Small Palmer Amaranth Escapes in Soybean and Late Liberty Application in Cotton

Judging by looking at fields last week as well as quite a few phone calls the last couple of days it is clear that Palmer amaranth is kicking our tail in a number of soybean and a few cotton fields. A good number of calls have been from frustrated consultants, county agents or retailers who have seen Palmer amaranth recover that was only 1 to 2” when a PPO herbicide(Flexstar, Prefix, Cobra, Ultra Blaze) was applied.

Often these folks question whether Palmer amaranth has become resistant to PPO herbicides? We continue to screen for this but to date have not found any resistance. The truth is that the PPO herbicides even in their best working environment will barely provide adequate control of even 1 to 2” Palmer. If the Palmer is thick which makes good spray coverage tough or if the Palmer is a little hardened off from heat or drought the PPO herbicides will only provide about 60% control. In other words resistance and just natural tolerance to post applications of PPO herbicides is a razor thin difference. As a result the best management practice to control Palmer is never let it emerge.

The only real option to manage these small Palmer that escaped a PPO herbicide is to come back with another application of a PPO herbicide 5 or so days later. Do not expect great control with this follow up application. However, it will stunt them some and give the soybeans a chance.

The other call has come from folks asking if they can apply a 3^rd Liberty application over the top of PHY 375 or PHY 499. My answer is no! We have done this number of times in research and have always reduced the cotton yield by 200 plus lbs and delayed it a good week. The best option is get the hoods out where a number of very effective Palmer amaranth herbicides can be applied and not set the cotton back. Several have mentioned that MSMA has become short in supply. If that is not an option then herbicides like glyphosate tankmixed with diuron or prometryn (Caparol, Cotton Pro) would be a good substitution. Another good option is Liberty under the hood.