St. Louis, MO — Tall. Common. Resistant. Tolerant. It doesn’t matter what descriptor you put in front of it, waterhemp is a problem for farmers from Texas to Maine, but it seems that Midwest farmers are bearing the brunt of this particular problem weed.

Midwest extension specialists are telling farmers to watch out for waterhemp in 2012. Southern Illinois University Professor of Weed Science Dr. Bryan Young estimates that 90 percent of Illinois acres from Bloomington to Decatur have waterhemp present.

“Waterhemp is a challenge for growers and has been for the last 20 plus years,” says Young. “Throw in the challenge of herbicide resistance and it’s no wonder that waterhemp has become public enemy number one for growers.”

While waterhemp is native to the U.S., it didn’t become a major agronomic problem until the 1980’s when reduced tillage systems and simplified weed management programs contributed to the problem that waterhemp is now.

“In Iowa, we have resistance to waterhemp in the triazine, ALS inhibitor, PPO inhibitor, glyphosate and HPPD inhibitor herbicides,” says Dr. Mike Owen, extension weed specialist and professor of agronomy at Iowa State University. “At this point, growers should presume resistance exists and plan their weed management programs accordingly.”

Weed Biology and Environment
Waterhemp seedlings are typically hairless with waxy and glossy leaves, with a native habitat of flood plains and other wet, low-lying areas. With this being said, the weed is also well adapted to conservation tillage and no-till.

The big challenge, however, is once waterhemp becomes established it has a growth rate 50 to 70 percent greater than other annual weed species. Combine that growth rate with the relative long germination of the plant and farmers have a problem on their hands.

“When allowed to compete with crops during the growing season, waterhemp can cause dramatic yield losses in both soybeans and corn,” says Dr. Rick Cole, weed management product manager at Monsanto Company. “Combine that with everything else we know about waterhemp and you can have a formidable – yet manageable – challenge for farmers.”

Managing Waterhemp
Researchers agree farmers should develop their weed management strategies as if all waterhemp is resistant to one or more herbicides and plan long-term management strategies.
“All herbicide weed management needs, including that for waterhemp, to be redundant,” says Owen. “Growers should focus on five years down the road not just on the flush in front of them or what they expect from the coming year.”

Beyond that, Owen provided some simple steps for managing waterhemp, and other resistant weed species.

· DO NOT use only one tactic or herbicide to control weeds.
· DO use tank-mixes of herbicides with different modes of action (MOAs) that will control the weeds of concern. Refer to the herbicide group number to determine if the herbicides have different MOAs.
· DO scout early and often. While you may not think weeds exist in the un-tilled fields, look closer. The weeds are there and they will cost you money if you do not manage them prior to, or IMMEDIATELY after, planting.
· DO use a soil-applied residual herbicide on all acres regardless of crop or trait.
· DO know what herbicides you are planning to use, what they control, replant restrictions and if there is significant potential for crop injury.

Cole agrees, “These steps are critical for farmers who are managing for waterhemp. It is with these recommendations in mind that we have created the Roundup Ready PLUS platform for farmers.”