Herbicide resistant weeds increasing in Iowa, around country
By Jean Caspers-Simmet
Date Modified: 06/04/2012 2:22 PM
INDEPENDENCE, Iowa —Waterhemp epitomizes the problem of herbicide resistant weeds, said Mike Owen, Extension weed specialist.
Waterhemp has evolved resistance to six herbicide classes, Owen said during a recent meeting in Independence.
Waterhemp has prolific seed production and genetic flexibility. Resistance is due to rare mutations that result in a mechanism that allows a plant to survive a herbicide that previously was effective. Because waterhemp can produce hundreds of thousands of seeds, the probability of a mutation occurring that provides resistance to a herbicide increases.
"The biotypes with multiple resistances are very common, therefore greatly limiting our herbicide options," Owen said.
Resistance in common waterhemp has increased significantly for populations with evolved resistance to glyphosate, and resistance to HPPD herbicides has been identified in several Iowa locations.
"Glyphosate resistance in Iowa common waterhemp has increased dramatically in 2011 and is widely distributed around the state," Owen said. "Populations with resistance to PPO inhibitors are also becoming more common. Nebraska recently identified waterhemp with resistance to 2,4-D. Herbicide resistant giant ragweed and marestail are also increasing in Iowa."
With 210 million acres of Roundup Ready technology crops planted globally, and 130 million to 150 million acres in the United States every year with much of it sprayed two or more times with glyphosate, the likelihood of selecting the resistance trait is pretty good, Owen said.
Owen said it's likely that some Iowa farmers will face serious economic consequences due to herbicide resistance similar to what cotton farmers face in the Southeast.
"But with thoughtful use of herbicides and other management strategies, economically viable weed management programs can be developed and the problems associated with herbicide resistance can be minimized," Owen said.
Don't expect a silver bullet.
"It's unlikely that new herbicide mechanisms of action will be introduced in the foreseeable future," Owen said.
The development of new genetically engineered crop traits with regard to dicamba-tolerant soybeans and DHT soybeans and corn are not the silver bullet some suggest, he said.
"There are concerns about the movement of the herbicides used in these genetically engineered crops to sensitive crops such as grapes and also whether or not the use of the systems will result in new resistant weed biotypes," Owen said. "There are no new widgets in the near term."