Herbicide Residue Considerations for Fall Cover Crop Establishment

Source: Alyssa Essman, Mark Loux, OSU

Herbicides with residual that are used in corn and soybeans can affect the establishment of fall-planted cover crops, and should be taken into account when planning cover crop practices and selecting species. Soil characteristics and weather also play a role in the persistence of residual herbicides, which can vary by field and year. More information is needed on rotational intervals for many cover crop species, and this information is often not included on herbicide labels. University weed scientists have studied the effect of residual herbicides on some of the most popular cover crop species in order to provide this information to growers. In general, residual herbicides that control grass weeds can hinder establishment of grass cover crop species. Broadleaf cover crop species are most impacted by group 2 (ALS inhibitors), 5 (PSII inhibitors), 14 (PPO inhibitors), and 27 (HPPD inhibitors) herbicides (Purdue University).

A multi-state study found that the general order of sensitivity of cover crops to herbicide carryover, from greatest to least sensitive, is:

  • Tillage radish > Austrian winter pea > crimson clover = annual ryegrass > winter wheat = winter oats > hairy vetch = cereal rye.

Soybean herbicides that tended to be most injurious were:

  • Fomesafen, pyroxasulfone, imazethapyr, acetochlor, and sulfentrazone.

Corn herbicide treatments that were most injurious to cover crops were:

  • Topramezone, mesotrione, clopyralid, isoxaflutole, pyroxasulfone, and nicosulfuron

(University of Missouri).

Below is a table of commonly used corn and soybean herbicides, the fall cover crops that are safe to plant in rotation, and cover crop species that may be injured following these herbicides (Adapted from Lingenfelter D. and Curran W., Penn State University).

 

 

Cover crops provide a multitude of benefits and their use is becoming an increasingly popular practice in Ohio. Including cover crops in rotation with agronomic crops to realize these benefits costs time and money. It is important to evaluate the potential risk of herbicide residue on the establishment of cover crops in order to ensure success. Residual herbicides applied at the time of planting typically interfere with cover crop establishment less than those applied POST. Weather can affect the persistence of herbicides also, especially rainfall in summer.  The risk of residual herbicides affecting cover establishment will be higher in areas that have been dry since herbicide application.  Risk will be lower where the herbicide application was followed by some wet weather to get herbicide degradation started, compared with an application during prolonged dry weather.  One of the least problematic cover crop species is cereal rye, which can be successfully established following a late corn or soybean harvest, and is tolerant to a most of the most commonly used corn and soybean herbicides. Weed control should continue to be the priority in selecting herbicides, and cover crop species selection should be based on potential injury and goals for the use of cover crops.  The introductory section of the “Weed Control Guide for Ohio, Indiana, and Illinois” has some of the same information presented here, and OSU weed scientists also summarize this in a video: https://www.youtube.com/watch?v=ylr0zGnXMfs

The following resources contain information on residual herbicides and cove crops also:

https://extension.psu.edu/corn-herbicides-and-rotation-to-cover-crops https://extension.psu.edu/soybean-herbicides-and-rotation-to-cover-crops

https://ipm.missouri.edu/IPCM/2020/3/coverCropTermination-KB/

https://ag.purdue.edu/btny/weedscience/Documents/covercropcarryover.pdf

Preharvest Herbicide Treatments

Source:  Mark Loux, OSU

Information on preharvest herbicide treatments for field corn and soybeans can be found in the “Weed Control Guide for Ohio, Indiana, and Illinois”, at the end of these crop sections (pages 72 and 143 of the 2020 edition).  Products listed for corn include Aim, glyphosate, and paraquat, and for soybeans include Aim, paraquat, glyphosate, and Sharpen.  Some dicamba products are also approved for preharvest use in soybeans, and some 2,4-D products are approved for use in corn, and these are not listed in the guide.  The basic information for these follows:

Dicamba – soybeans:  Apply 8 – 32 oz/A (4 lb/gal products) as a broadcast or spot treatment after soybean pods have reached mature brown color and at least 75% leaf drop has occurred; soybeans may be harvested 14 days or more after a pre-harvest application; do not use preharvest-treated soybean for seed unless a germination test is performed on the seed with an acceptable result of 95% germination or better; do not feed soybean fodder or hay following a preharvest application of this product.

