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Downwind Buffers and Susceptible Crop Restrictions for New Dicamba Products

Sat, 01/13/2018 - 09:26

In response to problems with off-target movement and injury associated with dicamba applications on dicamba-resistant (Xtend) soybean, the EPA made significant changes to labels of the new dicamba products.  While much of the discussion has focused on the Restricted Use designation and the requirement for applicators to receive dicamba-specific training, the EPA also clarified how downwind buffers and protections of susceptible crops are to be implemented.

Downwind buffers  The labels state that a 110 ft downwind buffer must always be maintained from the field edge (a 220 ft buffer is required if a rate greater than 22 oz of Xtendimax w/VGT or FeXapan w/VGT is used). There are four areas that can be included in the buffer distance when they are directly adjacent to the field:
1) roads, paved or gravel surfaces,
2) planted ag fields planted to crops tolerant to dicamba (e.g. grasses, Xtend soybean),
3) ag fields prepared for planting, and,
4) areas covered by buildings or structures with walls and or roof.

The implication of this restriction is that in most situations, a portion of the field will need to be left untreated due to the downwind buffer (Figure 1).  The EPA has clarified that the vegetation in the area between a field edge and a road is not considered part of the road; thus, if the wind is blowing toward a road, the buffer needs to be established in the field regardless of what is found in the field across the road.  It does not matter whether the roadside vegetation is maintained with mowing or other management practices.  

If permanent, perennial vegetation is present between two adjacent fields a downwind buffer will be required.  The label states that downwind buffers are required at field edges; thus, perennial vegetation found in terraces and waterways within fields do not require buffers.  

Figure 1.  Influence of wind direction on restrictions regarding downwind buffers and susceptible crops when using dicamba on dicamba-resistant soybean.

Susceptible crops  The labels state do not apply the product when wind is blowing towards adjacent susceptible crops.  Soybean varieties without the dicamba-resistance trait are considered a susceptible crop; thus, users of the new dicamba products will need to determine whether soybean planted in adjacent fields are dicamba-resistant or not.  The label does not specify a minimum distance required between treated fields and susceptible crops; however, a susceptible crop immediately across a road would be protected.  

The requirements for downwind buffers and protection of susceptible crops add to the complexity of using dicamba in dicamba-resistant soybean.  Users of the products need to carefully evaluate all fields prior to spraying season to determine where downwind buffers may be required and if susceptible crops are present in adjacent fields.  Restrictions for downwind buffers and susceptible crops are not affected by wind speed; thus, they are required even with low wind speeds.  The labels restrict applications to periods when winds are at least 3 MPH and less than 10 MPH.

The 2,4-D products registered for use on 2,4-D resistant corn and soybean (Enlist One and Enlist Duo) also have requirements for downwind buffers and susceptible crops.  However, the downwind buffer with the 2,4-D products are 30 ft rather than 110 ft specified for dicamba products.  The products can not be applied if the wind is blowing towards commercially grown tomatoes, grapes, cucurbits or other fruiting vegetables.  Soybean varieties that do not possess the 2,4-D resistant trait are not considered a susceptible crop.  At the time of publishing this article, Enlist soybean have not been approved for import by China.

Crop: SoybeanCategory: WeedsTags: dicambaherbicide driftherbicide applicationXtend soybeandicamba resistant soybean

New Dicamba Labels Issued

Wed, 01/10/2018 - 16:29

In October 2017, the Environmental Protection Agency reclassified Engenia®, FeXapan™ herbicide Plus VaporGrip® Technology, and Xtendimax® With VaporGrip® Technology as Restricted Use products and added additional restrictions and requirements to their use. One of the additional requirements stated that anyone wishing to apply these products must attend a dicamba or auxin-specific training. Recently, the Iowa Department of Agriculture and Land Stewardship issued Sec. 24(c) Special Local Need labels for Engenia®, FeXapan™ herbicide Plus VaporGrip® Technology, and Xtendimax® With VaporGrip® Technology. The 24(c) labels require all applicators that intend to apply these products to attend an Auxin Herbicide training that has been approved by the Iowa Department of Agriculture and Land Stewardship Pesticide Bureau and offered by a registered Auxin Herbicide training provider. The Agribusiness Association of Iowa is hosting a website, dicambatrainingiowa.org that will list the dates, times, and locations of programs that have been approved by the Iowa Department of Agriculture and Land Stewardship. The information listed will be updated as training programs are approved.This website also provides additional information related to the regulations of dicamba-based products for use with dicamba-resistant soybeans. Applicators must retain records that show they attended an IDALS approved auxin training prior to use of the product. Auxin training is not required prior to purchase or sale of Engenia®, FeXapan™ herbicide Plus VaporGrip® Technology, and Xtendimax® With VaporGrip® Technology in Iowa.

