Glyphosate-Resistant Weeds Require Attention

Whether you have experienced any weed resistance to glyphosate herbicide treatments or not, weed specialists suggest soybean farmers consider spending a little more time on management in 2010.  Both marestail and waterhemp require more attention to keep them under control.

“We are already seeing a shift in practices, including more use of 2,4-D ahead of soybean planting to control resistant marestail, as well as more consideration for soil-applied herbicides to handle glyphosate-resistant waterhemp,” says Bryan Young, weed scientist at Southern Illinois University-Carbondale (SIUC).  “If you want to manage for higher yields, you must do a better job managing glyphosate-resistant weeds.  Weed management will interact with other practices for increasing crop yields, such as fungicide and insecticide foliar sprays and seed treatments.”

Young and fellow weed specialists Aaron Hager and Robert Bellm from the University of Illinois helped develop a new, “Stop Glyphosate Resistance” brochure sponsored by SIUC, the University of Illinois, the National Soybean Research Laboratory (NSRL) and the Illinois Soybean Association (ISA).  The brochure contains step-by-step details about how to control both glyphosate-resistant marestail and waterhemp in Illinois soybeans.  In addition, the brochure answers questions on how and why the control procedures were established.

“Education on glyphosate stewardship and management of problematic weed species is a significant part of the ISA Weed Managed Research Area (MRA).  Other research projects include development of weed control strategies for problematic weeds, increasing knowledge of target weeds, especially glyphosate-resistant biotypes, and the impact of agronomic practices on weed management,” Young says.  “More specifically, we are investigating tank mix partners with glyphosate, bioherbicide controls and such practices as soybean seeding rate and plant populations.”

For the 2010 season, Young recommends Illinois soybean farmers stick with the basics for effective weed control and scouting.  He advises always starting with a clean seedbed, although he warns that weather can play a role in seedbed preparation.  For no-tillers, that means using an effective burndown herbicide program.  For other tillage systems, make sure appropriate tillage is performed to kill all existing plants.  Some tillage tools do not completely remove all weeds in a single pass.

“Once you are in season and you have made a glyphosate application, monitor it for efficacy.  If you see any inconsistency in your weed control, you may need to alter your weed management strategy for the next year,” Young says.  “But chances are you are going to have to do something different, like try a soil-applied treatment.  More farmers may have to do this to achieve effective control.”

Finally, Young encourages farmers to make sure foliar herbicide applications are timely, whether in conventional production settings, Roundup Ready or Liberty Link programs.  Weeds should be treated at labeled rates and labeled heights to get the best control.

“We do want farmers to watch giant ragweed closely this season.  The weed has not been confirmed as glyphosate resistant in Illinois, but observations show giant ragweed is not being killed completely with glyphosate.  Report any suspicious glyphosate non-performance to local weed specialists,” he says.

-Funded through the Soybean Checkoff