop: weeds, companion plants, or recently terminated cover crops have been preferentially fed upon in field studies. However, extra residue provided by cover crops may increase slug issues as well.
Promote crop vigor:
- Planting later, when soils are drier and warmer, can promote quick crop growth even though slugs would be active.
- Choosing crop varieties that have higher emergence and vigor ratings can help promote early growth.
- Pop-up fertilizers at planting could encourage quick growth to “outrun” slug damage.
Foliar insecticides have inconsistent results, but baits may be used to manage slugs:
- Insecticides, particularly chlorinated hydrocarbons and organophosphates, do not appear toxic to slugs, are inconsistent, or require very large doses.
- Neonicotinoid seed treatments are not lethal and may actually increase feeding.
- Carbamates can have activity as baits, but not foliar sprays.
- Metaldehyde baits are effective molluscicides; however, in the U.S. they are only labelled for use on ornamental plants, some small fruits and berries, citrus, some vegetables, and grass grown for seed. They are NOT registered for ANY USE in Iowa.
- Other baits are available that include iron phosphate, iron chelate, or sulfur, which must be ingested to be effective and may not be cost-effective for farmers.
- Any bait should be applied when juveniles or adults are present in the field, as their efficacy is easily diminished by rainfall.
Poisoning slugs with nitrogen or repelling them with salts may minimize damage, but these approaches have not been tested in field studies:
- Applying a nitrogen-based spray at night may poison slugs, however, they may also burn the crop.
- Applying dry ammonium sulfate or salt-based herbicides over crop rows may repel slugs.
- Consider the costs and benefits of these approaches. It is possible these tactics are not economically justifiable if severe damage has not occurred.
- Additionally, slugs seek shelter under windy conditions and are nocturnal feeders, so any application should be made under calm, mild conditions at night.
No economic thresholds exist for slugs in crops, but typically crops have most of the growing season to recover from damage that was not lethal. Corn can typically withstand at least 40% defoliation during early stages without yield reduction. Soybean only suffers minor yield loss if the unifoliate leaves sustain 50% defoliation, but no yield loss occurs when trifoliates sustain the same amount of defoliation. However, stand reductions are more concerning, and farmers should decide if treatments or replanting are necessary given the conditions.Management summary
Reducing soil residue
With low slug populations
If adequate growth achieved prior to egg hatch
If soils are dry and warm
Closing seed slots
Other plant species
Weeds, companion plants, or cover crops
Choose those with high emergence and vigor ratings
Inconsistent results or large doses required
May increase feeding
Apply when juveniles or adults are present
Diminished with rainfall
May burn crops
Dry ammonium sulfate
May burn crops
May burn crops
Category: Insects and MitesTags: slugsslug managementinsecticides
Drone activity in agriculture continues to increase, and the aerial imagery generated can provide unique insight throughout the crop production season. Over the past decade the Federal Aviation Administration (FAA) has continued to evolve the requirements for the operation of small unmanned aerial systems (sUAS, UAS, UAV or drones) to create a reasonable legal pathway for use in agriculture.
In agriculture, if drones are used to collect imagery to help make management decisions, this is classified as commercial use of the drone. This includes collecting imagery for scouting crops, reporting crop damage or determining tile locations. The FAA has specific rules that must be followed, which are outlined under the FAA’s Part 107 regulations. This involves obtaining a remote pilot certificate, registering the drone with the FAA and displaying the assigned registration number (N-number) on the aircraft, and abiding by the FAA’s rules for operating a drone. To meet these requirements, the FAA suggests the following steps.Step 1: Learn the Rules
Below are a few key rules from the FAA website pilots should understand to safely and legally operate a UAS for agricultural use under Part 107: Summary of Small Unmanned Aircraft Rule (Part 107).
- Unmanned aircraft must weigh less than 55 pounds.
- Unmanned aircraft must remain within the visual line of sight of the remote pilot or visual observer in command and the person manipulating the flight controls.
- Operate only during daylight or civil twilight (30 minutes before sunrise to 30 minutes after sunset) with appropriate anti-collision lighting.
- Yield right of way to other aircraft.
- Maintain maximum altitude of 400 feet above ground level (AGL).
- No carrying hazardous materials.
- Operations in Class G airspace are allowed under Part 107 without Air Traffic Control (ATC) permission. Operations in Class B, C, D and E airspaces (typically found around most airports) require ATC permission to fly. There are options to obtain permission to operate under the Part 107 in these areas by obtaining authorization through the Low Altitude Authorization and Notification Capability (LAANC) system.
There are many resources and online apps that can be used to understand what airspace your UAS operations are located in. The FAA website Visualize it allows a person to look up a field’s location to understand the different airspaces and altitude requirements surrounding the location. B4UFLY is an app offered by the FAA used to understand specific airspaces and other temporary flight restrictions (TFR) that might be in the area. These or similar resources should be checked before any flight. Many Iowa fields are located in close proximity to a rural airport. There are airspace restrictions to consider in these areas, and the FAA has established reasonable procedures for conducting safe and legal operations in these areas. These procedures are outlined in many of the online training resources listed in this article.Step 2: Become a FAA-Certified Drone Pilot
To become an FAA-Certified pilot, you need to pass an electronic knowledge test. The FAA’s PSI exam center can be used to schedule the exam and locate a testing center. Before scheduling your exam, make sure to View Test Authorization Requirements. As of January 2020, an FAA tracking number (FTN) is required before you can schedule the exam. This can be obtained by creating an account with Integrated Airman Certification and Rating Applications (IACRA). The FTN links your FAA profile to your exam results and, eventually, your remote pilot certificate.
