No new herbicide active ingredients are currently available for the 2011 growing season, and University of Illinois Extension weed specialist Aaron Hager said he expects this “drought” of no commercialization of herbicides with unique sites of action to continue into the foreseeable future.

“With no new sites of herbicide action being commercialized, it’s likely that we will see increased challenges caused by herbicide-resistant weed biotypes and populations this year,” Hager said. “However, making accurate predictions about the types of challenges weeds might present during the 2011 growing season is a bit tenuous.”

Last fall’s corn harvest was much more timely and efficient than what many farmers experienced in 2009, Hager said. One consequence of 2009’s challenging harvest was the abundance of volunteer corn in 2010. Densities of volunteer corn were quite impressive and required careful attention when selecting the appropriate control option.

“We expect that volunteer corn will, once again, be a weed management consideration in 2011,” he added. “But we expect volunteer corn densities to be much lower than what we experienced in 2010.”

Hager believes more acres of the 2011 soybean crop will be treated with a soil-residual herbicide than were treated in 2010. This will help alleviate many challenges posed by total postemergence weed control systems, including the unpredictability of being able to make timely POST herbicide applications before weed interference reduces crop yield potential.

“The high market prices for soybean, coupled with the increasing occurrence of herbicide-resistant weeds, suggest that soil-residual herbicides are likely to become staples of more integrated weed management systems,” he said. “Keep in mind, however, that simply applying the herbicide to the soil doesn’t always guarantee its optimal performance.”

Herbicide-resistant weeds are poised to become an even larger weed management challenge this year. Results of recent surveys indicate that glyphosate- and PPO-resistant waterhemp populations are present in many Illinois counties, and that glyphosate-resistant horseweed/marestail is very common across most of the southern third of the state.

In 2010, Hager documented a McLean County waterhemp population that was resistant to HPPD inhibitors, increasing the number to five herbicide site-of-action families to which Illinois waterhemp has evolved resistance.
“We expect that waterhemp biotypes resistant to multiple herbicide families will become even more common,” he said. “There are also concerns with populations of giant ragweed and palmer amaranth in southern Illinois that have not been controlled by glyphosate.”

For more information on changes in herbicide options available to Illinois weed control practitioners, read the March 24 edition of The Bulletin at http://bulletin.ipm.illinois.edu/.