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Consideration for Tillage Decision this Fall After Drought

Mon, 10/19/2020 - 16:04

The dry, warmer-than-normal growing season this year presents significant challenges for managing soil and crop residue this fall.

Excessively dry soil conditions this season make field preparation and tillage this fall challenging, even though a dry soil condition is preferred for conducting tillage operations. The advantage of having low soil moisture for tillage is a reduced impact of equipment traffic in causing soil compaction and ruts in the field. However, soil disturbance under dry or any other conditions destroys soil structure and increases the potential for soil erosion after any rain events and the loss of soil organic matter, top soil, and nutrients.

The lack of soil moisture, especially in the top 12 inches where most tillage occurs, can produce unfavorable conditions for soil fracturing. The excessive dry soil conditions can produce large soil clods that are not easy to break with secondary tillage in the spring. Also, tilling excessively dry soils can be costly in terms of fuel and time use as compared to soils with normal field moisture at field capacity. The effectiveness of incorporating crop residue may be limited and the lack of moisture will reduce the breakdown of crop residue.

The best option for managing dry soils and crop residue under dry conditions is to limit soil disturbance and keep residue on the soil surface. Crop residue can help mitigate drought conditions by trapping rain and snow moisture to recharge the soil profile for the following season.  It has been documented that keeping residue standing with no-till on the soil surface can trap 70% more of the water in rain or snow melt than conventional tillage. The water storage capacity of soil will be greater than that with conventional tillage, where soil structure is destroyed. Crop residue and tillage consideration for this fall is highlighted in this article: https://crops.extension.iastate.edu/blog/mahdi-al-kaisi/residue-management-consideration-fall

Conservation practices play a major role in managing soil moisture. The absence or reduction of soil disturbance in no-till both minimizes soil moisture loss from the soil's surface and maximizes soil moisture storage. They also enhance beneficial soil physical properties such as increased water infiltration, maintenance of soil macropores, and reduction of surface runoff during rain events, thus increasing soil moisture storage.

Generally, every tillage pass can cause the loss of 1/4 inch of soil moisture. However, this number varies based on soil texture, soil organic matter content, and the amount of residue on the soil surface. Thus, with the unpredictability of weather and to insure maximum soil moisture storage, precaution should be exercised in using tillage to manage dry soils this fall, and farmers should keep residue upright on the soil surface to increase the soil profile moisture recharge.

Category: Soil ManagementTags: tillagetillage decisionsdroughtfall tillagesoilsSoil Management

Be Cautious When Interpreting Fall Soil-Test Results Following Drought

Wed, 10/14/2020 - 16:06

Sampling soil this fall following the dry conditions this past summer, and in some places continuing up to this time, may result in lower than expected soil-test results for phosphorus (P), potassium (K), and pH. Especially if soil samples are collected before any significant rainfall. Therefore, farmers and crop consultants should interpret those soil-test results with caution.

P and K removal with crop harvest

Estimates of P and K removal are used to decide fertilizer application to maintain soil-test P and K levels within the Optimum soil-test interpretation category. Prolonged drought can reduce crop grain yield and, consequently, P and K removed with harvest, so the planned removal-based rates may be reduced accordingly. However, a large yield reduction is not likely if below normal rainfall was only from late August, so in these fields the planned removal-based rate should not be reduced. Removal-based rates in fields with low grain harvest recovery from badly lodged corn due to the August or recent windstorms should not be reduced because P and K in unharvested grain will become available for next year crop. Although sampling harvested plant parts for analysis is an option, an easier and effective approach to estimate P and K concentrations per unit of yield is to use information provided in Iowa State University Extension and Outreach publication PM 1688 (A general guide for crop nutrient and limestone recommendations in Iowa). Concentration values in that publication are adjusted from a dry matter basis so they can be directly multiplied by the yield at the standard moisture concentration. For example, values from PM 1688 for corn grain at 15% moisture are 0.32 lb P2O5/bu and 0.22 lb K2O/bu; and for soybean grain at 13% moisture values are 0.72 lb P2O5/bu and 1.2 lb K2O/bu. It must be remembered that the yield level variation is by far much more important at determining nutrient removal than variation in P or K concentrations.

P and K recycling to soil

Although low rainfall since a crop physiological maturity late in the growing season may not affect yield and the amount P and K removed with harvest, it can greatly reduce the amount of plant P and K recycled to the soil. Normal rainfall leaches plant nutrients into the soil after plants mature (from standing vegetative plant parts) and from crop residue after harvest. Potassium recycling occurs earlier and faster than for P because K in plant tissue is soluble in water and plant P is mostly organic. Research has shown that with good yields and normal rainfall soybean and corn recycle about 80 and 30 lb K2O/acre of K to the soil, respectively, between physiological maturity and grain harvest whereas additional 30 and 15 lb K2O/acre are recycled, respectively, from harvest until early December. The recycled K is fully available to the next year crop. For P, the amounts of soluble P recycled are much lower, on average being only 10 and 7 lb P2O5/acre for corn or soybean, respectively, for the entire period from physiological maturity until early December.

Therefore, below normal rainfall from the time of physiological plant maturity until the time of soil sampling in the fall will result in much less K recycling to the soil than normal, and consequently lower soil-test K levels than with normal fall rainfall. A small soil-test P reduction is possible but less likely.

Effects on soil sampling and testing

With a prolonged drought, low crop yields, and low P and K removal, post-harvest soil-test P and K levels tend to be higher than expected. However, if below normal rainfall was only from late August, this effect will be small. Conversely, dry soil after crop physiological maturity slows down the normal reactions between soil nutrient pools, which often results in lower soil-test P and K levels. Plants are like pumps taking up P and K from available soil pools, but as nutrient uptake decreases late in the season, normal rainfall and moist soil allow for a replenishment of the available nutrient pools (measured by soil tests) from the less available pools. Dry soil limits soil-test rebound, and often affects soil-test K more than soil-test P. However, the greater impact at reducing soil-test K levels often comes from lack of rainfall reducing K leaching from plants to the soil.

Very dry soil conditions may result in lower soil pH values (more acidic in neutral to acidic soils). Differences ranging from 0.1 to 0.4 pH units lower are common with very dry conditions from late August until soil sampling in the fall. This is because small concentrations of soluble salts normally present in the soil solution are not leached down to deeper layers by rainfall, which results in higher hydrogen ion concentration and greater acidity (lower pH) in the topsoil. On the other hand, the dry soil effect on buffer pH, which is used to estimate lime requirement, is not large or consistent. Therefore, the main issue with pH measurements with dry soil is taking into consideration that the pH value may under-estimate pH and the decision if lime should be applied or not, but will not affect much the amount of lime to apply.

Another possible problem of sampling during dry soil conditions is that it may increase sampling error because it is more difficult to control the sampling depth and accomplish proper soil core collection. This may be especially serious in no-till and pastures, due to large nutrient stratification with depth; but stratification is also present with chisel-plow/disk tillage. When the top inch of soil is very dry and powdery, it is very easy to lose this soil portion from the core, which will affect the soil-test result significantly.

Suggestions about soil sampling and test results interpretations during drought conditions
  1. Consider yield and estimates of P and K removal with harvest during the last two years to decide maintenance fertilization rates for the Optimum soil-test category.
  2. Delay soil sampling until meaningful rainfall occurs because it will result in a better sample and more reliable soil-test results, mainly for K and pH. It is not possible to say how much rainfall is helpful, but we believe it should be sufficient to wet the soil throughout the sampling depth (usually six inches) and sampling should be delayed for at least a week after rainfall.
  3. If you still have to take the soil samples during dry conditions:
    1. Be careful with sampling depth control and that you collect the complete soil core.
    2. Soil K test results may be lower than they would be with normal conditions due to less recycling to the soil and less replenishment of the soluble or easily exchangeable soil K pools.
    3. Soil P test results probably will be affected little by the recycling issue.
    4. Soil pH test result may be lower than in normal conditions, which may encourage you to apply lime when is not needed yet. However, buffer-pH, which is used to determine the amount of lime to apply, will not be affected much.

For additional information about P, K, and pH/lime management visit the ISU Extension Soil Fertility web site at http://www.agronext.iastate.edu/soilfertility/.

Category: Soil FertilityTags: soilsfall soil testdrought

Fall is a Great Time to Sample Fields for SCN – Especially in 2020

Wed, 10/07/2020 - 09:02

Most farmers and those who advise them likely have heard that the soybean cyst nematode (SCN) is a top yield-reducing pathogen of soybean in the Midwest.  What they might not know or remember is that:

  • An estimated 70% of Iowa fields are infested with SCN
  • 30% or more yield loss can occur with no above-ground symptoms
  • Dormant SCN eggs can survive in soil for 10 years or more without soybeans
  • Most resistant soybean varieties no longer control SCN reproduction very well
What’s so special about sampling for SCN this fall?

The drought conditions that occurred throughout large parts of Iowa in 2020 may have resulted in high levels of SCN reproduction occurring in soybean fields, allowing SCN numbers to increase to very damaging levels. The link between high SCN reproduction and hot, dry soils was discovered in data from more than 25,000 research plots in Iowa State University experiments conducted over 15 years.

