• By Larry Steckel •
This week will be the start of the early postemergence applications in cotton. These applications are often critical to not only curtail weed competition but to combat thrips injury as well.
The biggest concern with these applications is injury to the young cotton plants. Traditionally, the main pesticides applied are a mixture of glyphosate plus either Dual, Outlook or Warrant plus acephate. Those herbicides, which contain a good surfactant in glyphosate with the oil formulations of the chloracetamide herbicides, will always burn young cotton leaves. The typical cotton injury will range from 10 to 20%.
The acephate that is often tankmixed with these herbicides will typically not add to the cotton injury. However, in recent years, more injury is seen from adding dicamba to this tankmix in Xtend cotton. My experience has been to expect another 5% to 10% injury when XtendiMax or Engenia is applied in a mixture with the herbicides mentioned above.
On top of the typical cotton injury seen with those tankmixtures, all the scattered showers in the forecast for the next 10 days can cause frequent weather delays where sprayers are often sitting loaded for hours or even days.
Herbicides like Dual, Outlook and Warrant, as soon as the agitation is shut-off, are prone to settling to the bottom of the spray tank. Then when the sprayer is cranked up and the application begins, an extremely stout rate of the chloracetamide herbicide will be sprayed for a good part of the tank load.
Spend time re-agitating the tank
This can cause extreme burn. So what is the answer to this problem?
The best solution I have learned from a very experienced sprayer operator is to spend a good while re-agitating the tank. Then when you think you have done it long enough, spend a good bit more time agitating the tank.
The weather delays can cause issues in more ways than one. Some applicators in a hurry to load a sprayer will add multiple herbicides, adjuvants and often insecticides all together into the induction tank with no water.
If pumped directly into the spray tank in one big glob, they often will not disperse in the tank but settle to the bottom. All those products settled at the bottom are the first to be sprayed and at a much higher rate than intended, resulting in injured cotton for much of that tank full.
In our research, we do not see as much injury as what is often seen in the field as we mix them one at a time in water. That would be the solution here as well.
Load some water, then each product into the spray tank one at a time instead of mixing all the products together by themselves, then putting them into the sprayer tank in one big batch.
Dr. Larry Steckel is a University of Tennessee Extension weed specialist. He may be reached at firstname.lastname@example.org.