The question of the week is will the Palmer amaranth die that is still green after an Engenia or Xtendimax application? The situation is that many pigweeds in some fields have not grown after an Engenia or Xtendimax application but still remain green going on 10 days or more after the application. The question is will these pigweeds start to regrow?
In answering this question, I think we can draw from our wealth of experience with horseweed and dicamba. We are all familiar with the situation where horseweed remains green but will not grow for several weeks after a dicamba application. Often the stems of some of the horseweed will start to rot and those plants will eventually die. In more recent years some horseweed has recovered about 10 days after the dicamba application and will start to regrow.
I have seen this happen as well with Palmer amaranth after an application of either Engenia, Xtendimax or Clarity. Often the Palmer that go on to eventually die will, upon closer examination, start showing a rotten stem about 10 days after the dicamba application. In some cases, it is 3 weeks or more before some of these Palmer amaranth are actually controlled.
A fairly small percentage in research has regrown after application. In those cases, if Palmer amaranth has not started to show some regrowth 14 days after application, they typically have been controlled.
We are still early in assessing how effective dicamba will be on Palmer amaranth across Tennessee. Experience as well as some data would suggest that control of Palmer amaranth by dicamba may vary by location. For example, studies from 2016 to 2010 with dicamba on pigweed in different locations has shown that better control with one application is typically achieved here at Jackson (>90%) compared to research we have done west of Millington (70 to 80%). In looking at that data nozzle type nor dicamba formulation made any difference on control.
Regardless of location, a follow-up application of Liberty applied 7 to 10 days after the first Engenia or Xtendimax application has worked well taking out the crippled Palmer amaranth in cotton. In Xtend soybean our research at Jackson has shown good Palmer control with a sequential application of Engenia or Xtendimax applied 10 to 14 days after the first application.