2,4-D – corn:  Labels vary with regard to types of corn that can be treated (some indicate no sweet corn) and based on whether crop is being grown for seed.  Apply after the hard dough (or dent) stage when silks have turned brown.  Weed seed production can be suppressed if applied prior to the flowering stage.  Allow 14 days between application and grain harvest.  Do not forage or feed corn fodder for 7 days after application.

Preharvest herbicide treatments are primarily intended to suppress/kill and dessicate weeds that can make harvest more difficult.  Products with contact activity will cause faster dessication and leaf drop of weeds, but may be less effective at killing weeds compared with systemic products.  Effective dessication with contact herbicides may still require a wait of a week or more following application, and this can can vary by weed.  The maximum paraquat rate is well below the rate required to actually kill large weeds, but it is still probably most effective for dessication of morninglory.  Glyphosate is not likely to be effective on marestail and waterhemp, and many giant ragweed populations, whereas dicamba or 2,4-D may with enough time between application and harvest.  The first frost will usually provide results similar to herbicides, so in a situation where crop maturity is delayed or the infested field can be harvested later in fall, consider whether a herbicide treatment is actually needed.  Preharvest treatments can also be effective for control of warm season perennials, and the systemic herbicides will be most effective where this is the goal.  Keep in mind also that for weeds with fruits that can contaminate harvest, such as black nightshade, the preharvest treatment can dessicate the foliage but will not affect the fruits, except that dessication of weeds may result in fruits closer to the soil.

Preharvest treatments are not intended to be used to speed up crop maturity, and largely do not accomplish this.  The restrictions on preharvest treatments that specify how mature the crop must be at time of application are designed to minimize any effect of herbicides on crop maturation.  Applying earlier than specified could interfere with that process.  The residue tolerances for this use are also based on a certain application timing, and failure to follow label guidelines could result in illegal herbicide residues in grain.  For crops being grown for seed, and for sweet corn and popcorn, be sure to check with the seed company/processor for approval prior to using any preharvest treatments.

Changes in status of dicamba product labels for Xtend soybeans – a recap

DSource: Dr. Mark Loux, OSU

 

Ohio Department of Agriculture: Dicamba use in Ohio ends June 30, 2020

 

On June 3, the US 9th Circuit Court of Appeals issued a decision in a case concerning the use of dicamba on Xtend soybeans.  This decision voided the labels for XtendiMax, Engenia, and FeXapan that allows use on Xtend soybeans.  Tavium was not included in this decision, because it was not approved for use when the case was initially filed.  Several excellent articles covering this decision can be found here on the OSU Ag Law blog (https://farmoffice.osu.edu/blog).  EPA stated on June 8, providing further guidance about what this decision means for the use of dicamba for the rest of this season.  The gist of this decision was the following:

“EPA’s order addresses sale, distribution, and use of existing stocks of the three affected dicamba products – XtendiMax with vapor grip technology, Engenia, and FeXapan.

  1. Distribution or sale by any person is generally prohibited except for ensuring proper disposal or return to the registrant.
  2. Growers and commercial applicators may use existing stocks that were in their possession on June 3, 2020, the effective date of the Court decision. Such use must be consistent with the product’s previously-approved label, and may not continue after July 31, 2020.”

ODA subsequently issued a statement regarding the registration and use of these products in Ohio, stating that any application must happen before July 1, 2020.  Partial text from this statement:

“The registration of these products (XtendiMax, FeXapan, and Engenia) in Ohio expires on June 30, 2020. After careful evaluation of the court’s ruling, US EPA’s Final Cancellation Order, and the Ohio Revised Code and Administrative Code, as of July 1, 2020, these products will no longer be registered or available for use in Ohio unless otherwise ordered by the courts.

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True Armyworm Infestations

Source: Andy Michel, Curtis Young, CCA, Kelley Tilmon, OSU

 

As you scout your fields this week be on the lookout for this pest!

