Rainfall has eliminated most herbicide carryover concern

Rich Keller, 11/13/2012


In much of the Midwest drought area of 2012, the rainfall that has fallen since soil residual herbicides were applied last spring until today has been enough to allow plant back with rotation crops without worry about carryover.

There has been some rainfall this fall in much of the Midwest, and depending on the residual herbicide used, there has been enough moisture since early spring that most residual herbicides have dissipated to a level of no or little concern for affecting a corn-soybean rotation or even a corn-wheat-soybean rotation, said Brent Philbrook, Bayer CropScience regional manager for field development of the northeast quarter of the U.S.

“The first thing I say is that you should always refer back to the product label because all companies have information relative to planting back to crops. Those tables and sections in the labels take into account certain extreme conditions, etc. On our labels, we put in a requirement for so many months to plant back but also expectations or exceptions for rainfall and supplemental irrigation,” said Philbrook.

“If you look at a Corvus or Balance Flexx label, they have wording relative to how much total precipitation you need so that the monthly plant-back rules apply. If you don’t get those moisture levels, you might extend that plant-back interval slightly,” he added. “People tend to focus on the chemistry used when considering residue, but the sensitivity of the following crop is as much if not more of a component of residual herbicide activity or presence.”

Jim Bloomberg, Bayer CropScience product development manager for corn and soybeans, fungicides and herbicides, noted that various products have different half lives, or time required for carryover potentialdissipating.

“For example, PPO chemistries take longer to break down in the soil. Some active ingredients, such as that in Corvus and Balance Flexx, have a shorter half-life and break down much more quickly,” Bloomberg said.

Bloomberg agrees with Philbrook in suggesting the product labels are the starting point, and he suggests there is other information in brochures and booklets. This look at information resources should provide the top line for whether a farmer needs to have any concern about persistence of a herbicide in the soil.

As far as Bloomberg is concerned, crop consultants and agricultural retailers and the whole supply chain have a chance to step up to assist farmers and establish a partnership bond with their customers.

“There is the potential for a lot of service orientation by ag retailers. Farmers are probably going to want to talk to their dealers and distributors and consult with whoever it might be to discuss their thoughts.”

He said, working together to make plans and find answers for next year is a “win-win situation for the channel and their customers.” There are proactive actions and discussions that should be considered if there are any worries. Bloomberg noted that being proactive in planning for 2013 could include:

  • Considering all of the products used the prior year, whether used in combination or sequence. Tankmix products may be more limiting than other herbicides.
  • Submitting soil samples to soil laboratories for bioassays to see if an active ingredient is still present to affect a sensitive rotation crop.
  • Looking for hybrids or cultivars that are a little more tolerant to a specific chemistry.
  • When planting season arrives, not planting until the seed bed is in the best possible condition, definitely not a cold and wet soil situation.
  • Setting up a simple soil assay using soils from treated and untreated soil, planting seed and putting the soil in a warm and sunny spot to grow and then evaluating the plants.



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