Sample fields where soybeans were grown in 2020

If fields have never been checked for SCN or have not been sampled before or after the last three soybean crops, the results of soil samples collected this fall after soybeans may be real eye-openers. The lack of above-ground symptoms, loss of effectiveness of resistance, and high reproduction in dry soils could have resulted in very high end-of-season population densities of the nematode this year. It is useful to know what the SCN population densities are in fields this fall even if soybeans will not be grown in these fields in 2021. Numbers may be so high that planning for multiple years of a nonhost crop might be warranted in the rotation.

Sample fields in which soybeans will be grown in 2021

Although SCN population densities would not have increased in fields where corn was grown in 2020, it is important to know what SCN population densities are present in the soil if soybeans will be grown in these fields in 2021.

Depending on the results of the soil samples, farmers and agronomists may want to search for effective resistant soybean varieties and nematode-protectant seed treatments. Data on yields and SCN control of hundreds of SCN-resistant soybean varieties in Iowa State’s SCN-resistant soybean variety trials are available online here.

If soil sample results reveal that SCN population densities are greater than 12,000 eggs per 100 cc of soil, it would be advised to grow another year of corn (a nonhost) in 2021.

Guidelines for collecting good soil samples
  • Use a soil probe (figure 1), not a spade, to collect soil cores.
  • Collect 15 to 20 8-inch-deep soil cores from every 20 acres.
  • Collect samples from management zones in the field, if possible (figure 2).
  • Combine and mix soil cores then fill a soil sample bag with the soil.
Where to send the samples for analyses

There are numerous laboratories in Iowa that process soil samples to provide SCN population densities. Most private soil labs offer this service. Also, the Iowa State University Plant and Insect Diagnostic Clinic processes samples for SCN. Click on Iowa on the map at this webpage for a list of laboratories in Iowa that process SCN soil samples.

For more management information

There is a large amount of information available online about the management of SCN. Check out www.soybeancyst.info, www.soybeanresearchinfo.com, and www.thescncoalition.com.

Figure 1. Use a soil probe to collect 10 to 20 8-inch-deep soil cores to represent a single SCN soil sample.

Figure 2. Collect separate multiple-core soil samples from different management zones within a field to account for possible differences among the areas.

Crop: SoybeanCategory: Insects and MitesTags: SCNsoybean cyst nematodescoutingfield samplesmanaging soybean cyst nematode

Combine Gathering Attachments for Lodged Corn

Thu, 09/10/2020 - 12:41

Wind damage or stalk rots can cause lodged corn that is difficult to gather with standard corn harvesting equipment. Powered attachments for corn heads are available to assist the gathering process and reduce the number of missed stalks and ears. These attachments assist the flow of corn stalks up and over the snouts and into the gathering chains and cross augers. While required travel speed may still be significantly reduced from normal, these attachments can greatly reduce head plugging and field gathering losses. This article will discuss several combine head attachments to assist in gathering lodged corn and has resources for finding these attachments.

Finger reel attachments

Finger reels consist of a horizontal rotating shaft with long (3-4 feet) slender steel bars (fingers) that rotate like a small grain reel to help move lodged corn stalks into the gathering chains and cross augers. The fingers are often in pairs for each row, offset slightly to the right and left of the row to allow passage of standing corn between the fingers. The fingertips are often curved toward the row to guide lodged stalks into the gathering chains and curved away from the direction of rotation to release the stalks as they near the cross augers. The mounting brackets allow the shaft location, both up-down, and forward-aft, to be adjusted so that the fingertips clear the gathering chains below and clear the cross augers and ear savers behind. Some models include flexible fingertip extensions to reduce the risk of mechanical damage if the fingertips contact the gathering mechanism. The mounting brackets are attached to the framework of the head.

The drive mechanism for finger reels is often a variable speed hydraulic orbital motor and chain gear reduction, allowing the operator to set the reel speed and resulting fingertip gathering speed slightly faster than the forward travel of the combine.

Kelderman Corn Reel. Photo courtesy of Kelderman Manufacturing

Paddle reel attachments

Paddle reels consist of a horizontal rotating shaft with a set of (typically 3) paddles per row, approximately 12-18 inches long and 4-8 inches wide. The paddle material and shape varies by model. These rotating paddles assist material movement up the gathering chains and into the cross augers. An additional set of paddles is often mounted at the center of the head to assist in clearing crop congestion at the feeder house entrance. Compared to finger reel attachments, the paddles set slightly lower and farther aft in the head. Paddle reels may be designed less for getting lodged stalks into the gathering chains, and more for moving tangled stalks up the stripper bars and into the cross augers. To assist in their function in variable conditions, the shaft and paddle location both up-down and forward-aft is hydraulically adjustable on-the-go. The drive mechanism is typically a variable speed hydraulic orbital motor and chain gear reduction.

Patriot Crop Sweeper paddle reel. Photo courtesy of Minden Machine, Inc.

Snout cone attachments

Snout cones consist of tapered cones with shallow (1-2 inch) helical flighting. The cones are mounted in line with, and just above the snouts. The cones rotate to use screw-auger action to lift lodged and tangled stalks up and pull them back over the snouts. The support and bearing at the front end of the cone is covered by a protective tapered hood to prevent catching of stalks.

When snout cones are mounted over every snout, they are typically driven by a horizontal shaft that is powered by a variable speed hydraulic orbital motor. The horizontal shaft powers the rear ends of all the cone axles through right angle drives. When snout cones are mounted only over the outside snouts to gather stalks lodged outside the head swath, they are typically powered with a variable speed hydraulic orbital motor connected directly to the individual cone axle.

Roll-A-Cone Corn Lifters with integrated paddle reel. Photo courtesy of Roll-A-Cone Manufacturing

Combinations of attachments

Snout cones (end snouts, or all snouts) are sometimes offered in combination with finger or paddle reels. In these cases, the drive mechanism for the reel may also power the snout cones.

Patriot Snout Cones, with integrated Crop Sweeper paddle reel. Photo courtesy of Minden Machine, Inc.


Equipment suppliers for gathering process attachments have years of experience, testing, and product refinement. While home manufacture of these types of attachments may be possible, reliability and safety are critical around gathering equipment and tested commercially available attachments are highly recommended.

Suppliers of gathering process attachments as of 2020 include the following (inclusion does not suggest endorsement, nor does omission indicate lack of endorsement, but simply difficulty in finding current contact information).

Finger Reels:

Finger Reels, Paddle Reels, Snout Cones:

Paddle Reels:

Snout Cones, Paddle Reels:

Crop: CornCategory: Equipment and MachineryTags: combineharvestEquipmentcombine attachmentslodged cornderechodowned corn

Corn Rootworm Monitoring Network Summary

Thu, 09/10/2020 - 10:22

A monitoring network was established this year to monitor corn rootworm adults in Iowa cornfields, similar to the moth trapping network we manage in the spring each year. The goal was to help farmers and agronomic professionals monitor populations of northern corn rootworm (NCR) and western corn rootworm (WCR) in their fields and assess management decisions. A secondary goal was to estimate the ratio of NCR to WCR throughout the state and describe changing ratios into the future. The sampling protocol used is detailed at the end of the article.

When using sticky traps to monitor for corn rootworm adults, you can assess management decisions based on the number of beetles per sticky card per day. Capturing greater than two beetles/trap/day suggests that something different should be done to manage corn rootworm the following growing season. For example, you may consider planting soybean the following season to manage corn rootworm. Or, if you are using a hybrid with corn rootworm Bt traits and plan to plant corn the following year, you may consider using a soil-applied insecticide instead.

Monitoring summary: 21 volunteers monitored 35 fields for four weeks beginning the week of July 13. The fields were located in 19 counties in the northern two-thirds of the state and two counties in southeast Iowa. Twenty-five fields were continuous corn, while nine were corn following soybean. Only two locations with a corn-soybean rotation planted a hybrid with corn rootworm Bt traits, while all but one continuous corn location planted a hybrid with a corn rootworm Bt trait. Locations with a corn-soybean rotation tended to capture fewer corn rootworm beetles over the trapping period (0-15) than continuous corn fields (0-533), which was expected as crop rotation is an effective management tactic for corn rootworm.

The total number of WCR and NCR captured during the peak week at each location is shown in Figures 1 and 2, respectively. It is important to note that the peak week varied by location. Adult emergence is based primarily on degree day accumulation, but emergence can also be influenced by soil factors, planting date, larval density, and whether larval corn rootworm was challenged by the presence of insecticides or Bt toxins. Since the rootworm species present doesn’t affect management decisions, Figure 3 shows the total corn rootworm beetles captured during the peak week at each location.

Figure 4 shows the ratio of WCR:NCR during the peak week at each location. A ratio greater than one indicates more WCR than NCR were reported at that location. Seven locations reported more NCR than WCR: these were located in Clay, Kossuth, Polk, Washington and Winneshiek counties. We suspect these ratios are changing, and we intend to monitor their change over time as we continue this project in the future.

