It was a wet winter in most of the Southern states, and although producers welcome the replenishing of the soil moisture profile, field conditions made certain cultural practices impossible. That could have a negative effect on the battle against Palmer amaranth, causing farmers to rely more heavily on residual herbicides and to make timely post applications.
Jared Whitaker, University of Georgia Extension cotton agronomist, says the wet winter and early spring may have affected some producers who wanted to utilize heavy cover crops and/or deep tillage to reduce Palmer emergence this spring.
“In a lot of places, it was far too wet for most of the year to deep-till, and many growers weren’t able to plant and grow cover crops,” he says.
Whitaker says research by Stanley Culpepper, UGA Extension weed scientist, has shown that these cultural practices can be effective.
Control What You Can’t See
Other control methods involve the critical pre-plant and pre-emergence applications of residual herbicides.
Producers who have glyphosate-resistant Palmer amaranth are relying on residual herbicides at pre-plant as well as pre-emergence this growing season, says Jason Norsworthy, associate professor of crop, soil and environmental sciences in the University of Arkansas’ Division of Agriculture.
“Producers are sometimes reluctant to apply herbicides when they cannot physically see Palmer amaranth in the field,” he says. “However, our data suggests that once Palmer amaranth emerges, it will be more difficult, if not impossible, to control, especially if it is glyphosate-resistant and ALS (Staple/Envoke) resistant.”
Don’t Wait Too Late
What moisture there is still left in the soil profile is likely to help with the activation of the residual herbicides, and because it has stopped raining so frequently, producers should be able to apply postemergence products in a timely manner.
“A farmer just commented that he’s going ahead on his dryland corn and make his post-herbicide application before the soil dries anymore,” says Rome Ethredge, who is the Seminole County Extension coordinator in Donalsonville, Ga.
“Residual herbicides need to be in the soil solution to get to the weed or weed seed in most cases for pre-emergence control, but the weeds need to be actively growing for postemergence herbicides to work their best.”
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