There are companies that provide study materials to help prepare for this exam. The FAA also has materials that should be reviewed before taking the exam: Airmen Certification standards, Knowledge Test instructions, Knowledge Test Study Guide, Knowledge Test Sample Questions and Pilot’s Handbook of Aeronautical Knowledge. There are also instructional classes offered by organizations periodically. While these may be more expensive than other studying options, many of these classes are taught by pilots who can provide real-world examples of the application of their knowledge. One such class is offered by Kansas State University’s Unmanned Aircraft Systems Group. There are also several mobile apps available for test preparation. The Prepware Remote Pilot by ASA app has proven to be a valuable study tool for many and is available for a small fee in your app store.Step 3: Register your drone with the FAA
All drones weighing over 0.55 pounds must be registered with the FAA and receive an N-number, which needs to be visible on the exterior of the drone. Print a copy of the registration card and keep it available to the pilot operating the drone. The registration is $5 per drone and is valid for three years. To register your drone, use the FAA’s DroneZone website.Timeline
The entire process, from studying to receiving the official certificate in the mail, can take over two months. Generally, studying and preparing for the exam will require at least a week. Testing slots are often booked several days out, so book the exam date prior to or while studying the material. After passing the exam, make sure to link the exam to your application within your IACRA account. If you don’t pass the exam, you must wait two weeks before retaking it.
A recurrent knowledge test must be passed within 24 calendar months after passing the initial exam and every 24 calendar months thereafter. A new certificate will not be issued for passing the recurrent knowledge test. Instead, the pilot must show a copy of their recurrent knowledge test report upon request.Category: Equipment and MachineryTags: dronesdrone usageUAVsoperating dronesdrone rules
Many states, including Iowa, received a record amount of precipitation in 2019. In fact, the past two growing seasons have been especially wet. Consequently, this has created a number of issues for farmers, including reports of millipedes damaging crops under no-till production in Iowa, which is likely due to a combination of wet conditions and high residue. People that experience millipedes under these conditions frequently ask if insecticides or seed treatments will provide control of these pests. Although millipedes are not insects, they commonly fall under the realm of entomology, alongside many other animals (spiders, centipedes, mites, etc.). We will provide a brief discussion of non-insect crop pests, particularly millipedes and isopods, and potential management options.Why are no-till fields primarily affected?
One thing that is common among millipedes and isopods is that they need moist, cool environments to prevent desiccation (drying out). No-till production provides this stable environment by leaving residue on the surface and protecting the ground from sunlight, which heats and dries the soil.
Wireworms and grubs are examples of insect pests that are known to cause damage to no-till crops early in the season. Cooler soil temperatures slow germination and seedling growth, leaving seeds and seedlings more vulnerable to injury from pests for an extended period of time.Millipedes (Diplopoda)
Like insects, millipedes are arthropods, meaning they have an exoskeleton, segmented body, and paired jointed appendages. However, millipedes differ in that they have two pairs of legs per body segment. Contrary to popular belief, millipedes do not have 1,000 legs; they typically bear 80-400 legs, though some species may have more. They are cylindrical in shape.
Millipedes feeding on soybean cotyledons. Photo by Brian Lang
Millipedes are saprophagous, which means they normally feed on decaying organic matter. They live in soil or litter, which also protects them from hot, dry conditions that promote desiccation. When millipedes are pests, they ingest the soft and easily digestible parts of plants, such as young seedlings or roots. Damage usually occurs at or below the residue surface. Often, millipedes will feed on decaying seeds or seedlings that have been compromised by another issue, such as environmental conditions, seedling diseases, or other pests.
Millipedes are prey for a number of organisms, including birds, mole rats (and other burrowing animals), crickets, ants, scorpions, assassin bugs, parasitic mites, and ground beetles. There are also nematodes that are endoparasites of millipedes and special fungi that can attack millipede legs to prevent mobility.
Unsurprisingly, little research has been done to evaluate how insecticides affect millipedes. Anecdotal evidence suggests that neonicotinoid seed treatments do not affect millipedes in field crops, but pyrethroids can kill millipedes if the chemical contacts their body. Remember that millipedes live in soil or litter, so contacting them with insecticides may be challenging.
Any practice that limits residue on the soil surface can help reduce damage by millipedes. If tillage is not an option, delay planting to avoid cool, wet conditions. Planting under more ideal conditions helps promote rapid growth, which may allow the crop to escape any damage by millipedes in the field.
- Check for other potential issues – millipedes may not be the primary cause.
- Limit residue on soil surface.
- Delay planting until soil is warmer and dryer.
- Use pyrethroids, but ONLY if the chemical will contact the millipede. This is challenging with soil residue. No economic threshold currently exists for millipedes in field crops since they are rare pests.
Isopods are also arthropods in the subphylum Crustacea, meaning they are closely related to crabs, lobsters, and shrimp. Their bodies are elongated, flat, and somewhat arched. Usually isopods have seven pairs of legs and possess swimming limbs. Most isopods are aquatic, but the ones we see are terrestrial. Woodlouse, slater, sowbug, pillbug, and roly-poly are all common names for isopods.
A pillbug. Photo from wiki.bugwood.org.
Like millipedes, isopods are soil dwelling and generally feed on dead plant tissue or soil organic matter. They are most active in the spring (when mating occurs) and at night. They are prone to desiccation, so they are less active under higher temperatures, lower humidity, and clear skies. However, increased temperatures in combination with high humidity may increase activity. In general, a moist habitat is required for survival, so isopods seek dark, damp areas such as soil, residue, or cracks in the field.
