I have gotten a number of reports and pictures from consultants on disappointing Palmer amaranth control from POST applications last week of Engenia, Liberty and XtendiMax. This is not surprising. Spraying those herbicides on Palmer amaranth that is 6 to 10 inches tall with frequent overcast skies and showers most every afternoon is a recipe for poor control.
Judging by some field calls, Engenia and XtendiMax need at least two hours of a rain-free period after application to provide good Palmer control.
Liberty has a four-hour rainfast period stated on the label, and it is abundantly clear this spring it needs every minute of it.
Indeed, I have seen less than ideal weed control with those herbicides in our research applied the last 10 days.
Engenia and XtendiMax was providing about 70 to 80 percent control of Palmer amaranth that was 6 to 12 inches tall. Liberty has been lucky to provide 30 percent Palmer amaranth control of that size pigweed with the cloud cover last week and frequent rain events.
Many fields will need to be retreated next week to remove the escaped Palmer amaranth. The good news is Palmer amaranth that is recovering from a dicamba application should be readily controlled with follow-up applications of either Engenia, XtendiMax, or Liberty in cotton. All these plus Flexstar are options in soybeans.
These applications should take place 10 to 14 days after the initial treatment.
Palmer amaranth that has escaped a Liberty application should be retreated within 10 days and ideally 7 days as fast as they look to be recovering.
There are some fields that have not been sprayed for the first time due to the weather. Palmer in some of these fields can readily be measured more efficiently with a yard stick and not a ruler. In order to control that large a Palmer amaranth a planned sequential application will need to be used. Ideally it should contain a combination of the herbicides mentioned above in order to be effective.