We appreciate our volunteer cooperators for helping with the first year of this project. We hope to continue this monitoring effort into the future and have more participation across the state.

Disclaimer: The data we collected from individual fields cannot be used to make region-wide predictions of corn rootworm activity or density. Populations of corn rootworm are localized to individual fields and are based on past and current management practices. Corn rootworms overwinter in Iowa cornfields, and movement is typically restricted to within fields or between neighboring fields. WCR, specifically, only disperses about 130 feet (40 meters) per day.

Sampling protocol: We mailed traps to volunteer cooperators at the end of June. Cooperators established a transect of four traps, the first placed 165 feet into the field and the rest placed every 165 feet along a single row. Cooperators would return a week later, count the number of each species present on each sticky trap, and replace each sticky trap with a new one. They set their first traps in the field the week of July 13 and continued sampling for one month. We aimed to capture the peak emergence of beetles in the field, though emergence can occur for a period of 6-8 weeks. Normally, multiple transects would be established within a single field and traps would be monitored for eight weeks.

Crop: CornCategory: Insects and MitesTags: corn rootwormcorn rootworm managementinsect managementinsect monitoring

2020 Drought and Derecho Impacted Corn-Harvest, Mycotoxin Testing and Storage

Wed, 09/09/2020 - 16:50

The August 10 derecho left portions of Iowa with broken, uprooted, and damaged corn across a significant portion of the state. Paired with drought conditions across the state, especially in west central Iowa, growers should be on the lookout for mycotoxin issues in this years’ crop, especially aflatoxins and fumonisins, as discussed in “Drought and Derecho Increase Mycotoxin Risk in 2020 Iowa Corn Crop-Scouting and Monitoring Fields”. For fields that are intended to be harvested, considerations for harvest, mycotoxin testing, and storage are presented below.

Harvest and storage of moldy or damaged grain

Mycotoxin contamination is an insurable loss, but for both aflatoxin and fumonisin adjustment, the corn must still be in the field. With this in mind, after any necessary communication with your insurance, affected grain that is harvestable should be harvested and dried as soon as possible. Harvest and handling should be gentle; mechanical injury will exacerbate mold issues that started in the field. Drying and cooling the grain quickly is necessary to hinder fungal growth and further mycotoxin production. In the time between harvest and drying, mycotoxins will continue to increase.  Avoid using low-temperature or natural air drying as this just serves as an incubator for Aspergillus fungi. Dry the grain to 1-2 percentage points below what you would for sound, healthy kernels. Affected grain should be harvested, handled, and stored separately, if possible. Consider coring bins; be prepared for the core to contain higher levels of mycotoxins than the rest of the bin as mycotoxins tend to be more associated with broken, damaged and lightweight kernels and fines. The same concept would apply for fractions removed from sound grain by mechanical grain cleaners. Move affected grain out quickly as it will not store. 

Sampling and testing grain for mycotoxins

Mycotoxin contamination is often unevenly distributed among corn ears in a field and kernels on individual ears. Not only can incidence be quite variable, but the contamination levels can vary widely among individual contaminated kernels. It takes very small amounts to cause negative health effects—on the level of parts-per-million for fumonisins and parts-per-billion for aflatoxins. The low levels that must be detected, combined with the heterogeneous distribution of contamination, make sampling and testing corn for mycotoxins difficult.

Ideally, for a sample to be representative, 10 pounds of shelled corn obtained from a variety of places in the field, truck, or other lot (or decision unit) would be ground, homogenized, and sub-sampled to obtain a final test sample. If only the amount of material needed for the final test is ground, the total error in the test result skyrockets. In essence, this means that test results are highly unreliable if a representative sample, 10 pounds, is not used.  With aflatoxins, as few as 70-80 aflatoxin-contaminated kernels in a bushel (56 pounds) can limit grain end-use, so grinding a large enough representative sample is key to obtaining a reliable estimate of the true lot concentration. Samples that are too small normally give low results, with a few giving very high readings. At points of first receipt of grain from growers, buyers may use some form of rapid test, which can give results in about 20 minutes.  This may be performed on individual trucks or on composite samples representing multiple deliveries. Samples can also be sent to testing labs for analysis. A listing of some laboratories that perform fee-for-service mycotoxin analyses, including Iowa State’s own Veterinary Diagnostic Lab, can be found here.

Use of grain

At the elevator, high throughput and limited drying and storage capacities will limit testing capabilities and the ability to segregate problematic lots “on the fly”. Adjustment in the field (when possible) may help to reduce the testing burden and unnecessary commingling of potential highly-contaminated lots. Aflatoxin is an adulterant from a human and animal food safety perspective; blending aflatoxin-contaminated grain with lower- or non-contaminated grain with the purpose of lowering the overall aflatoxin level is illegal. In severe aflatoxin years, FDA has granted blending permissions for specified regions, under supervised conditions with documented and approved end-uses. At the time of writing, no portion of the state has been granted such blending permissions.

Early characterization and quantification of mycotoxin issues is key to facilitating a safe end-use strategy for contaminated grain. Mycotoxins are heat-stable and non-volatile; once in grain, they cannot be destroyed through processing or treatment. Therefore, it is important to direct contaminated grains to a tolerant end-user.

There are acceptable uses for corn having aflatoxin concentrations up to 300 ppb. These levels are given by FDA action levels which range from 20 ppb up to 300 ppb (Table 1). End uses that are particularly sensitive to aflatoxin contaminated corn include anything with human food end-use, dairy cattle (a metabolite of aflatoxin transfers into milk), and fuel ethanol producers. Aflatoxins, fumonisins, and other mycotoxins are concentrated three times in dried distiller’s grains with solubles (DDGS) relative to the level in the corn used for ethanol production. The FDA has recommended limits for fumonisin-contaminated corn used as feed ingredients in for various livestock species and poultry, and the inclusion rates of such contaminated grain in complete feeds (Table 2). Their guidance document also contains the guidance levels for fumonisins in human food products.

Table 1. FDA Action levels for total aflatoxins in animal food or animal food ingredients. Adapted from: FDA Compliance Policy Guide Sec. 683.100 Action Levels for Aflatoxins in Animal Food


Intended Use

Animal Food and Animal Food Ingredient

Action Level

finishing (i.e., feedlot) beef cattle


300 ppb

finishing swine of 100 pounds or greater


200 ppb

breeding beef cattle, breeding swine, or mature poultry


100 ppb

Immature animals

Corn and other animal food and food ingredients

20 ppb

pets (dogs, cats, rabbits, etc.) of all ages

Corn and other food ingredients and complete pet food

20 ppb

dairy animals and other animal species (including wildlife), or other uses not specified in this table; or, when the intended use is not known

Corn and other animal food and food ingredients

20 ppb

*immature animals would include, for example, chickens and ducks less than eight weeks of age; turkeys less than 12 weeks of age; goats, sheep, and pigs less than four months of age; cattle and equine less than six months of age.


Table 2. FDA Guidance levels for total fumonisins in corn and corn by-products intended for use in animal feeds. Adapted from: Guidance for Industry: Fumonisin Levels in Human Foods and Animal Feeds

Corn and corn by-products intended for:

Total Fumonisins

Equids and rabbits

5 ppm (no more than 20% of diet)*

Swine and catfish

20 ppm (no more than 50% of diet)*

Breeding ruminants, breeding poultry and breeding mink (including lactating dairy cattle and hens laying eggs for human consumption)

30 ppm (no more than 50% of diet)*

Ruminants ≥ 3 months old being raised for slaughter and mink being raised for pelt production

60 ppm (no more than 50% of diet)*

Poultry being raised for slaughter

100 ppm (no more than 50% of diet)*

All other species or classes of livestock and pet animals

10 ppm (no more than 50% of diet)*

*dry weight basis

A discussion of scouting and in-field management is avialable in ‘Drought and Derecho Increase Mycotoxin Risk in 2020 Iowa Corn Crop-Scouting and Monitoring Fields’.

Crop: CornCategory: Crop ProductionGrain Handling and StorageTags: droughtderechograin qualitycorn harvestmycotoxinsCorn diseasestestingstorage

Drought and Derecho Increase Mycotoxin Risk in 2020 Iowa Corn Crop-Scouting and Monitoring Fields

Wed, 09/09/2020 - 16:42

The majority of Iowa is currently in moderate to severe drought, with west central Iowa under the most extreme drought. As if drought were not enough, we were dealt another blow with extreme and widespread wind damage on August 10, some of which overlapped the drought area. With these events come an increased risk for ear rots and associated mycotoxins. This article will address ear rots and mycotoxins of particular concern this year, in addition to scouting methods and monitoring considerations while grain is still in the field.

Aspergillus fungi are present in Iowa corn fields, and with the drought conditions, a significant risk of aflatoxins in the corn crop exists for the first time since 2012. Aflatoxins are a group of compounds that are produced primarily by Aspergillus flavus and Aspergillus parasiticus. These fungi grow on corn in the field causing Aspergillus ear rot and are particularly prevalent under hot, dry conditions. Aspergillus ear rot in corn is characterized by powdery olive-green mold that may be found at the ear tip or scattered over kernels elsewhere on the ear (Figure 1). Like other mycotoxins, aflatoxins are of concern because they cause a number of negative health effects in livestock and poultry. Additionally, aflatoxins are carcinogenic to humans.