 

We received many reports of true armyworm infestations in wheat, barley, and corn. These are black or green caterpillars with stripes along the side and orange heads.  In the spring, true armyworm moths migrate from the south and lay eggs in grasses such as forage and weed grasses, winter wheat and barley, and rye cover crops.  When the eggs hatch, the larvae can significantly damage wheat and barley before then moving to young corn. Usually, moth flights occur in April, but we may have had a second peak the first or second week of May—it’s likely the caterpillars feeding now are from this later flight. Right now, wheat, barley, and corn should be inspected for true armyworm populations. Armyworms like to hide during the day and feed at night, so scouting should occur at dusk or dawn, and/or on cloudy days.

Corn: True armyworm in corn cause the most damage when planted in no-till grassy fields, such as a rye cover crop.  In this case, after feeding on the cover crop, the caterpillars shift onto the emerging corn.  The name armyworm comes from the caterpillars’ behavior of migrating en masse from one location to another. Thus, one should pay particular attention to cornfields adjacent to wheat fields that may have supported a high armyworm population, especially the first several rows into the cornfield. As the wheat matures and dries down, it could stimulate the caterpillars to move.

One may only need to treat the edge of the field closest to the wheat field from which the caterpillars are marching. If armyworms are found in a cornfield, check for the percentage of plants damaged in 5 sets of 20 plants.  If more than 10% of the stand has feeding damage, it may indicate a large infestation, and the field should be re-checked in a few days to see if defoliation is increasing. If defoliation has increased and plants have two or more caterpillars per corn seedling, an insecticide application may be necessary. However, if most larvae are longer than 1 inch, then much of the feeding is complete as the caterpillars will begin to pupate. Also, look for the presence of diseased (black and shriveled) or parasitized caterpillars (having a few or several small, white egg cases on their body)—if found, do not include them in your counting.

If defoliation exceeds 50%, even a rescue treatment may not recover the field without a significant impact on yield.  According to the Handy Bt Trait Table (https://agrilife.org/lubbock/files/2020/02/BtTraitTable_FEB_2020.pdf), only the Vip3A (e.g., Viptera) Bt trait is effective against true armyworm.  Insecticidal seed treatments may offer some control but can be overwhelmed with high populations. Plus, insecticidal seed treatments last only about 4-6 weeks after planting.

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ODA Statement on Dicamba – Official Statement Regarding the Use of Over-the-Top Dicamba Products

Source: C.O.R.N. Newsletter

Official Statement Regarding the Use of Over-the-Top Dicamba Products

 

 

On June 3, 2020, the U.S. Court of Appeals for the Ninth Circuit rendered a decision which vacated the federal registrations of three of the four dicamba products that had previously been approved for use on dicamba-tolerant (DT) soybeans. This decision has caused tremendous uncertainty for soybean producers and pesticide dealers during an agronomically critical time of year.  It is estimated that around 40 to 50 percent of the soybean crop planted in Ohio are dicamba tolerant varieties. The specific products impacted are:  XtendiMax with VaporGrip Technology, Engenia Herbicide, and DuPont FeXapan with VaporGrip Technology. Tavium plus VaporGrip Technology for use on DT soybeans was not covered by this ruling.

In response to the decision, on June 8, 2020, the United States Environmental Protection Agency (US EPA) issued a Final Cancellation Order that outlines specific circumstances under which existing stocks of the three affected dicamba products can be used. The registration of these products in Ohio expires on June 30, 2020.  After careful evaluation of the court’s ruling, US EPA’s Final Cancellation Order, and the Ohio Revised Code and Administrative Code, as of July 1, 2020 these products will no longer be registered or available for use in Ohio unless otherwise ordered by the courts.

While use of already purchased product is permitted in Ohio until June 30, 2020, the Court’s decision and US EPA’s order makes further distribution or sale illegal, except for ensuring proper disposal or return to the registrant. Application of existing stocks inconsistent with the previously approved labeling accompanying the product is prohibited.  If you have questions about returning unused products, please reach out to your pesticide dealer’s representative.