Typically, isopods are indicators of good soil health; however, they have been observed feeding on seeds, stems, flowers, and leaves of alfalfa, sunflower, cereal crops, and soybean. Isopods can sever the soybean hypocotyl below the apical meristem (growing point), leading to plant death. In Kansas, no-till soybean producers have had to replant soybean fields because of isopod feeding. Isopods tend to prefer decayed tissue of dicot plants because monocot residues are not as digestible and plant defenses generally inhibit feeding on living tissues.
Foliar-applied chlorpyrifos and beta-cyfluthrin may reduce isopod populations in soybean. However, crop residue can interfere with the efficacy of these products because it is difficult to contact the isopods living in and under residue. Isopods do not typically feed in the seed zone, so at-planting insecticides have not been effective. Seed treatments (imidacloprid and thiamethoxam) can be effective, but control is variable. Isopods must feed on enough germinating plants to acquire a lethal dose of insecticide and significant stand loss can occur in that time.
Any areas with high residue may be at risk for damage by isopods. Less soil moisture and shelter availability lead to lower population of isopods in conventionally tilled fields. Tillage every other year has been effective at reducing the amount of time for populations to reach damaging levels. Cleaning residue away from the rows prior to planting and controlled burning of crop residue has not been effective for isopods. Varying planting date by a few weeks (earlier or later) has been effective, but it might not be feasible, especially considering recent weather patterns. In areas with frequent stand loss from isopods, higher seeding rates may compensate for stand loss, but the grower must consider the increased cost of seed and the yield potential of the field. Additionally, consider if a higher seeding rate is better than a potential replant scenario.
- Use occasional tillage (e.g., every other year).
- Vary planting date by a few weeks (either early or late).
- Increase seeding rate but consider economics.
- Apply insecticides, including organophosphates and pyrethroids, but ONLY if the chemical will contact the isopod. This is challenging with soil residue and nocturnal pests. No economic threshold currently exists for isopods in field crops since they are a rare pest.
Iowa State University (ISU) recently completed a five-year study of high-speed planter equipment in corn and soybeans. The study utilized a 12-row planter equipped with the Precision Planting SpeedTube high speed planter system and a 24-row planter equipped with the John Deere ExactEmerge high speed planter system (Figure 1). Both planters utilized individual row hydraulic downforce and were tested using a side-by-side strip trial experimental design. Each planter was used on approximately 400 acres per year. Additionally, a third planter with a standard drop tube seed delivery system was included in select fields for seed spacing comparisons.
Figure 1. Seed delivery system for Precision Planting SpeedTube (left), John Deere ExactEmerge (right). Photos courtesy of Precision Planting and John Deere.
Crop yield, particularly in corn, may be influenced by seed singulation and spacing. The most significant yield losses occur when ‘skips’ occur at the planter meter, which result in no seed being planted. This creates a total yield loss for that potential plant. Overplanting with doubles or crowding plants through poor singulation will also cause reductions in yield. As a general rule of thumb, a standard deviation of two inches is acceptable for well-maintained traditional planters and will result in minimal yield impacts in corn. Both high speed planters tested showed consistent and distinctive corn spacing at all speeds tested (Figure 2). Traditional drop tube planters exhibited a noticeable trend in reduced spacing consistency when speeds increased from 5 to 10 miles per hour.
Downforce and closing wheels
Figure 2. Summary of corn spacing uniformity for conventional and high-speed planting systems. High speed planter systems maintain high quality placement uniformity independent of planting speed and eliminate the risk of yield reductions from seed spacing in corn.
High speed planting will require increased row unit downforce and increased closing wheel force due to the increased planter travel speed. The exact settings for each system will be dependent on your field conditions and spring tillage practices. In general, expect 20-40 pounds of increased downforce margin and one additional notch in the closing wheel pressure when planting at speeds over 8 mph.
As expected, increasing planter speed resulted in a direct improvement in planter productivity. In the majority of field conditions, we found 8-9 miles per hour to provide a good balance of increased productivity with excellent seed singulation and placement and minimal challenges associated with row unit bounce or loss of ground contact.Considerations for Soybeans
Improved soybean singulation with high speed planters did result in improved survival rate of soybeans. On average, the ExactEmerge planter produced soybean survival rates of 84% as compared to survival rates of 77% for the SpeedTube planter (Figure 3). Experiments showed that the difference in survival rates correlated with the increase in planted doubles and triples with the SpeedTube design and the increased death rate of these crowded plants. All soybeans in this trial were treated with fungicide prior to planting. Improvements in soybean survival rates offer a direct opportunity to reduce seed input costs and achieve an equivalent at harvest population.
High speed planting of large soybeans did create some challenges with the Precision Planting seed delivery systems. The SpeedTube seed delivery tubes were susceptible to plugging when planting large soybeans (2,750 seeds/pound or less) at rates exceeding 100 seeds/sec. This corresponds to a maximum speed of approximately 7 miles per hour when planting 160,000 seeds/acre in 30 inch rows. No plugging issues were observed in the ExactEmerge planter when planting the same seed size due to the differences in the seed delivery system design.
Figure 3. Summary of soybean survival rate comparison between high speed planter technologies. High speed planters that provide true singulation of soybean will have a higher soybean survival rate due to reduced seed doubles and plant crowding.