Figure 1. The olive green, powdery mold that characterizes Aspergillus ear rot can be seen on this corn ear.  Photo courtesy of Alison Robertson.

In certain parts of Iowa, Fusarium ear rot  (Fusarium verticillioides and Fusarium proliferatum) and, subsequently, fumonisin mycotoxins may be present in corn this year. Fumonisin production in corn is associated with warm to hot temperatures and drought conditions, especially during grain maturation. Fusarium ear rot  typically appears as a white to pink cottony mold scattered over the ear (Figure 2). Another characteristic symptom is a white starburst on the kernel surface (Figure 3), or brown discoloration of infected kernels (Figures 2 and 3).


Now is the time to scout fields for ear rots, including those that have been flattened. Choose 5-10 locations in the field and examine 10-20 ears per location, peeling back the husks to assess mold. The fungi described above (and their mycotoxins) are often associated with damaged kernels in the field, or in harvested grain, with broken, lightweight and damaged kernels and fines. Armed with this information, a grower can think carefully about the degree to which scouting results may or may not be generalized within an individual field. It may be appropriate and more useful to examine sub-units of a field, which may be determined based on the extent of damage, intent to harvest, or other factors. Mycotoxin contamination is an insurable loss, but for both aflatoxin and fumonisin adjustment, the corn must still be in the field. You should not harvest it (or take other action) until the adjuster has visited the field. Scout now, scout often, and communicate results with a crop insurance adjuster.

Figure 2. A corn ear with Fusarium ear rot symptoms mid-ear. Photo: Erin Bowers.


Figure 3. A corn ear observed in Central Iowa in late August 2020 with kernels displaying the white “starburst” effect and other Fusarium ear rot symptoms.  Additionally, while not laboratory-verified, the green mold appearing between kernels may be Aspergillus ear rot, given the weather conditions experienced in the region this growing season. Photo courtesy of Meaghan Anderson.

Crop conditions can change rapidly, especially in downed, damaged, and drought-stressed corn and with high fall temperatures during the daytime. While corn is in the field waiting to be harvested, it may continue to mold and accumulate mycotoxins. Scouting fields now and until harvest will alert growers to harvest priority or to the need for an initial or additional assessment by insurance adjusters. Take note, there is an implication here for ensuring that if testing is necessary, it is timed close to harvest as the levels in-field may continue to increase.   

A discussion of harvesting, testing, and storing the 2020 crop is avialable in ‘2020 Drought and Derecho Impacted Corn-Harvest, Mycotoxin Testing and Storage’.

Crop: CornCategory: Crop ProductionGrain Handling and StorageTags: droughtderechomycotoxinsCorn diseasescrop scoutingfungigrain quality

Sampling Downed Corn for Damage

Wed, 09/09/2020 - 16:02

The Derecho storm on August 10 left fields with varying degrees of downed corn. In the weeks following the storm, the condition of the corn plants has worsened and the quality of the corn grain appears to be deteriorating. This deterioration in quality is expected to increase with time. 

The quality of corn grain at harvest will determine whether a buyer exists in the market and the value of the grain. Do not settle insurance claims before you have the final word on value from the buyer. A projected 100 bushel per acre yield today with no one to accept it at harvest later is still a zero-value yield plus unnecessary harvest expense. This article will address key tips to sample downed corn for damage and other quality issues prior to harvest.

Determine grain quality for settlement just before harvesting the whole field. Quality of grain at harvest can be measured by obtaining a representative sample from strips or other representative portions of the field. There are standard adjustment procedures for identifying representative strips. Obtain a tank sample (field pass) by running the combine in these areas. This will also help the producer to access how well mechanical harvest will occur should they decide to harvest the whole field. Both the producer and the insurance adjuster need to agree that the sample is representative of the area to be adjusted. While ear samples are useful for in-field scouting to estimate quality, grabbing a few corn ears from different parts of the field is not a representative sample for pricing and adjustment purposes. Buyers purchase corn grain by the truck loads and not by individual ears.

Representative samples of damaged grain, as agreed between the producer and adjuster, are best submitted to an Official USDA Grader where the full grade and toxins can be determined as a Submitted Sample. Federal Grain Inspection Service (FGIS) testing is normally more accurate than the rapid tests at grain elevators, and provides better information for the buyer as well. Once the buyer agrees to accept the grain, based on the results of the submitted sample, the entire field then can be harvested without the burden of having to find a buyer for it. Before submitting the entire sample to the official grader, it may be helpful to test for moisture and test weight with the local elevator. A test weight of 45 lb/bu or less represents potential grain quality issues; and is a simpler test than getting Mycotoxins and Total Damage analysis done. Wet mills and dry mills, where corn is used in food products, may even have a higher test weight cutoff.

Checking for Bright Yellowish-Green Florescence (BYGF) under black light has sometimes been used to indicate the possibility of fungus growth which may result in aflatoxin production. BGYF fluorescence does not indicate the possibility of other mycotoxins nor a quantification of total toxins in grain. The BGYF test is a quick test and requires very little equipment; but is only as an indicator for the presence of aflatoxin. When aflatoxin is possible, this test has value as a rapid screen for whether more detailed testing should be done.

Once the test results are back on the submitted sample and harvest of the field begins, it is normally impractical to test each truck load for toxins. Elevators and processors may decide to use a periodic composite sample (10 lbs or more from a series of trucks) to prove that the average concentrations of toxins in corn received is below limits. Such samples can submitted to a federal grader for toxins while the in-house graders can check for other factors, or they can be used to check the in-house graders on all the quality factors being tested. Composite samples do not identify individual problem loads; more intensive sampling is needed if the composite samples test above market limits for that grain buyer.

Communication is very important in the process as downed corn is harvested. All involved parties need to agree on the part of the field that is representative of the downed corn, how well the sample to be submitted for testing represents the field in question, and how the test results obtained are representative of the conditions in the field. Good communication, sampling, and testing before harvesting the whole field can save a lot of time and energy; and can help in decision making if no buyer exists for the quality shown in the test results. 

Crop: CornCategory: Crop ProductionTags: downed corncorn samplesderechodroughtgrain qualitydamaged graingrain sample

Water Quality Impacts of Cover Crop Following a Drought

Thu, 09/03/2020 - 09:57

The dry conditions throughout large areas of Iowa during 2020 reminds us of Iowa’s last significant drought in 2012 and the subsequent impacts on nitrate-N levels in subsurface drainage the following spring. This article will address concerns for water quality in drought conditions and opportunities to reduce nutrient losses from fields this fall.

There is a risk of elevated fall soil nitrate levels due to dry conditions this growing season. Dry conditions affect soil N cycling in several ways. Lack of soil moisture can reduce yields and thus N export from the field. It also reduces N cycling in the soil because microbial activity slows with lack of soil moisture. These factors can result in excess residual nitrate in the soil profile after fall harvest and the potential for substantial N leaching with late fall or spring precipitation.

At drainage water quality sites near Gilmore City, Iowa and the Northeast Research and Demonstration Farm near Nashua, IA an increase in nitrate-N concentrations in drainage water in 2013 was observed, regardless of which crop, corn or soybean, was planted in that growing season. Corn was planted in 2013 at Gilmore City and soybean at Nashua (Figures 1a and 1b). Prior research data has shown cover crops can be a very effective mechanism to reduce water quality impacts after drought years. At both sites the spike in nitrate-N levels was significantly reduced with the use of a winter cereal rye cover crop. Cereal rye was drilled after fall harvest and then allowed to grow the following spring until it was terminated before corn or soybean planting.  Cover crops were terminated about two weeks before corn planting and immediately before soybean planting.

Cereal rye is particularly effective for scavenging residual N and cycling it through plant biomass. Data from Nashua shows N accumulation in aboveground rye biomass ranging from five to over 100 lbs N/ac depending on the year and cropping system. Oats, annual ryegrass, and oilseed radish are also effective N scavengers if established early enough to allow for fall growth.

There are a few things to consider when establishing a cover crop due to dry conditions this year. One is that crop harvest will likely be earlier than it has been in recent years due to early planting, fast maturation of the crop, and the derecho opening up some acres early. This may provide an opportunity to get a cover crop established and potentially get good growth this fall. However, that depends on precipitation timing and rates. Getting a cover crop established will be difficult with aerial and other broadcast seeding methods if it stays dry. Seeding with a drill provides better seed-to-soil contact and more reliable establishment in dry conditions. However, drilling requires waiting until after harvest so you will need to weigh the pros and cons of each option and decide if you are willing to risk surface application in dry areas. Cover crops can be beneficial to incorporate this fall to minimize the risk of nitrate-N loss when rainfall occurs.

