Rain has hampered field work this winter and early spring, including early burndown. As we near time to plant cotton, flexibility in burndown strategies will be required to make sure label requirements are followed and cotton seedlings are not damaged by herbicide. There are several situations with different weed issues that will be addressed here.
Horseweed and Palmer amaranth. This is a more traditional burn down situation that focuses on postemergence control of horseweed and preemergence control of Palmer pigweed. While excellent control of horseweed can be obtained in-season with Enlist Duo® or Enlist One™ + glufosinate, cleaning up fall-emerged horseweed while they are small with the burndown application is the preferred option. Enlist Duo at 2 qts provides broad-spectrum burndown of winter weeds including horseweed.
Several residual products can be applied along with the burndown to provide residual control of weeds until planting. Leadoff (1.5 oz) can be applied up to 30 days before planting. Fomesafen (1.0 pt) can be applied up to 21 days before planting. Flumioxazin can be applied at multiple rates, each with different waiting periods before planting. In no-till situations, 1 oz can be applied up to 14 days before planting and 1.5-2.0 oz has a 21-waiting period before planting. In conventional tillage fields, 1-2 oz must be applied at least 30 days before planting. Diuron (1 pt) provides the most flexibility in the burndown since it can be applied up to preemergence.
Italian ryegrass, annual bluegrass and other annual grass weeds. In situations where grasses are the main concern switching to a burndown of glyphosate and clethodim for control is the best option. Depending on the formulation of clethodim, the use rate will vary from 8 oz for a 2-pound formulation to 5.3 oz for a 3-pound formulation. Stay away from dicamba in these burndown situations since it antagonizes grass control. Residuals that can fit well in this situation include Brake (1 pt), pendimethalin (2 pt), Diuron (1 pt), or acetochlor (1.5 pt). Choose a residual that fits with your plans for preemergence and early postemergence herbicide programs.
Controlling weeds at the time of planting is a critical step to having a successful weed management program. Most applications at planting should include paraquat, plus a residual product. Paraquat is essential to kill small weeds after the planter goes through the field. Choosing a residual product at this time should target your most prevalent weeds species, but also take into consideration any residual product that was used during burndown.
If broadleaf weeds were the focus during burndown, perhaps focusing on a residual product from the earlier paragraph for grass control would be the best option at this time. Likewise, if grasses were the focus during burndown, broadleaf weeds should now be the focus. Adding Prometryn (1 pt) plus Fluometuron (1 pt) to Paraquat is an effective and popular option. An effective residual product at planting should provide adequate weed control until your cotton crop is ready for postemergence herbicide applications.
Future editions of Cotton Confidential will address crop herbicide application options with Enlist Duo® and Enlist One™ herbicides.