Two high speed planting systems were evaluated as part of a five-year, field scale study on planting system performance. Both systems demonstrated excellent corn singulation and spacing at speeds up to 10 miles per hour and confirmed the manufacturer advertised performance expectations. High speed planting can significantly increase daily planting productivity which will allow more crop to be planted during tight planting windows.Category: Equipment and MachineryTags: high speed plantingplantingplanting equipmentseed spacing
Perhaps you did not get planned nitrogen (N) applications accomplished last fall. Or you are pondering what the spring 2020 weather conditions might be – another wet spring? Are you are considering use of different products; if so how should they be handled?Preplant applications Urea, urea-ammonium nitrate solution (UAN), and other products
Fertilizers such as urea and UAN solution can be broadcast and incorporated with normal tillage before planting. Incorporating or injecting rather than leaving the fertilizer on the soil surface can prevent volatile N loss from granulated urea or urea in UAN as it converts to ammonium, or reduce runoff if a rapid rainfall (or snowmelt) event occurs. If time is critical and UAN application is made with preemergence herbicides, then surface application is an option, although more risky due to potential volatile loss from the urea remaining on the soil surface (especially in no-till). A rainfall of at least ¼-½ inch within approximately two days after application will eliminate volatile loss concern. UAN is half ammonium nitrate and half urea, therefore volatile loss potential from UAN is half of that with urea. Banding UAN on the soil surface will also reduce volatile loss to about half that with broadcast application. Predicting the amount of volatile N loss is difficult, but loss increases with high surface crop residue (especially no-till), moist soils that are drying, warm soil temperatures, many days without rainfall, high soil pH, low soil cation exchange capacity, and higher N application rates. Although an added cost to decrease risk of volatile loss, a urease inhibitor can be added to slow urea conversion which provides time for rainfall to move urea into the soil. Preplant or preemerge applications can be part of a weed-and-feed or split-N system, with a full N rate or rate to supply part of the total N application needed and the remainder applied sidedress.
Another fertilizer option is polymer coated urea, designed to delay urea release until soils warm up. To avoid product runoff, incorporate into the soil. Surface broadcast options, especially adapted to no-till, include ammonium nitrate and ammonium sulfate. These granulated products are either not used extensively in Iowa, or not typically used for main N applications, so there may be limited availability. Nitrification inhibitors, designed to slow conversion of ammonium to nitrate, have not shown adequate yield response in Iowa research when spring applied to justify use with ammonia, urea, or ammonium containing fertilizers.
If disturbing soil is a concern in no-till from injecting N, then broadcast application is an advantage. However, it also has the disadvantage of potential volatile losses from urea, surface runoff, or immobilization of N with surface residue, and is not a highly recommended application.Anhydrous ammonia before planting
Anhydrous ammonia has specific considerations. It must be injected, and the ammonia band will initially have high pH and considerable free ammonia which can damage corn seedlings and roots. There is no exact “safe” waiting period before planting, and injury can happen even if planting is delayed for a considerable amount of time. The risk of ammonia injury depends on many factors, with several that are not controllable. Risk increases if application is made when soils are wet and then dry (allowing ammonia to move up the injection track after application), with higher application rates, when soils with high clay content are wet (sidewall smearing of the injection track and ammonia moving toward the soil surface during application), and when soils are very dry and coarse textured (ammonia movement resulting in a larger band). A few management practices can reduce the risk of ammonia damage. Wait to apply when soil conditions are good, have a deep injection depth (6-7 inches or more), and wait several days until planting. If the injection placement relative to future corn rows can’t be controlled, apply at an angle to reduce entire sections of corn rows from being damaged. If the injection track can be controlled with GPS guidance, then offset a few inches from the future corn rows – with this guided system no waiting period is needed. There is a similar free ammonia or salt issue with shallow banded urea or UAN solution. Anhydrous ammonia nitrifies more slowly than products like urea or UAN solution, so it is a preferable preplant fertilizer for soils with greater potential for losses in wet conditions.Split/sidedress applications
There is a wide time period for split/sidedress applications. Sidedress injection can begin immediately after planting if corn rows are visible or GPS guidance is used. Be careful so that soil moved during injection does not cover planted rows or small corn plants. It is easiest to inject in the middle between rows and there is no advantage in attempting to place the injected band close to the corn row. Corn roots will reach into the inter-row at an early growth stage. Injected N can also be applied between every other row, and this will provide equivalent response as when placed between every row. Compared to preplant application, split/sidedress has greatest chance of improved response on soils with high leaching potential (sandy soils) and poorly drained soils prone to excess wetness and ponding.
For many soils, when planting after soybean there can be adequate N in the root zone to meet the needs of small corn plants. In wet and cool springs, where soil nitrate levels and mineralization rates are low, to avoid early N stress there should be a preplant or planting time N application. This is especially important for corn following corn, where there is a greater likelihood of low soil nitrate and added N is needed for early growth. Preplant or starter N can help meet early plant needs, and is especially important if sidedressing is delayed significantly or planned mid- to late-vegetative growth stage application.
With sidedressing, a urease inhibitor with surface applied and non-incorporated urea and UAN could help reduce volatile loss, similar to that described above with preplant applications. A dry soil surface may be more common within the growing season, which will reduce volatile loss potential. The rate of N applied, and the amount of potential N loss, has to be large enough to offset the inhibitor cost. Rainfall will eliminate volatile loss and is needed to move surface applied N into the root zone.
Broadcasting granulated urea, ammonium sulfate, or ammonium nitrate across growing corn can cause leaf spotting or edge browning when fertilizer granules fall into the corn whorl. Damage will be greatest with ammonium nitrate, but that product is not readily available in Iowa, and damage from ammonium sulfate is greater than with urea. The chance of damage increases with larger corn and higher application rates. As long as the fertilizer distribution is good, not concentrated over plants, and the rate reasonable, the leaf damage should only be cosmetic.
