Burndown Herbicides for No-till Wheat

Source:  Mark Loux, OSU

Herbicide options for burndown of existing weeds prior to planting of no-till wheat include glyphosate, Gramoxone, Sharpen, and dicamba.  Among these, the combination of glyphosate and Sharpen probably provides the best combination of efficacy on marestail, flexibility in application timing and residual control.  Dicamba labels have the following restriction on preplant applications – “allow 10 days between application and planting for each 0.25 lb ai/A used”.  A rate of 0.5 lb ai/A would therefore need to be applied at least 20 days before planting.  We do not know of any 2,4-D product labels that support the use of 2,4-D prior to or at the time wheat planting.  There is some risk of stand reduction and injury to wheat from applications of 2,4-D too close to the time of planting.  Liberty and other glufosinate products are also not labeled for use as a burndown treatment for wheat.  Sharpen should provide limited residual control of winter annuals that emerge after herbicide application, and the rate can be increased from 1 to 2 oz/A to improve the length of residual.  Gramoxone should also effectively control small seedlings of marestail and other winter annuals.  Be sure to use the appropriate adjuvants with any of these, and increase spray volume to 15 to 20 gpa to ensure adequate coverage with Sharpen or Gramoxone.

There are several effective postemergence herbicide treatments for wheat that can be applied in November to control these weeds, in fields where preplant burndown treatments are not used.  The most effective postemergence treatments include Huskie, Quelex, or mixtures of dicamba with either Peak, tribenuron (Express etc), or a tribenuron/thifensulfuron premix (Harmony Xtra etc).  We discourage application of 2,4-D to emerged wheat in the fall due to the risk of injury and yield reduction.

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.

Mid-Season Weed Management in Soybeans – Hot, Dry Edition

Source: Mark Loux, OSU

A few weed-related observations while we try to stay cool and hope for a day of rain or at least popup thunderstorms.

 

  • One of the frequent questions during extended dry weather is – do I wait for rain before applying POST herbicides, or just go ahead and apply before the weeds get any larger and tougher to control.  Our experience has been that it’s best to go ahead and apply when weeds are still small, even if it’s dry, and herbicides will usually do what they are supposed to.  Letting them get larger without any sure forecast for rain can make for a tough situation that requires higher rates or a more injurious mix.  On the other hand, waiting to apply can be fine if there is a good chance of rain within the next few days.  It’s not always an easy decision.
  • The deadline for applying dicamba to Xtend soybeans was June 30.  Tavium can still be applied where the soybeans were planted less than 45 days ago and have not exceeded V4, an alternative to dicamba will have to be used.  We should point out that very hot days and warm nights are not appropriate conditions for applying dicamba anyway.
  • The replacement for dicamba on Xtend soybeans is usually going to be glyphosate or a mix of glyphosate with either fomesafen (Flexstar, etc), Cobra/Phoenix, or Ultra Blazer.  Will they cause soybean injury?  Yes.  Will the injury be worse under hot conditions?  Probably.  Do you want weed control?  We assume yes.  Using a less aggressive adjuvant approach can reduce the injury.  Example – applying fomesafen with MSO + AMS will be less injurious than COC + UAN.  Be sure to use adjuvants appropriate for the weed species and size though.
  • Applying POST herbicides early or late in the day may have some potential to reduce injury.  Keep in mind however that the activity of most POST herbicides on weeds is reduced during overnight hours.  In previous OSU research where we applied herbicides at 3-hour intervals from 6 am to 9 pm, activity was substantially reduced from 9 pm through 6 am.  So activity was decreasing after 6 pm and ramping back up after 6 am.  Our studies included fomesafen, glyphosate, Firstrate, 2,4-D, and glufosinate.  Of these herbicides, 2,4-D was the only one not affected by time of day.   Giant ragweed was the only broadleaf weed in the 2,4-D study, which occurred in wheat stubble.

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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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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.

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