Managing Herbicide Carryover

Insights To Help Growers Increase Yields Through Better Crop Management


   Cool weather has been the major theme for most of May. We will see what the rest of June looks like, but overall this year has been characterized by cool and wet conditions all spring. Anytime an early weather pattern like this persists, the crop struggles and grows off slowly due to a lack of warm temperatures and sunlight. A struggling crop is susceptible to several issues including herbicide carryover.
   Resistant weed management in the North Delta has created some unique and sometimes challenging issues with crop rotation. We have received several calls asking about crop rotation intervals for nearly all crops since we have started using a multi-mode of action approach to resistant weed management.
Fomesafen carryover to grain sorghum and corn has been the most consistent herbicide carryover that we have seen to these grain crops the past few years. It is the active ingredient in many herbicides that are used to help control glyphosate-resistant broadleaf weeds, with palmer pigweed being the primary target. The compound is very active on palmer pigweed, and thus has been popular to apply postemergence in cotton and soybeans. This works well until we find carryover to grain crops the next spring.  

   Most of the issues we see are with late summer applications of fomesafen in cotton or soybeans. This application puts April and early May planted corn and grain sorghum close to the minimum 10 month rotation interval the following year. Some of the most consistent issues we see with carryover are with the use of one or a combination of stale seed beds, minimum tillage, cooler winters or springs, and sandy soil types.
   Sandy soils are the most consistent factor overall, and my hypothesis is that in sandier soils there is only a limited soil saturation period needed to break down fomesafen in the top two inches of the soil profile. Thus, fomesafen hangs around longer than expected when cooler temperatures persist throughout the spring. Typically, corn will grow through most damage fairly well with the exception of occasional overlaps.
   Grain soghum is usually more sensitive to early season fomesafen carryover than corn and therefore is less predictable. This is the primary option for resistant palmer pigweed control, so we expect to continue to see issues along the way.
   For more information about managing herbicide carryover, contact your local Pioneer representative. ∆
   GREG PFEFFER: Agronomist for Pioneer, Dexter, Missouri
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