By Tom Barber, Extension Weed Scientist
Cotton acres are likely to increase this year, and I have talked to a couple that are growing cotton for the first time so it appears cotton is making a comeback! Several new technologies are available now that weren’t 5 years ago but regardless of the variety or technology planted, residuals for pigweed control will continue to be critical for success in cotton. New technologies are good but managing pigweed is a numbers game and you have to start off with reduced numbers for any POST application to be effective. Additionally residuals at planting buy valuable weed-free time for cotton emergence and seedling development which is important for maximized yields.
Treflan or Prowl (yellow herbicides) incorporated were for many years what we started with for cotton weed control. Some growers still use these products. They are best when incorporated, but keep in mind many populations of pigweed in Arkansas are also resistant to this class of chemistry, so neither are stand-alone options in cotton.
Cotoran, Caporol or Diuron (Direx) have for a long time been the standard for PRE applications. These are also the products we used, in addition to the yellows mentioned earlier, prior to the introduction of Roundup Ready cotton, so they have been around for a while but they still work. Potential cotton injury is the number one complaint following applications of any of these products and each should be put out based on the soil type rate listed on the label and in the MP44. Yes they can all cause injury, diuron potentially the most especially on sandy soils, but they are needed for a good start in fields heavily infested with pigweed.
Warrant is another option PRE, that I get a lot of questions about and recommend from time to time especially on sandy ground where rates of Cotoran etc. have to be reduced to lower than effective levels due to injury concerns. The problem with Warrant is it can be inconsistent depending on environmental conditions. Under cool conditions, the capsule does not break down as fast, thus control is reduced.
Reflex (fomesafen) pre-plant is still a good option as long as pigweed populations are not PPO-resistant. Through our research at Marion, Reflex did not provide much control even at higher rates on PPO-resistant pigweed populations. South Arkansas may be the only fit for Reflex pre-plant given the current status of PPO-resistance. To prevent injury from Reflex it is recommended that applications be made prior to planting and planting should not occur until 0.5 inch rain received.
This brings us to Brake. Last year Brake FX was probably the most broad-spectrum PRE that we evaluated in our plots. In addition, residual control lasted 2-3 weeks longer than any other product evaluated at planting. Brake FX is a pre-mix of fluridone and Cotoran. This year Brake will only be marketed as a stand-alone product, meaning no mixtures with other herbicides. The good news is Brake will be less expensive; the bad news is we will need to mix something with it because Brake by itself at rates needed for crop rotation is not enough for extended pigweed control. Best options for mixing would be Brake 16-21oz/A plus 24oz Cotoran, 24oz Caparol or 16oz diuron. Brake does require more rainfall for activation, this is another reason to mix something with it that requires less rainfall to activate. If frequent rainfall continues this option will be well worth the money. If it turns dry it will not be as effective. Either way I would consider using Brake combinations PRE, especially on fields high in pigweed numbers.