Crop: SoybeanCategory: Pesticide EducationTags: pesticide labelpesticide trainingdicamba resistant soybean

Summary of Soybean Aphid Efficacy Evaluation for 2017

Mon, 12/18/2017 - 08:35

2017 Statewide Summary

Spring planting conditions throughout Iowa were cold and wet, and most soybean fields were planted later to accommodate corn planting. June turned exceptionally dry, particularly in southern Iowa. Soybean aphids arrived on soybean in mid-June, as they normally do in northeastern Iowa. Hot and dry conditions in June favored twospotted spider mite colonization, particularly in southern counties. But as moisture stress subsided throughout Iowa, spider mite populations faded and soybean aphid colonization expanded. Some commercial fields experienced exponential growth of soybean aphid after bloom, especially in northern Iowa. In August, some fields in northwestern and northcentral counties had soybean aphid exceed the economic threshold. Some populations persisted until after seed set (R5–R6), but aphids quick crashed in most fields by mid-September. When insecticides were applied at full rates and had sufficient coverage, efficacy was good (i.e., >95% knockdown within three days after application) throughout most of Iowa. In some research trials near Sutherland, Iowa, poor knockdown with lambda-cyhalothrin was noted.

Project Description

Plots were established at two locations in 2017. Syngenta NK S24-K2 brand soybean was used at both locations. Seed did not have a pesticidal seed treatment unless specifically stated. At both locations, soybean aphid arrived in mid-June and populations peaked in early September. In the untreated control, aphid populations reached 132 per plant ± 39 (± SEM) at the ISU Northeast Research Farm on 12 September (Figure 1A), and reached 650 per plant ± 129 at the ISU Northwest Research Farm on 9 September (Figure 1B). The Northeast Research Farm did not reach the economic threshold, but the Northwest Research Farm did in mid-August. Plots were sprayed at both locations on 18 August. 


The cumulative aphid days for susceptible soybean treatments ranged from 648 to 14,004, and there were some significant differences among treatments (Figure 1A). The untreated control had significantly more CAD compared to all other treatments. Yield ranged from 55-62 bushels per acre with little significant difference among treatments (Figure 1B). Most of the CAD was accumulated in late August and early September, and did not affect yield among treatments.  

Figure 1A. Mean separation of cumulative aphid days + standard error of the mean treatments at the Northeast Research Farm in 2017. Means with a unique letter are significantly different at alpha = 0.10 (P<0.0001; F = 6.87; df = 18, 3).


Figure 1B. Mean separation of yield + standard error the mean for treatments at the Northeast Research Farm in 2017. Means with a unique letter are significantly different at alpha = 0.10 (P=0.1950; F = 1.34; df = 18, 3).


Management Recommendations

Population fluctuations between locations and years is typical soybean aphid dynamics for Iowa. My recommendation for soybean aphid management in Iowa is to:

  • Strongly consider using host plant resistance if soybean aphid populations are persistent and the seed agronomic traits are appropriate for the area. The use of a pyramided gene will result in lower CAD and reduce the need for foliar insecticides. 
  • Plant early if the field is in an area with persistent soybean aphid populations. 
  • Scout for soybean aphid, especially during R1–R5, and use a foliar insecticide if aphids exceed the economic threshold of 250 per plant. 
  • Use a product labeled for soybean aphid; most well-timed applications of foliar insecticides will provide yield protection if applied at the economic threshold and coverage is sufficient.
  • Evaluate foliar insecticide efficacy three days after application to ensure soybean aphid populations were sufficiently reduced.
  • Understand that late-season accumulation of CAD (i.e., after R5) may not impact yield like it does in early reproductive growth; a foliar insecticide applied after seed set may not be an economically profitable choice. 


Download the full summary of the 2017 efficacy evaluation for soybean aphid, through the ISU Extension Store.


Crop: SoybeanCategory: Crop ProductionInsects and MitesTags: SoybeanpestIPMaphidinsecticides

Crop Quality Management for Harvest 2017

Wed, 12/06/2017 - 08:39

Corn and soybean yields in 2017 were better than expected, which will add to the largest grain surpluses in recent years. As of the November 9, 2017 USDA crop production estimates, national corn yield estimates exceeded 2016 production and were closer to 2016 production in Iowa than preharvest expectations. Soybean yields are estimated to be lower than in the record year of 2016, but total US supply will be larger due to acreage increases.

