University of Georgia Weed Scientist Stanley Culpepper knows growers have Palmer amaranth in their cotton fields. He sees it every day.
"For those growers not using residual based programs, this result continues to be expected," Culpepper says. "Unfortunately, there are also growers using sound residual programs that are facing this late-season pigweed challenge. For large pigweeds, the P&P program (Plowing and Pulling) is often the only consistently effective option, albeit not really an economical option for sure."
For those using P&P, Culpepper cautions that the job isn't done until the weeds are taken from the field.
"They will re-root once it rains!" Culpepper says.
However, for timely treatment Culpepper reported the following herbicide options in the UGA Cotton Newsletter this month.
1) Diuron (Direx, others) + MSMA has proven time and time again to be one of the most effective and economical treatments when spraying pigweeds 4 inches or smaller in size. Below are several key factors to consider prior to spraying diuron + MSMA in cotton.
Diuron rate: 1.6 to 2.4 pt/A, see label for use on your soils, cotton must be 12 inches tall.
Check label for rotational restrictions as your next crop may be sensitive.
MSMA rate: 2.5 pt of a 6.6 lb ai per gal or 2.67 pt of a 6.0 lb ai per gal.
Add Crop Oil when applying diuron + MSMA alone.
The addition of Valor to this mixture will not improve control of emerged Palmer but will improve residual control, especially if rainfall does not occur within 7 days of application. If adding Valor to a diuron + MSMA mixture one must use surfactant and not crop oil. Never apply Valor with crop oil at layby.
A weakness of diuron + MSMA is controlling larger morningglory (> 4 inch). The addition of Aim, ET, or Valor to diuron + MSMA will improve control.
Valor, Aim, and ET should only be applied to cotton that is at least 18 inches tall having 3-4 inches of a "barky" stem. Spray should not contact higher than 2 inches up on the cotton.
These mixtures will be far more effective when applied in 15 to 20 gallons of water per acre when compared to lower volumes such as 10 gallons per acre.
2. Paraquat (38 fl oz of Gramoxone Inteon) + diuron (1.6 to 2.4 pt) + Crop Oil is the single most effective herbicide mixture to control emerged Palmer amaranth, Culpepper says, noting this treatment often controls Palmer up to 8 inches in size if applied appropriately. However, he notes several key factors to consider before spraying this mixture in cotton.
Hooded application only.
Spray or even spray drift can not contact any part of the cotton or very, very serious injury will occur.
Of course, this application will not control weeds in the cotton row.
Apply in 15 to 20 gallon of water per acre.
See label for use of diuron on your soil.