For essentially two decades, Georgia farmers have battled glyphosate-resistant
Palmer amaranth. Its impact on Georgia agriculture is so high it is simply immeasurable. As many lessons have been learned from our past, weed management decision making has vastly improved at all levels across Georgia. However there are great concerns with overuse of many herbicide chemistries especially dicamba and the PPO herbicides (examples such as Reflex, Cobra, Ultra Blazer, Valor, etc). With Georgia research, observations of pigweeds responding to dicamba applied by researchers has noted some plants dying while others show few symptoms (all plants of the same size and coverage). There is no question that this is a sign of trouble. Dr. Larry Steckle recently published an article addressing a similar concern with dicamba.
The picture above shows “Response of Palmer amaranth to 0.5 lbs/A of Dicamba: 2001 collected seed Left and 2019 collected seed Right. 11 days after application”.
What about the PPO herbicides? Although it is complex for a scientist to be able to say a weed is resistant to a specific herbicide, we now have the data required to make that statement. Palmer amaranth resistant to topical applications of PPO herbicides are in Georgia.
The photo (above) of plants dead (left) are from a known sensitive population treated with Reflex at 24 oz/A plus surfactant in the greenhouse. The plants surviving (right) were treated at the same time with 240, yes 240, oz/A of Reflex plus surfactant; plants were also not controlled with Cobra or Ultra Blazer at enormous rates. It is important to note, the world of weed control in Georgia is not ending as most growers are making and implementing sound management programs. However, there are a few that need a wakeup call………..hopefully this information will fulfill that need!!! Make good decisions, use cover crops or tillage, start clean, two residual at-plant herbicides, make sure your program includes at least 5 different classes of herbicide chemistry AND PULL OUT ESCAPES! Also stay in touch with your local extension for the best management programs.