Calls coming in from folks this past weekend and even Monday reported the height of the Palmer amaranth in their fields in inches. Just two days later (Wednesday) more pigweed calls came in and the description of the Palmer amaranth height was given in feet! There are no easy answers on what to do with 1.5 to 2 foot tall Palmer amaranth that will likely be near 3’ when some fields can be sprayed.
Never the less, I will try to provide some. First calls were from folks who have Liberty Link soybeans wondering if Liberty will control a 2 or even 3’ tall Palmer? In our research as well as others in the Mid-South the answer is yes, but how the Liberty is applied is critical to success. The key to controlling very large Palmer with Liberty is that it must be applied in a sequential program (32 oz/A each time) about 7 days apart. If applications are delayed even as much as 10 days apart control typically suffers. In other words it would be better to go a day early than a couple days late on the second application.
Moreover these Liberty applications need to be made in the middle of the day. Certainly no earlier than 9:00 a.m. and no later than 6:00 pm. Utilize 20 gallons per acre of water and spray with twin orifice nozzles like a TADX. The old single orifice flat fan should do a decent job as well. The main thing is to get as good of coverage as possible which means do not spray with a coarse droplet size nozzle.
What about Roundup Ready or conventional soybeans? I have no real good rescue treatment to recommend. In some cases disking up and replanting maybe the way to go. If you till those large pigweed be sure to do a thorough job. All too often I have seen tall Palmer get tilled where part of the plant is buried and partially cut up. These plants are impossible to control with even Gramoxone as they recover.