Figure 1A. Annual nitrate-N concentration in the corn year at the Gilmore City Drainage Research Facility (Sources: Waring et al., 2020; Dougherty et al., 2020)

Figure 1B. Annual nitrate-N concentration in the soybean year at the Northeast Research and Demonstration Farm (Sources: Waring et al., 2020; Dougherty et al., 2020)


Waring, E.R., A. Lagzdins, C. Pederson, and M.J. Helmers. 2020. Influence of no-till and winter rye cover crop on nitrate losses from tile-drained row-crop agriculture in Iowa. Journal of Environmental Quality 49:292-303

Dougherty, B.W., C. Pederson, A.P. Mallarino, D.S. Anderson, M.L. Soupir, R.S. Kanwar, and M.J. Helmers. 2020. Midwestern cropping system effects on drainage water quality and crop yields. Journal of Environmental Quality. 49:38-49

Crop: Cover CropCategory: Crop ProductionTags: water qualitycover cropsdroughtdry conditions

Cover Crop Options to Consider for Damaged Crops this Fall

Thu, 08/27/2020 - 11:48

Many fields have been ravaged by adverse weather this year in Iowa. On top of drought and hail we had a devastating derecho steam-roll a wide swath of Iowa starting in Sac County and progressing eastward along Highway 30. Along with the decision of how to handle this year’s crop, consideration for protecting the soil and preparing for next year’s crop should include cover crops.

Use of cover crops after a crop is damaged by adverse weather can provide short term protection of the soil while enhancing the long-term benefits of increased water infiltration, improved nutrient cycling and soil organism diversity. Using a cover crop to scavenge nitrogen will be especially important in areas of Iowa that experienced reduced yields due to drought conditions. Cover crops have shown a significant reduction in nitrogen loss from fields the year following a drought.

Successful cover crop establishment will require managing the damaged crop residue to allow seed-to-soil contact and also considering the likelihood of sufficient soil moisture for cover crop establishment.

Cover crops and moisture concerns

Cover crops need moisture to germinate, soil to root in and sunlight to grow. Timing and method of cover crop seeding will be critical this year for successful cover crop establishment, especially given the expanding drought. Moisture is always a consideration for timing of seeding, this will be no different this year for all parts of the state. The decision on method of seeding; aerial, broadcast, broadcast/incorporate or drill, will be more important than ever this year.

Moisture concerns are not only to get the cover crop established but also for next year’s crop. It has been proven that good cover crop growth will increase infiltration rate, allowing more rainwater to be captured by the soil during rain events. Terminating the cover crop earlier in the spring will conserve accumulated moisture if rain shortfalls continue through spring.

Cover crops and damaged crops

Best management practices for wind damaged corn should be based on severity of the damage and how, or if, the crop will be harvested. Fields flattened by wind or with a high degree of green snap will have varying degrees of dense leaf cover. Evaluate fields prior to aerial seeding for confidence in getting the seed in contact with soil. In most cases aerial application over these fields would be an acceptable method but considerations must account for planned method and timing of harvest.

For fields that will be unharvested and tillage will be used to size residue, seeding a cover crop after the tillage operation will provide soil cover and protection. Timing of planting will dictate what cover crop species are best suited to be planted. If the tillage is done prior to mid-September, a mix of non-winter hardy species will provide fall protection and will not need to be terminated in the spring. Winter hardy species are a great option anytime in the fall and will extend benefits of living roots and soil cover into the spring. Seeding dates vary across the state based on historical frost dates but anytime seeding is past mid-September, a winter hardy species is recommended.

For fields planned to be harvested for silage or baled, seeding the cover crop immediately after harvest will provide the best establishment window.

Harvesting downed corn pushes the limitations of both equipment and operator. Seeding a cover crop too early could provide enough cover crop growth to further visually impede harvest. Seeding after the crop is harvested with a drill to get good seed-to-soil contact will increase chances for successful establishment of the cover crop. Consider how the crop will be harvested along with severity of damage when deciding what cover crop species, method and timing of seeding will be used.

Seeding options

Aerial/broadcast application should be timed 10 to 14 days prior to the canopy opening up. This is when soybeans have 10-20% of the leaves in the upper canopy turning yellow. For corn planned for grain harvest, this will be when kernels are at half milk line (mid R5). Increased success with establishment will occur if moisture is received within 10 days of the aerial application. Use of aerial application on damaged corn needs to take into account planned harvest method and current level of soil exposed.

Drilling or broadcast with incorporation always provides the most consistent cover crop stand. A drawback to this method is the shortened time for fall growth of the cover crop but using a winter hardy cover crop like cereal rye or triticale are good options to consider. Physical disturbance of corn ears on the ground will promote germination of volunteer corn.

Management of fields with downed corn will be a challenge, but it does not eliminate the opportunity to seed cover crops yet this fall.

Crops: CornCover CropCategory: Crop ProductionTags: cover cropsdown cornderechostorm damagefall cover crop

Harvest and Storage of Weather-damaged Corn for Silage

Tue, 08/18/2020 - 11:32

Extreme weather events may lead to a decision to make corn silage rather than harvest corn for grain, or to harvest acres that will exceed current silage storage capacity. Before harvesting for silage, make sure you have a market for the silage or a sufficient number of livestock to feed it to. It may be difficult to harvest good quality corn silage if the crop has weather damage and the economic value of the silage will likely be lower than silage from non-damaged fields. The resources section has links to information that can help with pricing forages in the field and determining the economic value of corn silage.

When harvesting lodged corn for silage, use a Kemper head if possible. If a row crop head is used, flattening the head angle may help with feeding lodged corn into the forage harvester. Harvesting against the direction in which the crop is leaning and running the head as close to the ground as possible can also help. In situations where immature or drought-stressed corn is being harvested, there is potential for high nitrate concentrations in the silage. High nitrate levels can be managed by increasing the cutting height or by diluting it in the feed ration. If high nitrate concentrations are a concern, submit a sample to a forage testing lab before it is fed to livestock.

Storage options

The keys to good silage storability are harvesting at the correct moisture level, achieving good packing density, proper installation and maintenance of silage covers, and selecting a good location for storage. With unplanned silage harvest, flexible storage alternatives are needed.

Silage bags

Silage bags are a good option for storing corn silage. They allow for flexibility in both storage capacity and location. The preferred moisture range for bagged corn silage is 60 to 70%. Exceeding 70% moisture may lead to seepage, nutrient loss, and spoilage. Bagging silage that is too dry can cause uneven packing and lead to poor fermentation. Bags should be inspected regularly for holes and repaired immediately with bag tape if damage occurs. Placing bags away from trees and mowing vegetation around the bag can help prevent damage from animals. A link to more details for managing forage in silo bags can be found in the resources section.

Drive-over piles

Drive-over piles are a relatively inexpensive option for storing large volumes of silage. A moisture range of 65 to 72% works well for corn silage in drive-over piles. The key to making quality silage in piles is achieving good packing density. Spoilage losses can exceed 30% in poorly constructed piles. Unpacked piles are not an economical storage option. Silage should be placed in 6-inch layers and thoroughly packed with heavy machinery equipped with a front-end loader or push blade. As a general rule of thumb, you can multiply the estimated tons per hour delivered to the bunker by 800 to get the pounds of packing weight needed. Pile slopes should be no greater than 3:1 to minimize the risk of equipment rollover during filling. Use tractors equipped with rollover protection and seat belts for packing. Piles should not be higher than the feedout equipment can safely reach. Excessive pile height leads to silage overhang and potential collapse of the silage face. This is a serious safety hazard that may lead to injury or death.

High-capacity forage harvesting equipment and sufficient packing capacity will be needed in order to make large piles quickly. Ideally, piles should be built and covered the same day to avoid spoilage losses from the exposed silage surface. The pile should be covered with plastic and sealed along the sides by piling soil or other heavy fill material on top of the plastic. Tires, sandbags, or other weights that will not puncture the surface can be used to secure the plastic. Poorly secured plastic will lead to spoilage and is subject to wind damage. Rope can be stretched between weights to help secure the plastic if there are not enough weights to cover the entire surface. Leaving the pile uncovered will result in substantial spoilage losses that likely exceed the cost of purchasing and installing a cover. More information on pile sizing, construction, and feedout techniques can be found in the resources section.

Trench silos

An alternative to pile construction is a trench design. In areas with -suitable topography, short sidewalls can be constructed by excavating into a hillside. Sidewalls should be sloped outward from the bottom and height should be kept to a minimum. Walls should never be excavated vertically as this can lead to sidewall collapse. Lining the sides with plastic before filling will reduce spoilage losses and improve feed quality. Sidewalls must be able to withstand lateral forces from both silage and packing equipment. Attempting to construct temporary bunker sidewalls out of round bales or other unsecured materials is not recommended. Unsecured or poorly engineered walls are a serious safety hazard -that can fail rapidly and lead to equipment rollover.

