Palmer pigweed rescue options in beans, cotton

The following article appeared on our main web site last July:

By Larry Steckel

University of Tennessee Extension Weed Specialist

July 3, 2009

Glyphosate-Resistant Palmer Amaranth Rescue Treatments in Soybean.

The calls have been coming in on what to do with Palmer amaranth that has survived high rates of glyphosate or glyphosate plus a PPO herbicide (Flexstar, Cadet, etc). This Palmer amaranth is typically 8 to 12 inches tall.

16 oz/A Flexstar + 2 oz/A 2,4DB

16 oz/A Flexstar

Gramoxone + Valor Hooded Application

Unfortunately, I do not have any silver bullets! I have tried several rescue treatments which include 16 oz/A Flexstar, 8 oz/A Flexstar, 0.6 oz/A Cadet, or 2 oz/A 2,4-DB. None of these treatments alone provided a satisfactory level of control of escaped Palmer amaranth. However, when I tankmixed 16 oz/A Flexstar with either 0.6 oz/A Cadet or 2 oz/A 2,4-DB it appeared 5 days after application that we were able to improve control from 50% to 70% of escaped larger Palmer. We will continue to monitor regrowth of these treatments next week.

I know that having 30% surviving GR Palmer amaranth is way too many in most cases but when GR Palmer amaranth gets some size, we are in a rescue mode.

The goal is having some soybeans to harvest this fall. It is way too late to stop yield loss from competition.

Glyphosate-Resistant Palmer Amaranth Rescue Treatments in Cotton.

Questions on good hooded or post direct treatments for Palmer amaranth have been common this week. When glyphosate will no longer provide Palmer control the only option is to use some of the very hot hooded applications that were common 10 years ago. The best GR Palmer amaranth hooded application I know of is 32 oz/A of Gramoxone Inteon + 1 oz of Valor + 0.25% crop oil (Picture Right). This is obviously a very hot mixture. Some other options that have worked well on GR Palmer amaranth are listed below:

Direx 32 oz/A + Valor 1.5 to 2 oz/A + MSMA 2.67 pt/A or Glyphosate 0.75 lbs ae/A:

Cotton should have 4” of bark to reduce chances of cotton stem injury.

• Advantages: Good burndown and residual pigweed control. Direx + Valor tankmix can burndown large GR Palmer as well.
• Considerations: MSMA should be the tank-mix of choice with Valor in fields where GR Palmer is present. Sloppy post-direct of Valor will burn cotton leaves.

Layby Pro 1 qt/A – Equivalent to 16 oz/A of Direx + 16 oz/A of Linex.

Add one percent crop oil for better control.

• Advantages: Good control of many grasses and broadleaves including pigweeds and morningglories. This premix will provide some residual pigweed control.
• Considerations: This premix can be weak on grasses. The addition of MSMA 2.67 pt/A of 6L formulation or glyphosate at 0.75 lb ae/A will control grasses. Sloppy post-direct of Linex will burn cotton leaves.

Ignite 280 29 oz/A

Cotton must be at least 6” tall.

• Advantages: Will cause little crop injury if cotton is a WideStrike variety. Ignite can control tall horseweed and giant ragweed. It provides good control of many broadleaf weeds including morninglories and GR Palmer up to 8” tall.
• Considerations: Some regrowth of large Palmer pigweeds can happen. Aim may be tankmixed with Ignite to improve burndown of large pigweeds. Ignite will offer no residual control. Caparol may be tankmixed with Ignite to provide residual pigweed control.

Caparol 32 oz/A + MSMA 2.67 pt/A or Glyphosate 0.75 lbs ae/A

Cotton must be at least 6” tall.

• Advantages: Causes less injury than some other tankmixes and is also economical. The Caparol + MSMA mixture has taken out some GR Palmer in past years if they were smaller than 6”. Caparol will provide good residual control of pigweed and horseweed.
• Considerations: Caparol and MSMA or glyphosate tankmixtures need good agitation to stay in suspension.