Source: Bob Hartzler, Department of Agronomy, Iowa State University

Waterhemp caused significant economic losses for many Iowa growers during the mid-1990s. With the introduction of new technologies, primarily Roundup Ready soybeans, most farmers have minimized the economic impact of waterhemp in corn and soybean production. However, the selection of herbicide-resistant waterhemp biotypes threatens to return us to an era where uncontrolled waterhemp causes significant yield losses across the Corn Belt.

The first appearance of resistance to the HPPD inhibitors was reported in 2009 in waterhemp found in two fields in Iowa and Illinois. Several factors contributed to this appearance.

The two fields where HPPD resistance evolved are approximately 140 miles apart, but they have several similarities in management practices. The Illinois field was maintained in continuous corn since at least 2003, whereas the Iowa field was a corn-soybean rotation. However, both fields were used for seed corn production during the period of HPPD use. 

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