CORN Yield (bu/a)   Production (billion bu.)         2016 2017 2016 2017 USA 174.6 175.4 15.14 14.58 IOWA 203.0 197.0 2.74


SOYBEAN Yield (bu/a)   Production (billion bu.)         2016 2017 2016 2017 USA 52.1 49.5 4.31 4.43 IOWA 60.5 56.0 0.57 0.56

As of September 1, 2017, there were an estimated 2.3 billion bushels of corn in storage (0.5 billion bushels in Iowa) and 301 million bushels of soybeans in storage (53 million bushels in Iowa).  Approximately 30% of the combined carryover was held on farms, and 70% in commercial facilities. By grain, 34% of corn and 29% of soybeans were held on farms.

The estimated grain storage balance (corn and soybeans, in billion bushels) for Iowa going into harvest in 2016 and 2017 was:

  2016 2017 Production 3.15 3.10* On Hand (9/01) 0.46 0.56 Total 3.61 3.68       Storage Capacity 2.90 3.00** Balance 0.71 0.68

*corn + soybeans
**USDA estimate, previous December

Gradual increase

This balance continued the gradual increase of grain on hand going into harvest. Approximately 700 million bushels, primarily corn, did not have a long term storage home, and therefore had to be placed in temporary storages, such as outdoor uncovered piles or plastic bags.  Iowa corn usage is 200-240 million bushels per month, which means the temporary storage should be emptied by January or February at the latest. US regions to the north and west that are converting small grain acres (such as wheat or barley) to corn have higher amounts of grain in outdoor storage than do Corn Belt states. The significance of the gradual growth in short term storage is that corn in these storages will use its shelf life faster than corn in well managed aerated and covered storage. Yet more and more of each years’ crop is being carried over, requiring storage times longer than a year. USDA is projecting an increase of 200 million bushels (to 2.49 billion bu.) in corn carryover at the end of the 2017 marketing year.


The 2017 growing season was characterized by significant swings in weather patterns, from very wet in the spring to very dry in June and July to moderate and wet in the latter part of the growing season. For a time, it appeared that the weather in the middle of season would both inhibit pollination and create moisture stresses for crop development. The US Drought Monitor reached the severe level in early August across much of the major growing area in the Western Corn Belt, and the extreme level in a four county area of South Central Iowa. Dry conditions peaked around August 5-10. The abrupt change of weather patterns in mid August, to moderate temperatures and wet, extended the growing season. This improved the fill and quality of both corn and soybeans. With extended growth, harvest moistures were higher and field drydown was slower than expected as of mid August. Grain quality was quite good; quality is normally determined by conditions at the end of the growing season.

Variety trials

We have been following public variety trials in selected Iowa locations for the past 9 years. 

Corn quality and yield data from widely corn hybrids in strip trials across Iowa.

Yields were near the highs of 2016, and test weights were excellent. Moisture was somewhat above average. Composition was good as indicated by above average protein content. Higher yields typically have reduced protein, density and test weight; that trend was not the case this year, likely because of favorable grain filling weather. Kernel filling, as measured by dry weight per kernel, was 5%-10% above normal, which accounts for the season-long underestimation of yields. Preharvest yield estimates use 5-year average weights per kernel.

Corn from the 2017 crop will be above the long-term average in feed value, and probably will have slightly lower ethanol yield per bushel. The high test weight will create good storability. It will be good corn to use for rotating the stock of 2016 crop that is still in storage.

Soybean quality and yield data from widely grown soybean varieties in strip trials across Iowa.

Yields were not as high as in the previous 3 years. The processing value, as measured by the total of protein and oil, was somewhat below average. Processors should be able to make soybean meal that is close to 47-48% protein, although meal quantities per bushel will be down. On a nationwide basis, we are seeing larger than normal variations in soybean protein and oil from north (lower) to south (higher). These will affect processor economics through meal and oil yields. Seed size is smaller that it would have been without the dry June and July. There was late growth of weeds, because rows did not fully cover in many cases. Expect foreign material levels to be higher than the normal 0.5 – 1.0%.


The high test weights and very good kernel fill should reduce grain storage problems. This is fortunate since long term storage is very likely with present surpluses.  The long run of low humidity conditions in late October, early November created low dewpoints and good grain cooling opportunities. Any grain in aerated storage should be at 35 F or below. Unaerated temporary (pile) storage is still at temperature risk depending on the grain temperature going into the pile. Piles filled from trucks as they came from the field will have more varying temperature and moisture conditions throughout the pile; aeration is the only way to even that out.

If grain is uniformly cool below 35F, it is not necessary to run fans steadily. In fact, excessive aeration creates weight shrink if the grain dries below the market standard moisture level (typically 15% for corn and 13% for soybeans). At today’s low prices and thin margins, losses from excess energy cost and unnecessary shrink can be significant. Removal by aeration of 1% extra moisture in corn will cost about four cents per bu in weight loss and about two cents per bu in energy cost. For soybeans, the cost would be about 12 cents per bu for the weight and two cents per bu for the energy.

