Of all the questions asked by peanut growers on effective weed control, tank mix questions are the most common and most difficult to answer.

University of Georgia Extension weed specialist Eric Prostko, right, discusses tank mix options with Ned French, product development manager for Amvac Chemical Corporation, during the 47th annual meeting of the American Peanut Research and Education Society in Charleston, S.C. in mid-July.

“Many peanut growers prefer to use tank-mixtures that contain multiple pesticides with the goal of reducing input costs. However, the multitude of possible tank-mixtures has not been adequately tested for crop response and efficacy,” said Eric Prostko, University of Georgia Extension weed specialist, in a paper presented at the American Peanut Research and Education Society meeting in Charleston, S.C. July 15.

As Prostko sees it, there are more than 91,000 potential spraying combinations growers can use.

“If you take somebody like myself, I do about 3,000 plots a year, so if I dropped everything else, it would take me 122 years to figure out all of these combinations, and I’m probably not going to live that long. It is very difficult thing to know for sure when a grower or an agent asks a question about tank mixes. Are we going to have a reduction in efficacy?  Are we going to have more crop response? There are a lot of things going on.”

To help answer some of the questions, the University of Georgia conducted research last year to assess the impact of adding 2, 4-DB to currently recommended post-emergence tank mixtures of Cadre (imazapic) plus Dual Magnum (s-metolachlor) or Warrant (acetochlor) and Cobra (lactofen) + Dual Magnum or Warrant.

Prostko explained that replicated, small-plot, weed-free trials were established in Tifton and Attapulgus to evaluate potential peanut yield losses associated with these tank mixtures. He noted that no interaction between timing and treatment was observed and neither timing nor herbicide treatment had a significant effect on peanut yield.

“Dual tank-mixtures were slightly more injurious (cosmetic) than Warrant tank mixtures,” he said.

In an additional replicated, small-plot weed control trial conducted in Tifton, herbicide

programs that included three-way tank-mixtures of Cobra 2EC or Ultra Blazer 2AS plus Dual Magnum provided excellent control of Palmer amaranth with peanut yields equivalent to current standards, according to Prostko.

In the meantime, Ted Webster, USDA-ARS research agronomist in Tifton, explained research to control purple nutusedge in Georgia peanuts. Purple nutsedge produces tubers that are a contaminant to peanuts. Webster’s research is seeking ways to minimize the contamination caused by tubers because they partake an off flavor when roasted and become like little rocks. 

“In order to effectively manage purple nutsedge populations, practices should control vegetation and minimize production of new tubers,” Webster said. “However, the influence of herbicides on purple nutsedge tubers has not been extensively evaluated.”

Webster said the objective of the research was to evaluate the effectiveness of imazapic on purple nutsedge foliar growth and tuber production. In the research, scientists took a single pre-spouted tuber and put it in outdoor micro plots in Tifton. The tubers were allowed to grow and establish for six weeks with seven different rates of imazapic applied. The shoots were marked as they emerged and the plants were allowed to grow for an additional seven weeks before the tubers were exhumed.

“The research shows that herbicides can be very important in halting tuber production and minimizing the contamination potential in our harvested peanuts,” Webster said. “Purple nutsedge is a perennial weed and s a perennial problem that we are going to have to tackle it and be consistent with our management programs.”