Most of the fields I have been in this week have a flush of weeds. It is likely the heavy rainfall has washed our pre-emergence herbicides out. We are dealing with 3”+ tall pigweed, horse weed and morning glories.
Steve Li, Extension Weed Scientist, suggests using Liberty + Dual Magnum or Liberty +Warrant in cotton due to wide occurrence and infestations of herbicide-resistant pigweeds. The first true leaf needs to be fully expanded to apply Dual Magnum or Warrant over the top. In some situations when applying Dual Magnum or Warrant is not possible (e.g., seedlings are too small or thrips damage is too bad), apply Liberty by itself to avoid unacceptable cotton injury and move 2nd POST early.
Herbicide Resistance Info
Under normal growing conditions, cotton may receive minor leaf burn caused by Dual Magnum or Warrant and will grow out of it in 7-14 days. Overlapping residual herbicides is the basis to achieve successful season-long weed control. Always spray Liberty with at least 15 GPA output and medium droplet size to ensure good coverage.
If you do not have pigweed and horse weed, or they are still sensitive to glyphosate and ALS herbicides, another option is Roundup+Envoke (good on nutgrass but must be 5th true leaf cotton to apply) or Roundup + Staple (good on morning glories except small flower). Do not spray these combinations more than once a year to prevent weed resistance. Use Roundup + Dual magnum or Warrant in other POST applications.
We also have the new dicamba and 2,4-D technology. However if pigweeds are taller than 6 inches, a separate follow up application of Liberty may be required to increase control efficacy. Spray dicamba or 2,4-D first and follow up with Liberty 2-3 days later. Use label recommended practices to reduce auxin herbicide drift and off-target movement.
Always read and follow the label.