The key to grain management is effective and consistent temperature monitoring. For bin sizes over 20,000 bu, this means some form of electronic temperature system. Manual monitoring is progressively less accurate as bin size goes up. An increase of three degrees F in two weeks, if the fans have not been run in the period, indicates spoilage somewhere in the bin.

Grain that is spoiling gives off carbon dioxide (CO2). Relatively inexpensive CO2 monitors can be used to track changes in CO2 levels, either at fan exhaust or in headspaces. Increase in CO2 (over a baseline established when the bin is filled) is actually a more sensitive indicator of spoilage than is a rise in temperature. Neither one will pinpoint the location of the trouble in the bin, although temperature sensing cables, common at elevators, will give more hotspot location information than will a general rise in CO2 levels.

The significant amount of carryover grain created situations where 2016 and 2017 grain could be mixed in the same bin. Mixing of old grain that has partially used its storage life with new grain that is not yet stable is likely to create storage problems. The best plan is to either rotate the new for the old, or combine lots of old crop so that the new crop can start an empty bin. Either of these creates extra work at harvest, but that work will pay back if the grain is stored into the next summer or longer. Any crop year mixtures should be the first grain out with fresh sales.

Finally, the shelf life of the grain (below) needs to be respected especially in conditions of long term storage. The storage time is progressively used at the various storage conditions through the year. If wet corn is held before drying, significant percentages of the storage time can be consumed, leaving less for the summer months. In 2016, for example, there were poor cooling conditions (high dewpoints). A lot of the storage life was used. There were many reports of spoilage from blue-eye mold in July and August 2017. In conditions of surplus with long term storage likely, do not waste the storage life in the fall; it cannot be recovered.

Crops: CornSoybeanCategory: Grain Handling and StorageTags: grain qualitygrain storage

Over 1,000 SCN-Resistant Soybean Varieties - All but 29 Have PI 88788 Resistance

Fri, 11/03/2017 - 08:31

The soybean cyst nematode (SCN) continues to be the most-damaging soybean pathogen in the US and Canada. The nematode is widespread in fields through Iowa and much of the Midwest. Management options for SCN include growing nonhost crops (such as corn), growing SCN-resistant soybean varieties, and using nematode-protectant seed treatments. Resistant soybean varieties have allowed farmers to produce profitable soybean yields in SCN-infested fields and keep SCN population densities relatively in check.

Many, many choices

The number of SCN-resistant soybean varieties available for Iowa soybean farmers has increased steadily since the early 1990s (see figure). Iowa State University publishes an updated list of SCN-resistant soybean varieties in maturity groups 0, 1, 2, and 3 annually to help farmers know their choices. Compilation of the list is supported by soybean checkoff funds from the Iowa Soybean Association.

The updated list (available online here) has just been released, and it contains 1,002 different named varieties, which is 46 more than last year and more than ever before. There are varieties from 35 companies. Many of the varieties have resistance to the herbicides dicamba, glufosinate, and/or glyphosate, and there are some with no herbicide resistance.

Very little diversity

Although there are more than 1,000 SCN-resistant varieties on the market, almost all of the varieties (97%) have resistance genes from the same breeding line or source of resistance, namely PI 88788 (see figure). Only 29 soybean varieties in the updated list have SCN resistance genes from sources other than PI 88788; these varieties are available from nine companies and Iowa State.

Figure: Number of SCN-resistant soybean varieties available for Iowa annually since 1991. The gray portion of each bar is the number of varieties with SCN resistance genes from PI 88788, the red portion is varieties with sources other than PI 88788.


Growing soybean varieties with the same SCN resistance genes each year is the same as repeatedly and consistently using a single pesticide active ingredient on a population of insects, fungi, or weeds. Eventually, the targeted pest population may develop resistance to the management tactic.

SCN populations with increased ability to reproduce on resistant varieties with PI 88788 resistance are now common in Iowa and in surrounding states. There have been fewer than 30 SCN-resistant soybean varieties available with resistance from a source other than PI 88788 for the last 12 years.

Managing SCN

Farmers should grow soybean varieties with different sources of resistance and also grow different soybean varieties of the common PI 88788 source of resistance to delay the build-up of resistance-breaking populations of SCN. Farmers also should have fields sampled to determine the levels of SCN present in the soil. A recent Iowa State Integrated Crop Management News article here has specific information on how to samples fields for SCN in the fall. More information about the biology and management of SCN is available at www.soybeancyst.info and www.soybeanresearchinfo.com/diseases/scn.html.