Site Selection and Preparation

Good site preparation is critical for reducing spoilage and feedout losses. Select a location that allows water to drain away from the site. Do not locate bags or piles in a low area that may become inaccessible during wet conditions. Digging a shallow trench around the upslope area can help to divert surface water away from the site. A well-packed pad constructed with a 6-inch layer of 1.5 to 2.5-inch diameter gravel under a 3-inch layer of limestone screenings makes an acceptable base for year-round access. For temporary storage, placing bags or piles in a field or grassed area is an option. However, equipment traffic during pile feedout on a site without a constructed base is likely to create ruts and mud holes during wet weather. Feeding out during cold weather can help, but the ground underneath piles will not freeze and may turn to mud. Investing time into site selection and preparation will help make temporary storage a success.


Determining the economic value of corn silage.
Ag Decision Maker: Pricing forages in the field.
Tips for determining moisture of immature corn silage.
More information on making quality corn silage.
Recommendations for managing forage in silo bags.
Information on drive-over silage pile construction.
Disaster Recovery: Managing immature crops for grain or silage.

Crop: CornCategory: Grain Handling and StorageTags: silagecorn silagedown corndamaged cornderechohigh windsstorm damagesilage optionssilage bagssilage piles

Silage Harvest of Drought-Stressed and Severely Lodged Corn

Tue, 08/18/2020 - 11:23

The decision to chop corn for silage should be made when there is no further potential to increase grain dry matter and whole plant moisture is in the proper range for the storage structure. The proper harvest moisture content is the same for drought stressed and normal corn. Recommended whole plant moisture contents are 65-70% in horizontal silos (trenches and bunkers), 60-70% for bags, 60-65% for upright stave silos, and 50-60% for upright oxygen limiting silos.

Randomly sample stalks from the field and test for whole-plant moisture of chopped corn to assure that proper fermentation will occur. Using a chipper-shredder and forced air dryer is the preferred method of determining moisture (Koster, Best Harvest). Other methods include an oven, microwave, electronic forage tester or NIR.

The whole plant yield of severely lodged or broken corn at milk, dough or initial dent stages are about 65%, 75% and 85%, respectively, compared to fully dented ½ milk-line corn. The energy value of late-milk to dough stage corn is about 80-90% of normal corn silage. Feed value of drought stressed corn with ears (+40 bu/A) has about the same pound for pound value as normal corn silage. It has increased sugar content, higher crude protein, higher crude fiber and more digestible fiber than normal corn silage. Drought reduces yield and grain content resulting in increased fiber content, but this is often accompanied by lower lignin production that increases fiber digestibility.

Depending upon farm forage needs, raising the cutter-bar on the silage chopper reduces yield but increases quality. For example, raising cutting height reduced yield by 15%, but improved quality so that milk per acre of corn silage was only reduced 3-4% (Lauer, Wisconsin). In addition the plant parts with highest nitrate concentrations remain in the field (Table 1).

With lodged corn, raising the cutter-bar may not be an option. The lower part of the plant is highest in nitrate concentration. The only way to know the actual composition of drought-stressed corn silage is to have it tested by a commercial feed testing laboratory to estimate nitrate concentration and nutritive value for livestock. During silage fermentation the nitrate concentration usually decreases by one-third to one-half, therefore sample the forage after the ensiling process is complete. Table 2 provides interpretation of laboratory results for nitrate tests. Silage with high nitrate levels can be managed by dilution with other feeds.

During the ensiling process, if the plants contain nitrates, a brown cloud may develop around your silo. This cloud contains highly toxic gases and people and livestock should stay out of the area.

Some of the drought area was hot (>86oF) and dry during pollination which is favorable for Aspergillus infection. This was followed by >80oF daytime along with >70oF nighttime and drought during grain fill which is favorable for Aspergillus development. The Aspergillus fungus may produce the aflatoxin mycotoxin as kernel moisture decreases, with the highest production occurring at 18-20% kernel moisture. Most corn silage is harvested at 40-50% kernel moisture, so there is less chance of problems with aflatoxin, but the silage should be tested before feeding.


Corn Silage Harvesting and Storage, University of Wisconsin

Use of Inoculants in Corn Silage, Kevin Panke-Buisse, University of Wisconsin

Managing Immature Crops for Grain or Silage -- Disaster Recovery, Mark Licht, Steve Barnhart, Roger Elmore, Mark Hanna and Lori Abendroth

Nitrate Toxicity, Steve Ensley and Steve Barnhart, Iowa State University

Strategies if Milk is High in Aflatoxin, Mike Hutjens, University of Illinois

Aflatoxin M1 in Milk, Jodie Pennington, University of Arkansas

Crop: CornCategory: Crop ProductionTags: silageharvestdown cornlodged cornderechohigh wind damagecrop damage

Wind Damaged Corn – Nutrient Content?

Mon, 08/17/2020 - 15:44

The August 10, 2020 high winds (derecho) caused lodged or flattened corn in many Iowa fields. The corn development ranged mainly from stages R3 (milk) to R5 (dent). Some fields may not be harvested, some chopped for silage, and some harvested for grain. Nutrients such as nitrogen (N), phosphorus (P), and potassium (K) remaining in the field may be different than with normal harvest due to partial plant removal, grain harvest, or grazing. Therefore, adjustments can be made for future fertilizer or manure applications.

Effect of corn development stage

Iowa State University and Outreach publication PM 1688 (A General Guide for Crop Nutrient and Limestone Recommendations in Iowa) provides P and K concentrations for corn normally harvested for grain and corn silage. Additional information on dry matter and nutrient content of various corn vegetative components at maturity can be found in ICM News article Dry Fall Conditions Can Lead to Field Fires.

The corn plant P and K concentrations, as well as the N and dry matter concentrations, may differ with earlier growth stages. A recent ISU research study conducted across two years looked at the dry matter and nutrient content of several era corn hybrids. The following information is taken from the most modern hybrids in that study. Plant dry matter and nutrient content increases as reproductive stage and grain fill progresses (Tables 1 and 2). These values can be used as estimates/adjustments for the corn stage in specific fields. There tends to be nutrient loss from vegetative tissues as corn reaches maturity (R6 stage), therefore the total plant relative values are based on the total at R5. Such nutrient loss does not occur for grain, therefore, the grain relative values are based on the total at R6.

Total corn plant dry matter and nutrient uptake varies by productivity (yield level) and specific growing conditions (weather, hybrid, etc.). Tables 3 and 4 list the dry matter and nutrient content for the hybrids’ grain yield of 224 bu/acre. Of course, estimated nutrient amounts should be based on each field yield or harvested plant component and yield.

Key points

  • With normal corn silage or grain harvest, considerations for nutrient management and application rates for the next crop will not be different compared to a normal year.
  • For plant harvest at corn stages not normal for silage or grazing, P and K concentration estimates can be adjusted based on the growth stage. However, estimating the amounts of P and K remaining or removed will be difficult and uncertain with partial plant harvest or grazing.
  • If the corn plants are broken off and die, and plant parts are not removed or grazed, then dry matter yield and P and K concentrations can be approximated based on the growth stage when killed (see Tables 1-4); and the P and K amounts remaining in the field will be available for future crops.
  • Nitrogen remaining in non-harvested plant material will cycle through the soil system. If fields are rotated to soybean next year, changes in N recycling will not affect the soybean crop. If there is no plant material harvested, then there is potential for more than normal amounts of N to be available to next-year’s corn crop. However, that estimation should not be taken into account until the spring of 2021 as there needs to be time for N mineralization and there can be rapid change in inorganic-N (specifically nitrate) from late summer to the next spring.
Crop: CornCategory: Crop ProductionSoilsSoil FertilityTags: damaged cornderechohigh windsweather damagecrop nutrientsplant dry mattercorn development

Expectations for Lodged Corn

Mon, 08/17/2020 - 10:15

Derecho. Another of those words we wished we hadn’t heard in 2020 but are quite certain we won’t forget about the results from its occurrence. Millions of corn acres were damaged, and there are many questions about the lasting impact.

In cornfields, what did it leave behind? The damage varies considerably, but for this article, let’s break injury into three categories:

  • Plants that are only slightly root-lodged or leaning at a 45° or greater angle.
  • Plants that are pinched over but not wilted yet, broken above the ear, or severely root-lodged (<45° angle) and laying on the ground or near the ground.
  • Plants that are broken off below the ear and are now wilting or dead above the breakage site.
Effect of root lodging at >45° angle on corn

There is research that looks at impacts of lodged corn on yield, however, most was done on corn before or shortly after tasseling. Most of this year’s affected corn is in the dough stage (R4), or even early dent (R5). Carter and Hudelson (1988) from the University of Wisconsin conducted a study where they manually pushed the base of corn plants perpendicular to row direction to cause root lodging. They noted that within two days after lodging, the upper portion of plants became upright and subsequent timing of plant development was not impacted. However, more barren plants were observed when lodging occurred at later development stages, impacting yield. Corn lodged after V17 resulted in a 12-31% yield reduction. There are a couple distinctions to consider. The ability of corn plants to recover and become upright is much less likely when plants are lodged at the R4-R5 stages than in the late vegetative or early reproductive stages. Yield loss would be more when lodging at V17, since there is 0% of the grain dry matter accumulated at that time. Grain dry matter at R4 is about 20%, and at the beginning of R5 it is 25% (see ISU Extension and Outreach publication PMR 1009, “Corn Growth and Development”). Availability of moisture, severity of root system damage by lodging, and other issues can impact the extent of yield loss in this situation.