For additional questions, please email pesticides@agri.ohio.gov or call 614-728-6394, and visit ODA’s website for updates.

Dicamba takes another blow: Court of Appeals vacates dicamba registration

Source: Peggy Hall, OSU Extension

Dicamba has had its share of legal challenges, and a decision issued yesterday dealt yet another blow when the Ninth Circuit Court of Appeals  vacated the product’s registration with the U.S. EPA.  In doing so, the court held that the EPA’s approval of the registration violated the provisions of the Federal Insecticide, Fungicide, and Rodenticide Act (“FIFRA”), which regulates the use of herbicides and other chemicals in the U.S.  Here’s a summary of how the court reached its decision and a few thoughts on the uncertainty that follows the opinion.

What now?

The court raised the issue we’re all wondering about now:  can growers still use the dicamba products they’ve purchased?  Unfortunately, we don’t have an immediate answer to the question, because it depends largely upon how the EPA responds to the ruling.  We do know that:

  • FIFRA § 136a prohibits a person from distributing or selling any pesticide that is not registered.
  • FIFRA § 136d allows the EPA to permit continued sale and use of existing stocks of a pesticide whose registration is suspended or canceled.  The EPA utilized this authority in 2015 after the Ninth Circuit Court of Appeals vacated  the EPA’s registration of sulfoxaflor after determining that the registration was not supported by substantial evidence.  In that case, the EPA allowed continued use of the existing stocks of sulfoxaflor held by end-users provided that the users followed label restrictions.  Whether the agency would find similarly in regards to existing stocks of dicamba is somewhat unlikely given the court’s opinion, but remains to be seen.  The EPA’s 2015 sulfoxaflor cancellation order is here.
  • While the U.S. EPA registers pesticides for use and sale in the U.S., the product must also be registered within a state in order to be sold and used within the state.  The Ohio Department of Agriculture oversees pesticide registrations within Ohio, and also regulates the use of registered pesticides.
  • If the EPA appeals the Ninth Circuit’s decision to the U.S. Supreme Court, the agency would likely include a request for a “stay” that would delay enforcement of the court’s Order.
  • Bayer strongly disagrees with the decision but has paused its sale, distribution and use of XtendiMax while assessing its next step and awaiting EPA direction.  The company states that it will “work quickly to minimize any impact on our customers this season.”  Bayer also notes that it is already working to obtain a new registration for XtendiMax for the 2021 season and beyond, and hopes to obtain the registration by this fall.  See Bayer’s information here.
  • BASF also states that it is awaiting the EPA’s reaction to the decision, and that the company will “use all legal remedies available to challenge this Order.”
  • Corteva is also reviewing its options and has clarified that its Tavium Plus VaporGrip dicamba-based herbicide is not part of the ruling.

Click here to read the entire article.

Burndown and Residual Herbicide Issues

 

Source:  Mark Loux, OSU

Depending upon where you are in the state, it’s possible right now to be experiencing delays in getting anything done, progress in planting but delays in herbicide application, weather too dry to activate residual herbicides, and/or reduced burndown herbicide effectiveness on big weeds due to cold weather.  What’s become a typical Ohio spring.  Some information relative to questions that OSU Extension educators have passed on to us:

1.  Residual herbicides and rainfall.  Residual herbicides do vary in the relative amounts of rain needed for “activation”, or adequate movement into the soil to reach germinating seeds.  Most growers are applying mixtures or premixes of several products, so we’re not sure these differences are as important as the overriding principle here.  Residual herbicide treatments need to receive a half to one inch of rain within a week or so after tillage or an effective burndown treatment, to control weeds that can will start to emerge at that time.  This varies with timing of application and weather.  Summer annual weeds are the target here, and their emergence ramps up in early May, although cold weather can slow this down.  So residual herbicides applied in mid-April, prior to most of the summer annual weed emergence, may not need rain as soon after application, compared with herbicides applied in May.  Aside from this, residual herbicide activity is not really dependent upon soil reaching a certain temperature.  Under more marginal rainfall conditions, it’s possible that herbicides may control the small-seeded weeds that emerge at or just below the soil surface, but be less effective on larger-seeded weeds that can emerge from deeper.  In a tilled situation, a timely rotary hoe can be used to remove some of the weeds that are about to emerge (the “white stage”) and buy some time for rain.  The good news here is that we have effective POST herbicides to remedy many situations where the residual herbicides are not completely effective.