Crop: SoybeanCategory: Plant DiseasesTags: SCNSCN resistanceSCN management

Know Your SCN Numbers

Sat, 10/28/2017 - 12:40

Soybean farmers have kept the soybean cyst nematode (SCN) “in check” for decades simply by growing SCN-resistant soybean varieties. Unfortunately, prolonged use of varieties with SCN resistance genes from a breeding line called PI 88788 has resulted in SCN populations building up increased reproduction on resistant varieties. Almost all (97%) soybean varieties available to grow in Iowa have SCN resistance genes from PI 88788. This situation has led to dramatic and often unnoticed increases in SCN numbers in fields.

Need to know specifics

Now more than ever, farmers need to know if their fields are infested with SCN and what the numbers are. The higher the number of SCN eggs in the soil, the greater the yield loss - even with resistant soybean varieties

SCN is a consistent soybean yield reducer every year, not “hit or miss” depending on the weather as is the case with many pathogens and pests. The nematode survives very well in the soil, even through a few years of nonhost corn, and SCN will reduce yields every year that soybeans are grown in infested fields, regardless of weather.

Fall is a perfect time to sample for SCN

It is relatively easy to determine SCN numbers in fields. All it takes is collecting a soil sample to be tested for the nematode. And fall is a prime time to collect samples from fields in which soybeans will be grown in 2018.

Sampling guidelines:

  • It is best to use a soil probe, not a spade, to collect soil cores.
  • Collect soil cores to about 8 inches deep.
  • The more soil cores collected from the smaller the area, the more accurate the results will be. Collecting 15 to 20 soil cores from every 20 acres often is recommended.
  • Combine all soil cores in a bucket and mix well before placing the mixed soil into a soil sample bag.
  • Most private soil-testing labs in Iowa can process samples for SCN.
  • SCN samples also can be sent to Iowa State’s Plant and Insect Diagnostic Clinic, room 327 Bessey Hall, 2200 Osborn Drive, Iowa State University, Ames, IA 50011.

Example sampling pattern in a field with different management zones. Each “x” represents the location from which a soil core was collected.

Options for managing SCN

Managing SCN should involve coordinated use of multiple tactics. Management options include growing nonhost crops (such as corn), growing SCN-resistant soybean varieties, and using nematode-protectant seed treatments when soybeans are planted. Also, farmers should try to grow SCN-resistant soybean varieties with different sources of resistance and to rotate varieties within a resistance source to slow the development of resistance-busting SCN populations.

More information about SCN

More information about the biology and management of SCN is available at www.soybeancyst.info and www.soybeanresearchinfo.com/diseases/scn.html.

Crop: SoybeanCategory: Plant DiseasesTags: checking field for SCNfall samplingsampling for nematodesSCN

New Dicamba Labels Impact Application Timing

Wed, 10/25/2017 - 09:46

The EPA recently announced changes to the new dicamba labels in response to widespread off-target plant injury in 2016. The most significant change is classification of the new dicamba formulations as Restricted Use Products. Other changes will reduce the hours available to spray soybean, including 1) restricting applications to between sunrise and sunset, and 2) reducing the maximum wind speed during application from 15 mph to 10 mph. The ability to cover all acres in a timely manner has always been an issue and these new limits will add to that difficulty.

An earlier article described hours available to apply herbicides using restrictions on the first Xtendimax with Vapor Grip Technology label. In updating the article, box plots were used to display the distribution of available hours during two 7-day periods at different times in the growing season. Weather records for four different years were used, therefore providing 28 days in each analysis. Weather data from the ISU Research Farm near Boone was used.

The first bar plot of each time period shows hours with average wind speed between three and 10 mph during daylight hours (Figure 1). If there was a time frame where winds were within the allowed wind speeds for a single hour, that time was not included in the calculation. The second plot takes into consideration rainfall, subjectively determining how long the rain would keep a sprayer out of the field.

Wind speeds in Iowa are significantly higher in May than in June (Figure 1). When not considering rain, the average hours to spray was approximately five hours per day in late-May compared to nine hours in mid-June. In late-May, half of the days were totally lost for spraying based on wind and rain restrictions. As with wind, rain was a bigger factor in limiting spray hours in May than in June.


While the analysis was conducted with the new dicamba labels in mind, the graphs clearly show the pressure applicators are under to complete timely spraying of fields, regardless of herbicide. This is one of the many benefits of preemergence herbicides, spreading out the window for postemergence applications. While applications later in the season provide more hours to complete spraying, temperatures are higher, increasing the risk of volatilization of dicamba.

This page provides a simple explanation of box plots.

