Weed waterhemp now resistant to five herbicide groups

A common weed for U.S. corn and bean farmers, and also present in Ontario, just got even more troublesome.

Waterhemp in Illinois was already known to be resistant to four classes of herbicides — triazine, PPO inhibitors, glyphosate and ALS inhibitors. AgWeb is now reporting the the first documented case of resistance to post-emergence HPPD inhibitor herbicides (Group 27). Products with this group include Laudis, Impact and Callisto.

A waterhemp population in a central Illinois seed corn production field has been shown to withstand foliar applications of the popular herbicide.

University of Illinois weed scientist Aaron Hager said anecdotal reports from the field in 2009 indicated there might be a problem, which was reinforced by greenhouse tests.

"Field research conducted in 2010 has confirmed the greenhouse results," Hager says int he AgWeb article. "Foliar-applied HPPD inhibitors, alone or tank-mixed with atrazine, provided poor control of this waterhemp population."

Common waterhemp is a member of the pigweed or amaranth family. Like corn and sorghum, it is a C4 plant that is very efficient at fixing carbon. Its capable of producing 500,000 seeds per plant that tend to germinate throughout the summer.