The most important weed management tool an Oklahoma peanut farmer should keep in his pickup just might be something as simple as a 50-cent ruler.

Timing post-emergent herbicide applications is extremely important for weed control, says Oklahoma State University Extension weed specialist Joe Armstrong.

“Peanut farmers need to treat weeds when they are four inches tall or less,” Armstrong advised during a recent production seminar at the annual Oklahoma Peanut Expo at the Quartz Mountain Resort near Lone Wolf. “When weeds average four inches high is the best time to spray,” he said.

A second essential tool is a spray rig. “Owning your own sprayer helps assure timely application. You don’t have to rely on someone else.”

Armstrong said weed control remains a challenging prospect for Oklahoma peanut producers. “We have some good pre-emergence herbicides available, but we have nothing new.”

He said a good pre-emergence herbicide program is essential for effective weed management. ‘”Pre-emergence herbicides are valuable and necessary to improve control of many weeds, including pigweed species, yellow nutsedge and morningglories.”

He said Valor SX is a good option and that applied pre-emergence “improved control of many broadleaf weeds, including pigweed and morningglory species. Valor SX must be applied to the soil surface prior to peanut emergence to avoid crop injury and should be applied with additional pre-emergence herbicides to improve control of other weeds, including grasses.”

He said pre-emergence materials also help control weeds that have developed resistance to other pre-emergence and postemergence herbicides. These include pigweed species resistant to ALS herbicides.

In 2010 herbicide trials, Valor SX showed “excellent control of many tough broadleaf weeds, including prickly sida, morningglory and pigweed. “But it offers very little grass control.” He said Valor plus Dual and Prowl provide excellent control of grasses and tough weed species.