Crop: SoybeanCategory: WeedsTags: dicambawind speedherbicide application

Sampling for Nematodes that Feed on Corn Not Advised in the Fall

Sat, 10/21/2017 - 13:12

Lately there have been lots of questions asked about sampling fields for plant-parasitic nematodes that feed on corn. This diverse group of microscopic worms includes some species that cause yield loss at very low population densities (numbers), other species that are not harmful until population densities reach many hundreds or more per 100 cm3 (a little less than a half-cup) of soil, and still other species that are not thought to be harmful to corn at all.

It is common for Iowa fields to have several species of plant-parasitic nematodes present at low numbers. It’s only when numbers reach damaging levels that symptoms of injury will appear.

Unfortunately, fields cannot be sampled in the fall to assess the situation. Sampling to check for damaging levels of nematodes needs to be done during the growing season - ideally when symptoms of damage are seen. Following are guidelines on how to collect samples for assessing the potential for damage and yield loss caused by nematodes that feed on corn.

What type of sample should be collected?

Up until V6 growth stage of corn - collect soil and root samples

  • Use a soil probe and collect cores that are at least 12 inches long.
  • Collect 20 or more soil cores to represent an area.
  • Collect soil cores from within the root zone of plants showing symptoms of damage.Combine (but do not mix) the soil cores and place them in a sealed plastic bag labeled with permanent marker.
  • Also collect, with a shovel, the root mass from 4 to 6 plants with symptoms of damage (see Figure). Take care not to strip off the smaller, seminal roots. The tops of the plants can be cut off and discarded. Place the roots in a sealed plastic bag labeled with permanent marker.
  • Protect the samples from physical jarring and keep the samples cool (room temperature or below).

Figure: Young corn plant collected to test for plant-parasitic nematodes in root tissue.









From V6 through R3 (milk) corn growth stage - collect soil samples

  • Use a soil probe and collect cores that are at least 12 inches long.
  • Collect 20 or more soil cores to represent an area.
  • Collect soil cores from within the root zone of plants showing symptoms of damage. Combine (but do not mix) the soil cores and place them in a sealed plastic bag labeled with permanent marker.
  • Protect the samples from physical jarring and keep the samples cool (room temperature or below).

From R4 (dough) corn growth stage to harvest - sampling is not recommended

There is not a reliable relationship between damage or yield loss and the number of nematodes present in soil and roots once the corn crop reaches the R4 growth stage. Therefore, sampling is not recommended after this point in the growing season.

Where to send samples?

Several private laboratories and most land-grant university plant diagnostic laboratories or clinics process samples and determine the identities and numbers of plant-parasitic nematodes present. A list of the university laboratories and their contact information can be found online.

At Iowa State University, the facility's location and address are: Plant and Insect Diagnostic Clinic, Room 327 Bessey Hall, 2200 Osborn Drive, Iowa State University, Ames, IA 50011.

The test for nematodes that feed on corn from the ISU Plant and Insect Diagnostic Clinic is called the complete nematode count. Samples sent to the ISU Clinic should be accompanied by a Nematode Sample Submission Form (ISU Extension Publication "PIDC 32").

Management options if damaging levels of nematodes are found

If damaging population densities of nematodes are found, there is nothing that can be done during the season to manage the nematodes and lessen the yield loss. Management options for future corn crops include use of soil-applied Counter® 20G nematicide and/or seed treatments such as Avicta®, Votivo®, and Nemastrike™. Use of these management options must be decided upon before the corn crop is planted.

Crop: CornCategory: Plant DiseasesTags: nematodessampling for nematodes

A Guide to Choosing Corn Hybrids

Mon, 10/09/2017 - 10:21

When you think about which hybrids to plant next season, make sure to take into account all the relevant factors. When selecting hybrids, prioritize yield potential and risk management. There are a number of other components to consider as well, including transgenic options, disease tolerance, maturity, grain dry down, standability, stalk quality, and early season vigor ratings.

Choose a diverse mix of hybrids to reduce the risk associated with the weaknesses of any individual hybrid. Four to five different hybrids are recommended for most farms, but larger farms may consider even more. Obtain diversity by choosing high-yielding hybrids that differ in relative maturity, disease resistance, insect resistance, or other traits. Planting multiple hybrids can also spread out the maturity dates, which will spread out the timing of pollination and other key stages as well as your workload.

Yield and yield consistency

Genetic diversity is important, but yield is the most important factor to consider when choosing hybrids. The best production strategies will not result in high yields if you don’t choose high-yielding hybrids. Reevaluate the hybrids you choose every year. Newer hybrids typically offer higher yield potential than those that have been on the market for several years. 

