Cotton stalk destruction is a topic of research that has been evaluated for a good 20 to 25 years. Herbicides have been applied to conventional and Roundup Ready Cotton, focusing on the traditional active ingredients such as 2,4-D and dicamba.
The gold standard has been applying 1 quart/acre of a 4lb/gallon a.i. 2,4-D amine product immediately afterwards through two weeks after shredding stalks. This practice has yielded better than 90% control for decades.
With an increase in adoption of the dicamba and/or 2,4-D tolerant cotton varieties in 2017 and 2018 and with harvest upon us, chemical selection for cotton stalk destruction is a current topic of discussion. For Enlist, (2,4-D tolerant) cotton, 2,4-D is no longer an option to chemically destroy cotton stalks.
Stalk Destruction Options for Enlist Cotton
For cotton growers with Enlist (2,4-D tolerant) cotton, they will now have the choice of using either dichlorprop or dicamba to control cotton stalks. I received word on July 25th from TDA that a 24(c) Special Local Need label has been approved for a dichlorprop-containing product called Duplosan by NuFarm. Here’s a link to the label and this links to the special local needs information.
This product will be equally effective on cotton varieties with the XtendFlex or Glytol LibertyLink traits. Data compiled by AgriLife Extension shows that this product will be more effective than dicamba for controlling Enlist cotton.
The Duplosan label calls for a use rate of 32-48 fl oz/acre. Make notice that when using Duplosan for cotton stalk destruction, Duplosan should be applied to cotton stalks with some leaf regrowth. Applications of Duplosan made to freshly mowed stalks may be less effective.
Please note that Duplosan is an ester formulation, so special care will need to be taken if susceptible plants are nearby as volatilization is likely. Also note that this product is a state limited-use pesticide, thus you must be a licensed pesticide applicator or be working under the direct supervision of a licensed applicator to purchase or apply this product.
What does Duplosan cost per acre? I did a little research, getting quotes from only two local distributors. Approximate cost is $39.60 per gallon. With the labeled use rates, this equates to $9.90 to $14.85 per acre for Duplosan.
Stalk Destruction Options for Xtendflex Cotton Varieties
For Xtendflex (dicamba tolerant) cotton varieties, the old gold standard of 2,4-D amine is still a valid option for cotton stalk destruction, costing generally less than $5.00 per acre for 2,4-D amine.
To obtain optimum results, cotton stalks should be shredded (6 to 8 inch height) and the spray application made soon after shredding. Best results are achieved if the herbicide is applied the same day as the shredding operation.
The first application should be at the rate of one pound of active ingredient per acre (for example, 1 quart of a 4 lb/gallon formulation). Generally, a second application of 0.5 to 1.0 pound active ingredient per acre will be necessary to control live stalks and emerged cotton seedlings.
To achieve optimum effectiveness, some growers have mounted spray booms directly on their flail shredders and banding the herbicide during the shredding operation, and achieving excellent results. Thorough coverage is essential, and should be in the range of 5 to 10 gallons of water per acre.
Also, the addition of surfactant at the rate of 0.5 percent v/v (2 quarts per 100 gallons of water) is recommended. In a 2010 study conducted at the Texas AgriLife Research and Extension Center, there was essentially no difference in killing re-growing cotton plants with 2,4-D between treating shredded stalks or those or left standing.
We also know from previous research that waiting 21 days after shredding cotton stalks has not been as effective with 2,4-D.