Broadcast application of UAN solution across growing corn has the potential to cause significant leaf burn and reduced early growth. Depending upon severity of damage, reduced plant growth may be visible for several weeks after application. Research conducted in Minnesota indicated that when corn plants were at the V3 growth stage (three leaf collars visible), phytotoxic effects were worse at rates greater than 60 lb N per acre (rates applied were 0, 60, 90, and 120 lb N per acre), but damage was not permanent and did not adversely affect stand or yield. When plants were larger than the V3 stage, plant damage was worse and some yield depression occurred with the 120 lb N per acre rate. Many herbicides are applied using UAN as the carrier to minimize trips across fields. However, this strategy is only recommended prior to crop emergence. Almost all herbicides prohibit application in N solutions after corn has emerged. Check herbicide labels closely.
If N is to be sidedress applied, then rates can be adjusted from results of the late spring soil nitrate test (LSNT). Soil samples, 0-12 inch depth, are collected when corn is 6-12 inches tall with rate adjustment based on the measured nitrate-N concentration. See ISU Extension and Outreach publication CROP 3140, Use of the Late-Spring Soil Nitrate Test in Iowa Corn Production.Summary
- There are multiple opportunities to accomplish springtime corn N fertilization.
- If you decide to change N applications, make certain needed fertilizer products and sidedress or high-clearance equipment will be available; or if hiring applications, the dealer or custom applicator can accomplish the applications.
- Consider the N volatilization potential of different materials when applying without incorporation or injection into the soil.
- Successful communication between farmer and dealer is key.
A common question when incorporating cover crops into a production system is, will the cover crop interfere with the performance of residual herbicides included with the burndown treatment? This article will discuss the fate of residual herbicides applied to crop residue and living cover crops, and how this may influence herbicide effectiveness.Crop residue and residual herbicides
Considerable research has evaluated the fate of herbicide intercepted by crop residue present on the soil surface in conservation tillage systems. Agricultural Engineers at Iowa State (Baker and Shiers, 1989) determined 70-90% of preemergence herbicides was washed off corn residue with 2.7 inches of rain, with the majority coming off in the first 0.6 inch of rain. There were small differences in washoff of different herbicides. This research indicates that herbicide interception by dead plant material isn’t a major concern.Cover crops and residual herbicides
While herbicide interception by dead plant material isn’t a major concern, interception by living plants could be a concern. Weed scientists at the University of Missouri (Whalen et al. 2020) studied how cover crop termination timing affected the quantity of sulfentrazone reaching the soil. Several cover crop species were established in the fall, and a combination of 2,4-D and glyphosate was applied either 21 or 7 days before soybean planting to terminate the cover crops. Authority Maxx (sulfentrazone plus chlorimuron) was included in the burndown mixture to provide residual weed control. The concentration of sulfentrazone in the upper five inches of the soil profile was measured immediately after application and throughout the growing season to determine the impact of interception by cover crops on the availability of residual herbicides.
Averaged over cover crop species, there was approximately a 50% increase in biomass between the early and late termination dates. This increase in biomass between termination dates reduced the amount of sulfentrazone directly reaching the soil by more than 50% (Figure X). Sulfentrazone soil concentrations declined by about 5% in both termination dates during the first 28 days following application, suggesting sulfentrazone intercepted by the large cover crops (late termination date) was not released into the soil as the cover crop degraded. The reduced availability of sulfentrazone was reflected in waterhemp control, with a 20% reduction in control between the early and late termination dates.Managing residual herbicides with cover crops
So how do we best integrate residual herbicides with cover crops? If cover crops are terminated early (less than 12-18 inches in height), residual herbicides should be included with the burndown application since there isn’t enough cover crop biomass to significantly suppress weeds. While a portion of the residual herbicide will be intercepted by cover crops with early termination dates, small cover crop plants break down quickly and it is likely some of the intercepted herbicide will reach the soil.
As termination is delayed and more cover crop biomass accumulates, the answer isn’t quite as simple. In fields with dense, uniform cover crop biomass, omitting the residual herbicide from the termination application and including it with the postemergence application may be advantageous. In this scenario the cover crop biomass can provide effective early-season weed control, replacing the residual herbicide applied at planting. Unfortunately, many fields have uneven stands of cover crop where there are areas with insufficient cover crop biomass to control weeds. Due to the risks of escaped weeds and increased selection pressure for herbicide resistance associated with total postemergence programs, including a residual product in fields lacking uniform stands of cover crops will be necessary.
Baker, J.L. and L.E. Shiers. 1989. Effects of herbicide formulation and application method on washoff from corn residue. Trans. ASAE. 32:830-833.
Whalen, D. M., L.S. Shergill, L.P. Kinne, M.D. Bish and K.W. Bradley. 2020. Integration of residual herbicides with cover crop termination in soybean. Weed Technol. 34:11-18.Crop: Cover CropCategory: Crop ProductionWeedsTags: residual herbicidescover cropscrop residuesulfentrazinecover crop termination
Chlorpyrifos is an organophosphate insecticide (Group 1B; IRAC) used to kill insects and mites on crops, buildings, animals, and other settings. All indoor uses of chlorpyrifos were phased out in the 2000s. Chlorpyrifos products are restricted-use pesticides, meaning sale and use of this chemical is restricted to certified applicators.
Dow Chemical Company received registration from the EPA for chlorpyrifos in 1965 and patented the chemical in 1966. Lorsban® and Dursban® are two widely recognized trade names for chlorpyrifos from Corteva™ Agriscience (the agricultural division of the 2017 Dow-DuPont merger). Lorsban® is labelled for a number of pests on field crops, horticultural crops (orchards, vineyards, vegetables), and ornamental plants such as Christmas trees.
On February 6, 2020, Corteva™ announced the end of chlorpyrifos production by 2021. This includes Lorsban® and Cobalt®, which are commonly used in Iowa for control of field crop pests, especially where pyrethroid insecticides are less effective. Other chlorpyrifos products that are registered trademarks of Dow® but distributed by other companies include Eraser™, Govern®, Hatchet®, and Whirlwind®.
