Across Arkansas, farmers are battling a formidable foe: herbicide-resistant pigweed. But its toughness can be blunted with proper control techniques, said Herb Ginn, Lawrence County agent for the University of Arkansas Division of Agriculture.
“Though pigweed is tough to fight, control is possible,” he said.
Pigweed is a difficult foe for many reasons. It quickly developed a fierce resistance to glyphosate, the weed can produce millions of seeds per acre, and it grows easily and everywhere. It’s tough, too – after reaching a certain maturity level, chemical control is impossible, prompting farmers to resort to an old weapon: hand-hoeing.
“This weed has many enemies, and few, if any, friends. It makes fields ugly, competes with valuable crops by consuming costly fertilizer and water, and robs yield. It can grow up to one inch a day, when conditions are right.”
There are a variety of control methods for pigweed.
When dealing with resistant weeds in soybeans, Ginn recommends starting out with a clean field by using tillage or a burn-down program. Make sure to put out a residual treatment of Prefix, Dual, Valor or Valor-containing pre-mix such as Valor XLT, Gangster or Envive.
Use Flexstar or Ultra Blazer at full rate from early-post to 3-4-inch pigweed. Rotate to LibertyLink soybeans and use Ignite in combination with one of the mentioned residual treatments.
With peanuts, there can be resistance to aceto-lactase synthase-inhibitor herbicides, or ALS. These herbicides kill weeds by preventing plants from producing essential amino acids needed for growth and development. In this case, there are several options.
One option is to use Prowl preplant incorporated, followed by Valor, followed by Cadre or Ultra Blazer and 2,4-DB on 3-inch or smaller pigweed. The other option consists of using Prowl preplant incorporated, followed by Paraquat, Storm and Dual at cracking, and then Cobra or Ultra Blazer and Dual Magnum on 3-inch or smaller pigweed.
A fact sheet is available here. 
For more information on weed control, contact your county agent or visit www.uaex.edu .