2.  Residual herbicides and crop injury. The concerns here seem to be more about soybean herbicides, which may partly reflect the overall greater safety of residual corn herbicides.  Several residual soybean herbicides can cause injury, depending upon when they are applied relative to planting, rainfall, soil type, seeding depth, etc.  These include products that contain metribuzin, sulfentrazone, flumioxazin, and chlorimuron.  One of the things that has reduced our risk of injury from all of these herbicides is that in no-till soybeans they have usually been applied a week or more prior to planting to accommodate restrictions on 2,4-D ester and dicamba.  Application at or after planting increases the risk of injury, as does use in tilled situations.  We have increased metribuzin use substantially over the past decade, but injury has been extremely rare due to application prior to planting and use of relatively low rates in combination with other products.  We hear more about injury or suspected injury from flumioxazin and sulfentrazone when wet weather delays planting and forces application of residual herbicides after planting.  It’s worth noting here also that the Xtend and Enlist soybean systems do away with the wait to plant soybeans for dicamba and 2,4-D, respectively, and more growers may be waiting until after planting to apply burndown/residual herbicides.

In brief, symptoms of these are as follows:  chlorimuron – slowed development, stunting, yellowing; flumioxazin and sulfentrazone – necrosis on young leaves and stem, stunting; metribuzin – usually delayed until first trifoliate, yellowing and possibly necrosis on margins of older leaves.  Cloransulam, imazethapyr, and imazaquin are generally safer on soybeans than chlorimuron, in situations where injury is a concern.  Activity of metribuzin varies considerably with soil texture and organic matter content, so using the labeled rate for soil type is important.  Injury from any of these may be more likely when herbicide application is delayed for several days after planting, followed by substantial rain as the soybeans are about to emerge.  Labels for products containing flumioxazin state that soybeans should be planted 1 ½ inches deep and herbicide should be applied no later than three days after planting, in an attempt to avoid this situation (does not always work).  The good news here is that early injury to soybeans usually does not reduce stand, but may slow early growth and rate of crop canopy development and leave soybeans open to the effect of other stresses.  In some of these situations, it can be difficult to sort out how much of the damage is due to herbicide and how much is due to other factors.  Yield loss is probably infrequent based on the soybean plant’s ability to compensate for these types of factors.

3. Cold weather and burndown herbicides.  We had a fairly warm winter and early spring, followed by the recent month of colder than normal weather.  The net result of this is large winter annual weeds, and weather that is currently not terribly conducive for burndown activity.  There is not much specific guidance on herbicide labels about cold weather, just general statements about how effectiveness can be reduced under adverse conditions that include cold weather.  We expect many experienced applicators may have their own set of rough guidelines on this, or at least gut feelings.  Under cold conditions, the rate of herbicide activity declines and also the overall effectiveness.  It’s more difficult to define the weather conditions when herbicide should not be applied.  These would certainly include periods when frost or freeze is occurring overnight and daytime weather is cool and cloudy (less than about 50).  One night of frost followed by a warm sunny day may still allow for decent herbicide activity, if weeds appear sufficiently recovered from the frost.  Aside from this we could make a general recommendation to keep applying as long as night and day temperatures are at least 40 and 60 to 70, respectively, although this is still not ideal compared with day temperatures higher than 70 with sun.  One way of dealing with this problem is to just wait for a return to warm, sunny weather before applying burndown herbicides.  Another is to increase herbicide rates and use a more comprehensive herbicide mixture.  For example, adding Sharpen to a mixture of glyphosate plus 2,4-D or dicamba.  As with the less than effective residual herbicides under dry weather, burndown herbicide problems can sometimes be resolved with an effective POST treatment of glyphosate, 2,4-D, or dicamba, depending upon the trait system.

