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Consider planting conditions when choosing preemergence herbicides

• By Charlie Cahoon Jr. •

According to the most recent Cotton Planting Conditions Forecast, planting conditions should improve by next Wednesday, May 13, 2020. For those itching to start earlier in the week, I hope you consider how marginal planting conditions can influence cotton response to preemergence herbicides.

Cool, wet conditions can influence cotton tolerance to all residual herbicides. However, with the persisting cool weather, I have been leaving one herbicide out of my recommendations for those planting in less than ideal conditions – Warrant.

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Warrant is an encapsulated formulation of the herbicide acetochlor, allowing the herbicide to be used preemergence or postemergence to cotton. However, if cotton germination is slowed due to cool and/or wet soils, Warrant applied preemergence can injure cotton. Injury is often superficial with no yield reductions, but it is better not compound the issue of poor planting conditions with herbicide injury.

et me be clear, this is not permission to drop preemergence herbicides altogether; at-planting residual herbicides are the foundation for successful weed management in all crops.

With marginal planting conditions, Reflex + Direx or Reflex + Brake would be great choices where herbicide-resistant Palmer amaranth persists. If common ragweed is the weed of concern, combinations including Cotoran (Cotoran + Reflex or Brake + Cotoran) would be in order.

cotton injury from warrant

Cotton injury resulting from Warrant applied 1 week prior to planting (right) compared to nontreated (left). Warrant should not be used prior to planting, unless immediately before planting — photo by Andrew Blythe.

Once planting conditions improve, Warrant combinations (Warrant + Reflex, Warrant + Direx, or Warrant + Cotoran) will work well on most broadleaf weeds and annual grasses. Alternatively, if you decide to avoid Warrant preemergence, consider adding one of the Group 15 herbicides (Dual Magnum, Outlook or Warrant) early postemergence.

Dr. Charlie Cahoon Jr. is an Extension weed specialist and assistant professor with North Carolina State University. He may be reached at cwcahoon@ncsu.edu