Corteva™’s decision to end production of Lorsban® was made based on declining sales of the product, citing statistics showing demand for chlorpyrifos is less than 20% of peak demand in the 1990s.The good news
Other companies produce chlorpyrifos: ADAMA Agricultural Solutions Ltd., Cheminova (acquired by FMC Corporation), Gharda Chemicals, Ltd., and Platte Chemical Company, Inc. (also Loveland Products, Inc.). Products of these companies are distributed by a number of retail companies. Generic products will remain available for farmers to use.
Other organophosphate insecticides will also remain available for use, and new active ingredients with new modes of action are available to help manage soybean aphid in Iowa: afidopyropen (Group 9D; Sefina™ Inscalis® from BASF) and sulfoxaflor (Group 4C; Transform® WG from Corteva™) were both approved for use in soybean in 2019.
As of now, the Iowa Department of Agriculture and Land Stewardship (IDALS) has not been formally contacted by Corteva™ or the EPA regarding the status of Corteva™ chlorpyrifos products. Once more information is available, we will provide updates regarding future sale, distribution, use, and disposal of products, if necessary.The future of chlorpyrifos
Chlorpyrifos, like many other pesticides, has been under scrutiny in recent years for children’s health concerns, specifically low birth weight, reduced IQ and attention disorders. The EPA has continued registration despite many attempts to ban or limit use of the product and will evaluate potential risks of chlorpyrifos until the review deadline of October 1, 2022 when a final decision will be made. The EPA’s registration review process ensures that pesticides will not cause “unreasonable adverse effects” when used according to the label and that there is “a reasonable certainty of no harm from dietary and residential exposure”.
Demand will continue to drop amid regulatory restrictions, including a complete ban in the European Union and California. As of February 6, 2020, it is illegal to sell chlorpyrifos in the state of California and use and possession of chlorpyrifos will be illegal in 2021. Hawaii and New York will ban the chemical by 2022, and Oregon, Washington, Connecticut, New Jersey, and Maryland all have plans to implement a ban in the future.What does this mean for farmers?
- Among other chlorpyrifos products, Lorsban® and Cobalt® will not be available from Corteva beyond 2020.
- Chlorpyrifos products from other manufacturers will remain available – see Table 1 for a list of alternative chlorpyrifos products available.
- Organophosphates, including chlorpyrifos, will continue to be essential for IPM of field crops: limited modes of action (MoA) are available, and organophosphates can be rotated with other MoA (e.g., pyrethroids) for resistance management.
- Consider adding sulfoxaflor (Transform®) or afidopyropen (Sefina™), two new active ingredients, to the rotation for soybean aphid resistance management.
- Watch for news regarding chlorpyrifos in the future: health concerns + declining sales + voluntary cancellations + EPA registration review in 2022 could bring unexpected changes.
- The label is the law! Follow all directions on the label for proper use. This will a) prolong efficacy, b) ensure it is safely used, and c) limit environmental and non-target effects.
Premix Active Ingredients (IRAC Group #)
Loveland Products, Inc.
Loveland Products, Inc.
Gharda Chemicals, Ltd.
Gharda Chemicals, Ltd.
Innvictis® Crop Care, LLC
Innvictis® Crop Care, LLC
Quali-Pro, ADAMA, Winfield® United, Drexel Chemical
1EC = emulsifiable concentrate; G = granules
Disclaimer: Table 1 may not provide an exhaustive list of all possible chlorpyrifos products, manufacturers, or distributors, and was updated 2/13/2020 from the Agrian Label Search service. Check with your preferred retailer for product availability or recommendations.Category: Crop ProductionInsects and MitesTags: chlorpyrifosorganophosphate insecticideinsecticidescorteva
Prior to spring field operations, ensuring your equipment is ready can save valuable time and reduce stress when windows get tight due to weather conditions. The sprayer is a critical piece of equipment in most crop production operations. Ensuring your sprayer is mechanically sound, clean, and properly setup will help ensure quality and timely applications of spring fertilizer and pesticides.Nozzle selection and setup
The spray nozzles are a critical piece of quality spray applications. Take time to look at the products you plan to apply in 2020 and evaluate if the nozzles you already have will work well with those products at the speeds and pressure you plan to operate in. Some chemicals like dicamba and 2,4-D products have strict nozzle requirements whereas other products like glyphosate allow more choices. For example, there are only four types of TeeJet nozzles approved for use with Enlist Duo herbicide (nozzle specifications on page three). When applying multiple products, refer to the label with the most strict nozzle requirements to select your nozzle for that application. If you operate at a wide range of speeds and pressures during the season you may want to evaluate the benefits of a PWM (pulse-width modulated) spray system to provide a broader range of nozzle flow rates while managing droplet size more consistently.
Running the sprayer with water to evaluate nozzle performance before the season starts is a best practice. Ensure this is done in a safe manner with proper personal protective equipment. This allows you to check the flow through each nozzle. While this can be time consuming, it helps you identify worn, plugged, or damaged nozzles. Using a tool like a Spot-On Calibrator (video available) can make this process quicker and simpler.
Nozzles with debris build up can cause significant deviations in flow between nozzles on a common rail boom setup (Figure 1). The debris will cause the affected nozzle to experience a different pressure than non-plugged nozzles on another area of the boom and create rate variation across the boom. This illustrates the importance of recognizing the quality of water you are spraying and taking appropriate measures to protect your system from debris. This might include additional strainers on the loading lines of the machine and cleaning nozzles more frequently. It’s also good to examine nozzle alignment during this process. Nozzle holders or mounts can bend or move (especially if booms frequently hit the ground or other obstructions). Proper alignment ensures the optimum spray pattern is maintained by your machine.
