Weed control is everything in a cotton crop. A tropical perennial grown as a summer annual crop in the U.S., cotton is often at a disadvantage when taking on the weeds we find in the Southern United States.
So, you start off with the appropriate steps: you pick a seed trait package that gives you the most opportunities for weed management; you burndown preplant; you make sure to include a product with residual control.
However, even after planting, cotton still needs 8 weeks of weed-free growth to reach its maximum yield potential. Good yields require 95 percent weed control, while excellent yields require more like 99 percent control or better.
How can you make sure that your in-season herbicide applications give you the most control?
End weeds early
Liberty® is an effective tool for farmers who plant cotton varieties that are tolerant to Liberty herbicides, and glyphosate can be effective at controlling weeds in glyphosate-tolerant cotton. But in both cases, early control (when weeds are less than 3-4 inches tall) is essential.
Spraying weeds that are greater than 4 inches tall can lead to the spread of herbicide resistance, which is already a major concern. Timeliness is especially important with pigweeds, which can grow at a rate of 1 inch or more per day and spread more than 100,000 seeds.
In phenoxy-tolerant cotton, over the top phenoxies – such as Engenia®, Xtendimax®, Enlist One™ and Enlist Duo® – are also an option for controlling pigweeds and other difficult-to-manage weeds. Pay close attention to the label, as well as local, state and federal regulations, as to where and when these products can be used.
Take advantage of overlapping residuals
Even with the best burndown program – utilizing products such as Caparol®, Cotoran®, Direx® or Brake®- residual control eventually breaks down. That’s why overlapping residuals in subsequent post-emergence applications is an excellent way to ensure continued herbicide activity from burndown to canopy closure. It also allows for the rotation of modes of action within a growing season. Dual®, Warrant® and Outlook® are other options for use in the cotton crop, as they all provide excellent residual weed control.
Timing that first post-emergent application 14 to 21 days after at-planting application is also largely a good way to overlap residual activity. As counterintuitive as it may feel, it’s better to spray bare ground and keep residual control than to fight emerged weeds across the entire season.
Refer to all product labels for use rates, application guidelines and additional restrictions that may apply.