Effect of pinched stalks, broken stalks above the ear, and severe root lodging

Kinks in stalks restrict movement of resources within the plant, similar to kinking a hose while filling a water tank. If all plants are flat and still rooted into the soil, certainly they are not intercepting as much sunlight and therefore not filling grain as normal. If roots were damaged significantly and it continues to be dry, additional yield reductions will occur because nutrient and water uptake efficiency will be compromised. Plants with broken stalks above the ear will continue to produce photosynthates using intact leaves, but the available resources to fill grain will be greatly limited. Best-case scenario would be the yield loss mentioned above, with more yield loss possible based on these other potential issues. Test weight will also be compromised. Additionally, these stresses might cause premature death of some plants. Hopefully, they continue to live and produce marketable grain, although they will mature at a slower pace.

Plants broken off below the ear

These plants can no longer add dry matter to the grain, so we are left with about 25% of the potential dry matter accumulated. Test weight will be very low, and the ability to store grain killed in the dough stage is extremely limited, if at all possible. If you made it to the early dent stage, yield loss is still likely over 40%, and test weight and storage capability remains very low. The best use is silage, if a use for that much silage can be found and it can be properly ensiled.

All this discussion deals with is what happens to the ear on the stalk. Future ICM News articles will discuss the problems and some suggestions for harvesting this compromised corn, and dealing with potential grain quality issues.

Crop: CornCategory: Crop ProductionTags: lodged corndown cornstorm damagehigh windsderechocorn damageweather event

Using Cereal Rye Cover Crop and Narrow-Row Soybean to Manage Herbicide-Resistant Waterhemp

Thu, 08/06/2020 - 10:06

Waterhemp control is an increasing challenge for soybean producers due to the evolution of multiple herbicide-resistant populations. With dwindling herbicide resources, there is a need to integrate non-chemical strategies into current weed management programs in soybean. Cereal rye is the most common cover crop grown in the Midwest due to its winter hardiness and short life cycle. The high C:N ratio of cereal rye compared to legume or brassica cover crops results in a slow degradation of the residues; thereby, increasing the duration of weed suppression. This along with a greater biomass accumulation makes cereal rye an ideal cover crop candidate. Another non-chemical, cultural strategy to suppress weeds and complement herbicide efficacy is the use of narrow-row vs. wide-row soybean. Growers need research-based information on how to best integrate these two strategies for managing herbicide-resistant waterhemp in soybean.

A field study was conducted (2019-2020) at the ISU Research and Demonstration Farm near Ames, IA to quantify the impact of cereal rye cover crop and soybean row spacing (15 inch vs. 30 inch) on the glyphosate-resistant waterhemp seed bank. The previous crop was corn, with three levels of waterhemp control achieved by:

  1. A marginal herbicide program (two herbicide sites of action); 27 fl oz/acre Dual II Magnum PRE followed by 32 fl oz/acre Roundup PowerMAX POST.
  2. An aggressive herbicide program (three herbicide sites of action); 2 fl oz/acre Sharpen + 2.5 fl oz/acre Zidua SC PRE fb 32 fl oz/acre Liberty SL + 23 fl oz/acre Dual II Magnum POST.
  3. An aggressive integrated program (three herbicide sites of action) plus harvest weed seed control at corn harvest (no weed seed input).

The three programs resulted in three different levels of weed seed production.

After corn harvest, cereal rye was drill seeded (60 lb/acre) in the 2nd week of October, 2019. Soybean (Enlist E3 beans) was planted into the standing rye cover crop at a 30-inch or 15-inch row spacing on May 22, 2020. On the same day, cereal rye (at anthesis stage) was terminated with 32 fl oz/acre Roundup PowerMAX, and 27 fl oz/acre Dual II Magnum was applied to provide early-season residual control of waterhemp. Cereal rye biomass at the time of termination averaged 4600 lb/acre. To examine the potential of cover crop and narrow row soybean on waterhemp control, no POST herbicide was applied in the soybean phase of the study.

The aggressiveness of the prior year’s corn herbicide program had a strong impact on waterhemp infestation in the soybean crop. Waterhemp emergence in soybean was reduced by 75% with the aggressive two-pass herbicide program (three sites of action) plus harvest weed seed control compared with the marginal herbicide program in the previous year (Figure 1). The rye cover crop reduced waterhemp emergence (density) by 30% and waterhemp growth (size and biomass) by up to 75% through July (Figure 2). Reducing the soybean row spacing from 30 to 15 inches reduced waterhemp emergence by 15% and waterhemp growth by 50%. (Figure 3).

The integration of these tactics (Figure 4) resulted in a significant suppression of waterhemp even with limited herbicide inputs in the soybean phase of the rotation. For instance, an aggressive weed control program in corn followed by a rye cover crop and narrow-row soybean showed 87% less waterhemp emergence, compared with the treatment that had marginal weed control in corn, no cover crop and 30-inch soybean row spacing. Soybean yield will be recorded at harvest in the fall 2020 to determine the effects of cover crop, row spacing, and weed competition.

The ISU Weed Science program is also researching cover crop termination timing by herbicide interactions to develop integrated weed management tactics and methods to integrate harvest weed seed control technologies to manage herbicide-resistant waterhemp in Iowa soybean production.

Disclaimer: This article is for education purpose only. Mention of a specific product should not be considered as approval, nor should failure to mention a product be considered disapproval. Read the product label before using any herbicide.

Figure 1. Waterhemp density in soybean with marginal (left) vs. aggressive weed control program plus harvest weed seed control (right) in previous year’s corn.

Figure 2. Waterhemp density in soybean in the absence (left) vs. presence (right) of a cereal rye cover crop terminated at the anthesis stage.

Figure 3. Waterhemp density in soybean planted in 30-inch (left) vs. 15-inch (right) wide rows.

Figure 4. Effect of integrating cover crop and reduced row spacing on waterhemp density in soybean.


Crops: SoybeanCover CropCategory: WeedsTags: cereal ryeCover cropSoybeanwaterhempweed suppression

Scout Now for Palmer Amaranth

Tue, 07/28/2020 - 15:52

This is the time of year to begin scouting for Palmer amaranth (Amaranthus palmeri) in Iowa crop fields. While Palmer amaranth has been identified in more than half of Iowa’s counties, new identifications have waned since the widespread introductions in 2016. Palmer amaranth is still a species to watch out for in every Iowa crop field. Minnesota recently reported finding the weed in a county previously not known to have infestations – thus the weed is still on the move. A native of the American southwest, Palmer amaranth is more competitive than common waterhemp (Amaranthus tuberculatus), a pigweed native to Iowa. Both species are known for fast development of herbicide resistance, prolific seed production (>500,000 seeds possible), and prolonged emergence.

The addition of Palmer amaranth to Iowa’s noxious weed law as of July 1, 2017 highlights the importance of this weed to Iowans and its potential impact on Iowa agriculture. Early identification is key to eradicating this weed from fields. Eradication cannot happen without vigilance, early detection, and appropriate response soon after it invades an area. Palmer amaranth is reaching the stage where distinguishing it from waterhemp is much easier due to the presence of flowers. In addition to fields where Palmer amaranth was found previously, other priority areas to scout include farms that utilize feed and bedding from southern states, fields receiving manure from those farms, and farms where out-of-state equipment has been used.

Palmer amaranth and waterhemp lack pubescence (hair) on stems and leaves, while other common amaranth (pigweed) species have hair on stems or leaves. Early in the growing season, Palmer amaranth is difficult to differentiate from waterhemp due to the high variability in both species. Leaves on Palmer amaranth often have a petiole longer than the leaf blade, this is the most reliable vegetative trait to differentiate the two species. Leaves on Palmer amaranth are often clustered tightly at the top of the plant. Palmer amaranth often has a denser canopy than waterhemp (Figure 2).

Figure 1. Palmer amaranth leaf with a petiole longer than the leaf blade. Folding the leaf over at the base is the fastest way to check for this trait.

Figure 2. Waterhemp's open canopy (left) compared to Palmer amaranth's denser, leafy canopy (right).

Palmer amaranth and waterhemp produce male and female flowers on separate plants. Identifying males from females should be relatively simple due to the small, black seed produced by female flowers and the presence of pollen on male plants. Female Palmer amaranth are easy to distinguish from waterhemp due to long, sharp bracts (Figure 3) surrounding the flowers (Figure 4). If you discover this weed, steps should be taken to remove all female plants to prevent seed production.

Figure 3. Comparison of a female Palmer amaranth flower and a female waterhemp flower.


Figure 4. Female Palmer amaranth with long terminal inflorescences.

Continued vigilance is imperative to slow the speed with which Palmer amaranth invades our state. If you observe a plant that you think may be Palmer amaranth, please don’t hesitate to contact Bob Hartzler at 515-294-1164 or hartzler@iastate.edu or Meaghan Anderson at 319-331-0058 or mjanders@iastate.edu.