Figure 1. Nozzle strainers will often build up debris as a result of dirty carrier solution or chemical build-up. If left clogged this will restrict solution flow through this nozzle and impact the application rate for this nozzle.
It’s always recommended that the machine’s plumbing is cleaned regularly to avoid chemical build up and potential cross contamination. Double check these areas prior to heading to the field in 2020.
- Strainers are crucial to ensuring particulate doesn’t get into the solution system or nozzles. Regular cleaning of all strainers on the machine is always recommended. Some machines have multiple strainers on the chassis or boom. (Figure 2)
- Inspect the machine plumbing for hoses that are not properly secured, sagging, or have excess wear. Sagging or kinked hoses can impede solution flow and cause chemicals to become trapped in these areas. Replace worn hoses and tie up loose hoses.
- Remove and check the end caps on solution tubes for buildup and clean if needed.
- Depending on the type of flowmeter your system uses, remove the insert and ensure it’s clean and can move freely. (Figure 3)
- Have the flowmeter on your machine re-calibrated. Your local equipment dealer or rate control supplier can assist you with this process.
- The fencerow nozzles are typically the first to be broken on a machine due to their placement. If equipped on your machine, make sure the nozzles and plumbing are in good working order and the system is functional if you intend to use it.
- Check around fittings for any chemical residue or evidence of leaks.
- Inspect the foam marking systems if equipped. While many operators don’t use these today, they can come in handy if your machine experiences GPS problems.
Figure 2. Frequently inspecting and cleaning the main solution strainer will reduce pressure drop in the system, improve the consistency of the spray application rate, improve the life of spray system pumps, and reduce the risk of contamination when switching products.
General machine maintenance
Figure 3. Routine cleaning of the sprayer flow meter will ensure accurate application rates and reduce the calibration requirements for the solution system.
It’s important to make sure your sprayer is mechanically sound. Consult your owner’s manual for checklists and specifications to evaluate during this process. Make sure greasable parts and joints are properly lubricated, machine fluids are at the proper level, filters are clean and in good condition, and tire mounting nuts are properly torqued and in good condition. Many boom suspension components require frequent lubrication to ensure adequate movement and can have an impact on boom height control performance. Sprayer tires also are important to evaluate and check. Due to the high speeds and axle loads experienced by sprayer tires, they need to be in good operating condition and properly inflated.
Taking time to inspect and maintain your sprayer now is one step to preparing for a smooth spring.Category: Equipment and MachineryTags: sprayer maintenancesprayerssprayer nozzlespring maintenancemachine maintenance
While seasonal weather can be the difference between a good and a bad harvest, it is the soil that moderates the long-term productivity of a field. The inherent properties of soils are vital to know when it comes to management practices on any agricultural landscape.
The state of Iowa has the agricultural economy that it does largely because of its soils. Iowa relies on soil for so many different things, the list can be overwhelming at times and includes crop production, water management, and land valuation.
Iowa State University researchers are working to update Iowa’s soil survey, which was completed about 30 years ago, with small tweaks since then. Those original maps were produced by the Cooperative Soil Survey, which was a partnership between Iowa State University and the United States Department of Agriculture’s Natural Resources Conservation Service. The maps were compiled county by county and each took about four years to complete.
The existing soil maps were meant to give a general idea of the soil resources, but as we get into precision agriculture, a lot of farmers—because they don’t have a better resource—are using these maps to decide on their management zones within the field, even though the creators of these maps never intended them for that.
A statistically-based approach
The Iowa Soil Survey originally were published as books. Now they can be found online.
What we need is higher spatial detail and a more statistically-based approach in predicting soil properties. Algorithms are being developed to automatically classify parts of landscapes with different soil properties. Every landscape has some unique characteristics that need to be accounted for, and that is done through machine learning.
An algorithm recognizes patterns in these landscape characteristics and uses those patterns to make predictions for areas without soil samples. Different technologies used to gather data are being input into the algorithm to increase consistency and accuracy of the maps.
Different sources of remotely sensed information, from an airplane or satellite platform, are stacked together with many potential covariates, or predictors. This means obtaining continuous coverage of data that is expected to covary with different soil properties. The difference from the traditional soil survey methods is the large quantity of covariates and the complex, quantitative models built by machine learning.
Covariates are collected in two different ways. The first is terrain analysis. This starts with detailed elevation data that comes from an airplane equipped with LIDAR, (Light Detection and Ranging). This measures the rise and fall of the landscape and records the elevation information by shooting a laser from the plane to the ground and recording the time it takes to bounce back. The elevation data is then analyzed for the different landscape aspects that influence environmental conditions, such as water flow.
An example of a digital soil map predicting sand content.
The second method is collecting spectral information with satellites. The whole electromagnetic spectrum, both light seen by the human eye and light that can’t be seen is collected. Healthy vegetation on a landscape is directly related to the plant’s root system in the soil, thus being able to infer soil characteristics based on what it happening above ground. The big difference with the previous maps is there is now this big, new data source gained via satellite information, LIDAR information and machine learning that enhances the spatial detail of soils.
Research is still underway on finding the best covariates to use and the most appropriate machine learning algorithm to find complex patterns. While the full completion of this project relies on funding, the first version of an interactive web map for the public should be made available by the end of 2020, which will also be made available for download for GIS professionals.Category: SoilsTags: soil surveysoil typesoil mapsIowa soil survey
Iowa State University researchers recently published their annual fungicide trial data for soybeans in 2019, revealing a continued decline in efficiency among the QoI class of fungicides in preventing foliar diseases in soybeans.