Look for hybrids that have consistently high yield performance from location to location and from year to year. To ensure this, look at multiple data sources, including public hybrid trials such as those conducted by the Iowa Crop Improvement Association as well as seed company and retailer trials. University trials are helpful because they can compare the yield potential of hybrids from multiple brands in a more rigorous plot design compared to hybrid strip trials. Also look at your own performance trials, as well as strip trials from other farmers, FFA clubs, and cooperatives. Use as much data as you can to ensure a reliably good hybrid choice.

Transgenic options

A number of transgenic options are available to Iowa farmers and they may be appropriate choices for your farm. Many hybrids have traits for insect protection and most have herbicide traits. Think about whether you need all of the traits or will use the traits that are available in a given hybrid and evaluate whether transgenic hybrids would be more beneficial to your crop compared to conventional hybrids. Transgenic hybrids have been very successful where insect resistance and herbicide resistance has not become an issue. Consider what genetic traits are useful and effective in your fields. 

Other risk management factors to consider

Another part of your decision-making process should be disease tolerance. One way to prevent disease could be choosing a hybrid that has resistance or tolerance to diseases typical of your production environment. Look for disease ratings to minimize risk of disease pathogen infections. Consider whether hybrid disease ratings can be used to offset the need of in-season foliar fungicide applications. 

Grain dry down is an important factor, especially for farmers who have limited or no drying facilities on their farms. When you look for hybrid dry down characteristics, you should also consider hybrid maturity. Earlier maturing hybrids have a greater potential for field dry down while later maturing hybrids have less field dry down potential and greater risk of a killing fall frost. Be careful when choosing a hybrid for this reason. Both maturity selection and dry down characteristics can be exploited to achieve similar goals.

Standability and stalk quality are characteristics to consider to ensure production is harvestable. While hybrids are often characterized for standability and stalk quality, weather conditions throughout the growing season can have a large influence. You can help evaluate the performance of hybrids in this area by doing a pinch test on corn stalks in all your fields every year. This will provide some data with which to evaluate your hybrid’s performance on your farm for the given management and weather conditions.

Early season vigor is key to a strong season and getting adequate stand establishment. With hybrid selection occurring well ahead of planting, hybrids with good early season vigor can help protect against unpredictable weather conditions in April and May. Considering seedling vigor is especially important if you plant cover crops, plant into high residue situations, or have soils that are typically cold and wet in the spring.

Choosing diversity

Crop rotation and management practices can and should influence the hybrids that get selected for an individual field. The previous year’s hybrid genetics do not have an influence on the current year’s hybrid performance. However, planting hybrids with the same insect/herbicide traits for multiple years puts you at a greater risk of resistance development. It is also known that hybrids can respond differently to the farming practices being used. Select hybrids that match your management. For instance, if the field is in continuous corn, rotate transgenic traits used for insect protection and select a hybrid that is best suited for continuous corn.

While understanding that corn hybrids should be placed according to management practices being used, also realize the hybrid selection can be an integral part of a pest management program. Transgenic traits and disease ratings can be used to determine if in-season foliar fungicides are needed and dictate aspects of the herbicide program being used.

Seed costs

Seed cost is an important factor when choosing your hybrids. Seed discounts are offered for quantity and early payment. These are great opportunities that should be taken into consideration. Weigh the benefits of your hybrids (insect-repellant, disease-resistant, etc.) against tradeoffs in your herbicide and fungicide programs. Balancing the level of transgenic traits attained versus the cost for alternative management can provide an opportunity to save seed costs with additional expense for pesticides. These tradeoffs should be considered when considering conventional or various levels of trait inclusion.

In summary, prioritize yield potential and risk management when choosing hybrids. Choose a diverse mix of hybrids. Consider the transgenic hybrids that may fit your farm situation. Evaluate hybrids based on their disease resistance, their potential for dry down and maturation, their standability, and their early season vigor. Plant new hybrids frequently to prevent resistance development. Make sure to keep cost in mind by balancing hybrid benefits with their price tag to ensure that you make profitable decisions.

Crop: CornCategory: Crop ProductionTags: hybrid selectioncorn maturitycorn management

What to Look For in Choosing Soybean Varieties

Tue, 10/03/2017 - 08:13

When looking for soybean varieties, it is important to give as much thought to the process as you give to choosing corn hybrids. If you only choose one or two soybean varieties and do not take into consideration management and environmental factors of your operation, you are likely limiting yield potential.

Many of the factors that apply to choosing corn hybrids apply to soybean variety selection as well. Choose high-yielding soybean varieties. You cannot achieve high yields from low-yielding genetics. Look for varieties that perform well from field to field and year to year. Take into account your unique management and environmental situation by choosing varieties that are well suited for your management practices and field conditions. When weighing these factors, use all the data you can find to make your decision. Look at performance trials done by a university, your own performance trials, seed company reports, as well as strip trial results from other farmers, FFA clubs, and cooperatives.