4. Reminder about the value of fall herbicides.  Fall herbicides are an essential tool for marestail management, but given our current situation of dense, big weeds in no-till fields and potential problems with burndown herbicide effectiveness, it’s worth reminding all of us why fall herbicides started being used in the first place.  In the late 1990’s, growers were experiencing problems with dense stands of winter annual weeds such as chickweed that interfered with tillage and planting.  One contributor to this was the occasional reduced activity of spring-applied burndown herbicides in cool weather, which resulted in too slow death and dry down of weeds to prevent the problems the weeds caused.  Fall-applied herbicides became a solution to this, since they result in almost weedfree spring seedbeds up until the point when giant ragweed and other summer annuals emerge (early May for most of these).  As anyone knows who has used fall herbicides, their effectiveness reduces the overall importance of the spring-applied burndown, since it does not have to control a mess of large, overwintered weeds.  It’s all just way easier.    And issues with cold weather and spring-applied burndown herbicides are therefore less important.  For as little as $6 worth of fall-applied herbicide.  Something to think about moving forward.

Spraying with Drones

By John Fulton (Associate Professor), Chris Wiegman (graduate student), Erdal Ozkan ( Professor), and Scott Shearer (Professor), Ohio State University Department of Food, Agricultural and Biological Engineering

Drones or Unmanned Aircraft Systems (UAS) have become a common technology in agriculture. As of early 2019, there were around 1.3 million registered drones in the U.S. and over 116,000 registered drone operators within the commercial sector. Within agriculture, drones have been mainly used for scouting purposes. Today, uses of drones include collecting remotely sensed imagery, tissues samples, and water samples. Spraying with drones is also available through some manufacturers.

Drone spraying has been used Southeast Asian countries such as China, Japan and South Korea for several decades. In fact, the use of this type of spraying in Japan can be traced back to the 90’s. Currently, we are seeing a significant increase in the number of drones used in these countries, mostly in rice production that requires applications done when the field is flooded with water, making entry of motorized vehicle to the field impractical. Drone spraying has also been considered as the most effective and safe way to treat crops grown in steep hills.

Drone spraying is becoming increasingly available for specialty crops and row-crop production. Here is the U.S., drone spraying was approved in 2015, but under strict policies in the state of California. The Yamaha RMAX from Japan was the first drone sprayer tested in California prior to approval. Most recently, drone manufacturers such as DJI (https://www.dji.com/) have started offering high payload rotor drones that include sprayers. Spray applications using drones has arrived in Ohio as well.

Spraying with drones is a unique practice since it is conducted autonomously. Drone sprayers are equipped with almost all the parts of any other sprayer: a tank, a pump to push liquid through the hoses to the nozzles, filters and a pressure gauge. But there are limitations, mostly on the size of these components because of the power required to keep the drone sprayer in flight mode for a reasonable time.

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Preemergence Herbicide Application Timings: Pros and Cons

Source: Bob Hartzler,  Integrated Crop Management News, and Iowa State University Extension and Outreach.

Preemergence herbicides are the foundation of herbicide-based weed management systems, and effective use of these products is essential to protect crop yields and reduce selection pressure for herbicide resistant weeds. In a perfect world, applying preemergence herbicides immediately after planting would provide the greatest likelihood of maximum performance, but equipment and labor availability limit many farms from using this approach. This article will provide a brief overview of the pros and cons of different application strategies.

Early preplant: Applications made more than 7 to 10 days prior to planting.
Pros Cons
  • Applications typically completed before summer annual weeds begin to germinate, thus increasing the likelihood of timely activation by rainfall.
  • May provide a weed-free seedbed at planting. In no-till systems, include a burndown product to control emerged winter annual and other weeds.
  • Application completed before planting, spreading workload.
  • Residual activity into the growing season is shorter than when product is applied near planting. Use of layered residual (including a residual with postemergence application) approach reduces this risk.
  • Final seedbed preparation tillage may ‘dilute’ the herbicide within the soil profile if tool is run too deep, and may result in uneven distribution of the herbicide.
  • Planter units may move herbicide out of the crop row, allowing weed escapes
  • If planting is delayed, much of the value of the herbicide may be lost.

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