Among the six Iowa State research farms — Northwest Research and Demonstration Farm (Sutherland), Northern Research and Demonstration Farm (Kanawha), Central Iowa Research Farms (Ames), Armstrong Memorial Research and Demonstration Farm (Lewis), McNay Memorial Research and Demonstration Farm (Chariton), and Southeast Research and Demonstration Farm (Crawfordsville) — the top two foliar diseases observed in the 2019 growing season were frogeye leaf spot (Cercospora sojina) and Septoria brown spot (Septoria glycines). Researchers tested 16 fungicide compounds and their efficacy in controlling these two diseases. All research locations had natural inoculum for both diseases. All fungicide applications were made at the R3 (beginning pod) growth stage, at the recommended label rate. Researchers note that the Northeast Research Farm data was not included in its results because of missing data.
Per the fungicide trial results, overall fungicidal control of frogeye leaf spot was only statistically significant at the Ames location (Table 1). The trial results among the other research farms did not illustrate a significant change in disease control with fungicide use. In analyzing individual fungicidal performance, those that contained solely quinone outside inhibitors (QoIs) had decreased efficacy in controlling the disease, compared to compounds that came in a premix containing multiple fungicidal modes of action.
Table 1. Frogeye leaf spot severity (% in upper canopy) in fungicide treatments across the six locations in 2019. Note, all fungicides are premixes except for Quadris. All products were applied at R3 with nonionic surfactant (Induce at 0.3% v/v) unless otherwise noted.
NS= Non-significant, CV = Coefficient of variance, NA = Not analyzed, LSD = Least significant difference
Overall fungicidal control of Septoria brown spot was only statistically significant at Ames, Armstrong, Kanawha, and McNay (Table 2). Similar to the frogeye leaf spot trials, fungicides that contained solely QoIs had decreased efficacy in controlling the disease compared to compounds that came in a premix containing multiple fungicidal modes of action.
Table 2. Septoria brown leaf spot index (% in lower canopy) recorded on fungicide treatments across the six locations. Note, all fungicides are premixes except for Quadris.
All products were applied at R3 with nonionic surfactant (Induce at 0.3% v/v) unless otherwise noted.
NS= Non-significant, CV = Coefficient of variance, NA = Not analyzed, LSD = Least significant difference
All sites compared fungicidal efficacy to an untreated control plot at each station. These groups contained the highest disease severity. In this experiment overall, fungicides containing more than one active ingredient performed better than the QoIs alone.
These research results confirm Iowa State findings that foliar fungal disease continues to develop resistance to QoI. Fungicides reliant solely on QoIs had decreased efficacy against both frogeye leafspot and Septoria brown leaf spot, which are the main foliar diseases of concern in Iowa, and did not provide profitable yield increases. Therefore, researchers conclude that unnecessary use of foliar fungicides should be minimized and an integrated method of disease management that does not depend solely on foliar fungicides should be employed. If a fungicide application is deemed necessary, consult a current efficacy chart like the one produced by the Crop Protection Network to select a fungicide that will control the disease of concern.
Fungicides are very important tools for disease management, and it is critical to preserve their efficacy. Other disease management practices such as crop rotation and planting of disease-resistant cultivars should be used to minimize dependency on fungicides.Crop: SoybeanCategory: Plant DiseasesTags: foliar fungicidefungicide efficacy tableQoI resistance
Iowa State University researchers, with funding from soybean checkoff through the United Soybean Board and Iowa Soybean Association, have confirmed that over 70 isolates of the pathogen Cercospora sojina (cause of frogeye leafspot in soybeans in Iowa) are resistant to quinone outside inhibitor (QoI) fungicides.Experimental design
Throughout the months of September and October of 2019, Iowa State extension plant pathologists collected soybean leaves displaying symptoms (small round lesions with dark reddish-brown borders) of frogeye leaf spot across 73 soybean fields, spanning 51 counties. Fungal spores were collected from each leaf lesion and isolated for a strain of the C. sojina pathogen. One isolate from each of the 73 fields was tested for sensitivity to azoxystrobin, a QoI fungicide. Researchers compared these test results with two control groups of C. sojina isolates with known sensitivity to azoxystrobin.Results
Resistance to azoxystrobin was classified as fungi germinating in the presence of 1 parts per million (ppm) of azoxystrobin. Researchers found that nearly all of the isolates tested from all 51 counties had some level of resistance to azoxystrobin, having higher than a 50% germination rate (a single field in Adair County did not have such a high rate). In fact, most isolates were able to germinate in 10 ppm of azoxystrobin.What does this mean?
As azoxystrobin is part of the QoI class of fungicides (FRAC Code 11), it’s important to know that the C. sojina pathogen’s isolates are most likely resistant to other fungicides within that same class, as resistance to QoIs is often the result of a single gene/single site mutation, most commonly the G143A mutation that occurs at the fungal cytochrome b gene.
Frogeye leaf spot resistance to QoIs was confirmed in Iowa back in the 2018 growing season by the Mueller Lab. The continued development of resistance among the pathogen’s different isolates illustrates that using QoIs as the primary control of frogeye leaf spot is no longer a solution to control the disease.
QoI-resistant strains can still be managed effectively with other fungicide groups, but introducing alternative disease management practices will be even more important to preserve future use of these fungicides. Selecting a frogeye leaf spot-resistance cultivar and incorporating crop rotation with non-host crops in to an operation can provide better control of the disease.
For more information about the frogeye pathogen, disease development, and the mechanisms of fungicide, please review our previous article on the subject.Crop: SoybeanCategory: Plant DiseasesTags: frogeye leaf spotQoI resistance