Maturity selection

Maturity selection is another thing to keep in mind when you choose soybean varieties. You can minimize the effects of adverse weather and expand the harvest window by planting varieties with different maturities. Keep in mind that generally speaking, later maturing soybeans have higher yields. It can be a challenge to compare maturities among seed companies. Actual maturities may vary and are highly influenced by environmental factors. It is recommended to plant varieties with a range of 0.5 to 1.0 maturity group.

Disease and herbicide traits

Transgenic options in soybean varieties are limited to the various herbicide traits. Choose the herbicide traits and technologies that make sense to achieve control of your weed populations. Plant breeding efforts have resulted in the development of soybean varieties with resistance or tolerance to soybean cyst nematodes (SCN), sudden death syndrome (SDS), brown stem rot, iron deficiency chlorosis (IDC), white mold, and phytopthora.

In Iowa, the most important trait to look for is resistance to SCN, since SCN can reduce soybean yield by up to 30%. SCN is known to interact with SDS and IDC. Because of this, managing SCN is extremely beneficial in the presence of SDS and IDC. Management of SDS and IDC can be particularly effective when using genetic selection to minimize impacts in the field. However, newer pesticide technology is also available for SDS control. Soybean varieties are often rated on phytophthora and white mold resistance. Identifying varieties with resistance or tolerance to these diseases should be considered. However, don’t sacrifice high yielding genetics. All these factors need to be balanced with what can be managed by genetic selection or other available control measures.

Standability and shattering

Standability and shattering should also be considered. Soybeans planted at higher seeding rates or in fields with high fertility are more susceptible to lodging due to taller plant growth. If lodging becomes a significant factor in your fields, it could reduce yield and slow harvest progress. Pod shattering is typically associated with harvest delays where seed moisture falls below 13% and then goes through rehydration and drying cycles. Shattering can be minimized by paying attention to variety scores as well as selecting a range of soybean maturity groups.

Finally, as you consider all these factors, don’t forget to keep seed cost in mind. The highest-yielding variety may not be the most profitable. Seed cost must be balanced with yield potential as well as other management costs. Using genetics to manage weeds, insects, and diseases may provide a greater return on investment than relying on pesticides, or at least it will provide an alternative for risk management.

Crop: SoybeanCategory: Crop ProductionTags: variety selectionmaturityyield potential

Fall marestail (horseweed) management

Mon, 10/02/2017 - 09:06

Marestail (Conyza canadensis) is one of the most difficult weeds to manage in no-till soybean.  While classified as a winter annual, the plant has significant emergence in both late summer/early fall and in the spring.  This extended emergence period greatly complicates management since the success of postemergence product is closely tied to plant size.  Attempting to control populations at the time of planting often results in control failures as fall-emerged plants are too large for acceptable control.

Fall-emerged plants can be effectively controlled with fall or early-spring herbicide applications; however, weather conditions frequently interfere with early spring applications.  This allows marestail that emerged in the fall to get too large for consistent control.  For this reason, fall applications are a more consistent strategy.  Glyphosate-resistant marestail is widespread across Iowa, thus 1 lb a.e. 2,4-D per acre is recommended as the base treatment for marestail burndown treatments.  Glyphosate or other products may be tank-mixed with 2,4-D to provide broader spectrum control of winter annuals and certain perennial weeds.  We generally do not recommend including residual herbicides in fall applications since they provide little benefit in managing weeds that emerge the following spring.  A bulletin developed by the Take Action on Weeds group, sponsored by the United Soybean Board, provides more detailed information on marestail management.

Most areas of the state received sufficient rain during September to promote germination of winter annuals.  However, the only way to determine the benefit of fall herbicide applications for marestail is to scout fields prior to or after harvest.  A no-till field near Ames had two distinct sizes of marestail on October 1 (Figure 1).  The larger seedlings probably emerged following mid-August rains, whereas the smaller ones likely emerged following rains on September 16-18.  Applications can be made into November, but target applications for when high temperatures are at least in the mid-50’s. 

Figure 1.  Abundant marestail present in a no-till field on Oct.1, prior to soybean harvest.

Remember, fall applications are unlikely to eliminate the need for burndown treatments at planting.  Marestail and other weeds adapted to cool temperatures (e.g. lambsquarters, giant ragweed) are likely to emerge prior to planting, making it necessary to control these weeds to provide the crop an even start with weeds.  Rye cover crops are effective at suppressing establishment marestail and other winter annuals, and should be considered in future years.

Crop: SoybeanCategory: WeedsTags: horseweedmarestailConyza24-Dfall applications