Category: WeedsTags: palmer amaranthPalmer amaranth identificationscoutingWeedsweed scouting

Unsolicited seed packages in mail

Tue, 07/28/2020 - 11:56

Most people are probably aware of the unsolicited mailing of seed packets from China and other countries. The Iowa Department of Agriculture and Land Stewardship (IDALS) has issued guidelines on how to deal with the situation if you should receive one of these packages.  The following statement was made by IDALS.

Why do we care?

1.       The seed is unlabeled, and could be an invasive plant that does not currently exist in the US.
2.       The seed may contain seed-borne diseases that we don’t have in the USA.
3.       Some packets appear to have an unknown seed treatment applied (seed treatments are usually an insecticide and/or fungicide).  Because the packets are unlabeled we don’t know what the compounds are, nor how dangerous they could be to human health.
4.       Seed is an agricultural commodity that is regulated for quality and content by the USDA as well as State Departments of Agriculture.

We are asking you to do the following:

1.      Do not plant the seed;
2.      Do not open the packets;
3.      Please let the Iowa Department of Agriculture and Land Stewardship know you have received the seed; IDALS – (515) 281-5321
4.      Please retain the packaging and seed, as we will make arrangements to collect the seed for investigative purposes and then arrange for appropriate disposal.

Why do we think this is happening?

We think this could be a brushing scam where for whatever reason they are using seed, and sometimes, packages that contain nothing. We suggest changing your passwords in your online shopping accounts.

IDALS Press Release. July 28, 2020

Category: WeedsTags: invasive weedsunsolicited mailingsregulatory

Planning a Late Summer Perennial Forage Seeding?

Thu, 07/23/2020 - 11:52

Late summer can provide a window of opportunity to seed perennial forage legumes and grasses, whether you want to establish a new forage crop or need to fill in bare and thin spots in an existing forage stand. To help improve the chances for a successful late summer seeding of forages, consider the following.

Field preparation prior to seeding

  • It is suggested to take soil samples and fertilize based on fertility needs of the field. Testing is the only way to really know the fertility levels and needs in a field.
  • Have problematic weeds under control.
  • Check herbicides used previously in the field as many can have residual soil activity that could prevent establishment of new forage seedings if the crop rotation restriction intervals are not observed. A good resource to check herbicide labels is www.cdms.net/label-database.

Timing of seeding and environmental conditions

  • Ideally, we want 6 to 8 weeks of growth after emergence before we have a killing frost in the fall; therefore, the recommended window for late summer forage seedings ranges from early August to early September, but it varies slight depending upon location in the state as listed below.
    • Northern Iowa: Early to mid-August
    • Central Iowa: Mid-August to late August
    • Southern Iowa: Late August to early September
  • One of the biggest challenges with late summer seedings is having adequate moisture available for germination and seedling establishment. This is especially a concern for western Iowa this year. If conditions are dry, a late summer seeding is not recommended.

Seedbed preparation

  • Loose seedbeds dry out very quickly. Deep tillage should be completed several weeks ahead of seeding so rains can settle the soil before final seedbed preparation. A cultipacker or roller is an excellent last-pass tillage tool. The soil should be firm enough for a footprint to sink no deeper than 3/8 to 1/2-inch.
  • If moisture is a concern, interseeding and no-till forage seeding can help conserve moisture, provided weeds are controlled prior to planting.
  • Seeding depth is important since most forage species are small-seeded. Final seed placement should be no deeper than ½-inch for heavier soils and ¾-inch for lighter soils. If seeding with a drill, it is recommended to set the drill at the ¼-inch depth. You should see approximately 10% of the seed visible on the soil surface. If you are seeing a smaller amount, the seed is being placed to deep, and you need to adjust your seeding depth.

Other considerations

  • Thickening up alfalfa stands with more alfalfa is only recommended within 12 to 15 months of the original planting date due to autotoxicity.
  • If seeding a legume, make sure the legume seed has fresh inoculum of the proper rhizobium.
  • Do not harvest late summer perennial forage seedings this fall. It is best to let them establish and develop winterhardiness.

Late summer can be an excellent opportunity to thicken up forage stands or start new seedings; however, use the above tips to help ensure success. For more information on late summer forage seeding or to get specific questions answered, please reach out to your local Iowa State University Extension and Outreach field agronomist.

Crop: Biomass and ForageCategory: Crop ProductionTags: late summer seedingalfalfaperennial grasses

Scouting reminders for spider mites

Mon, 07/20/2020 - 12:01

As parts of Iowa enter severe drought on July 14 (D2, US Drought Monitor), I encourage you to scout for twospotted spider mites in crops. Twospotted spider mites can increase whenever temperatures are greater than 85°F, humidity is less than 90 percent, and moisture levels are low. These are ideal conditions for the twospotted spider mite and populations are capable of increasing very rapidly.


A hand magnifying lens is recommended to scout for twospotted spider mites (< 1/60 inch long). They can be mistaken for specks of dirt with the naked eye (Photo 1). Twospotted spider mite larvae have six legs, whereas nymphs and adults have eight legs. Mites can be collected by shaking leaves onto a white piece of paper, and then look for moving mites. Twospotted spider mites are typically a cream or green color when feeding on corn or soybean. They can also be an orange to red color when conditions are unfavorable for their growth.

Photo 1. Twospotted spider mite. Photo by Frank Peairs, www.ipmimages.org.

Twospotted spider mites often aggregate at the field edges, especially if there are weeds surrounding the border. Eventually they may disperse with the wind to develop a field-wide infestation. I encourage people to look at the edge rows first to see if mites can be found. If their presence is confirmed, then estimate populations throughout the field by walking a “Z” or “W” pattern.

Twospotted spider mites begin feeding on the bottom of the plant, and move to the top as the plant’s health deteriorates. Although they lack wings, twospotted spider mites disperse with the wind to move from dying plants to areas with healthy plants. Therefore, it important to scout healthy areas of an infested field that are downwind from damaged areas. Symptoms of twospotted spider mite injury will initially appear as small yellow dots or stipples on the lower leaves of the plants. Prolonged feeding will cause infested leaves to turn completely yellow, then brown, and eventually the leaf will die and fall from the plant. Webbing often is visible on the edges and underside of leaves, and is an indication of prolonged colony feeding (Photo 2). Twospotted spider mites are capable of reducing soybean yield by 40-60 percent when left untreated.

Photo 2. Heavy twospotted spider mite infestation on corn. Photo by Adam Sisson, Iowa State University.


Exact treatment thresholds for spider mites in corn and soybean do not exist. Instead, the decision to treat should take into consideration how long the field has been infested, mite density including eggs, mite location on the plant, moisture conditions and plant appearance. A general guideline for soybean is to treat between R1-R5 (i.e., beginning bloom through beginning seed set) when most plants have mites, and heavy stippling and leaf discoloration is apparent on lower leaves (Photo 3). Foliar insecticides are recommended in corn from R1-R4 (i.e., silking through dough stage) when most plants have mites at or around the ear leaf and 15-20 percent leaf discoloration.

Photo 3. Twospotted spider mite injury on soybean. Photo by Whitney Cranshaw, www.ipmimages.org.

Bruce Potter and Ken Ostlie (University of Minnesota) developed a rating scale to help make treatment decisions:

0 – no spider mites or injury observed

1 – minor stippling on lower leaves and no premature yellowing observed

2 – stippling common on lower leaves and small areas on scattered plants with yellowing observed

3 – heavy stippling on lower leaves with some stippling progressing into the middle canopy and leaf yellowing and some leaf loss observed; mites scattered in the middle and top canopy [Economic threshold]

4 – lower leaf yellowing readily apparent and leaf drop common; stippling, webbing and mites common in the middle canopy; mites and minor stippling present in upper canopy [Economic injury]

5 – lower leaf loss common and yellowing moving to the middle canopy; stippling and distortion of upper leaves common; mites in upper canopy observed.

Organophosphates are the recommended insecticidal chemistry for twospotted spider mite control (e.g., dimethoate and chlorpyrifos). Most pyrethroids are not effective against twospotted mite except bifenthrin. Insecticides may not kill the eggs, thus a treated field should be scouted 7-10 days after application to determine if a second application is necessary. As always, refer to the label for the appropriate rates and re-entry intervals. To improve application coverage and contact of mites, consider increasing the water carrier volume. Treating field edges may be a cost effective option if heavy spider mite populations are restricted to edge rows.

Treatment of twospotted spider mites may not be required when temperatures drop below 85 degrees and humidity levels are greater than 90 percent for an extended time, because a naturally-occurring fungus can control populations. Mites that are infected by the fungus will appear brown, and will not move on the piece of paper used for scouting.

For more information, visit these websites:

Twospotted spider mites on soybean and corn (University of Minnesota)

Two-spotted spider mite management in soybean and corn (University of Wisconsin) 


Crops: CornMinor cropsSoybeanCategory: Crop ProductionInsects and MitesTags: pestmitesscoutingIPM