The first confirmed case of weeds resistant to HPPD-inhibiting herbicides has been found in waterhemp in Illinois, according to University of Illinois weed scientists.

Foliar-applied HPPD inhibitors — alone or tank-mixed with atrazine — provided poor control of this waterhemp population, says Aaron Hager, University of Illinois weed specialist. Several active ingredients in this herbicide family — including tembotrione, topramezone and mesotrione — are commercially available as individual products like Callisto, Laudis and Impact or as components of pre-mixtures.

“This particular field was used for seed-corn production and for 7 consecutive years, there was over-reliance on certain post-emergence HPPD-inhibitor herbicides to control key weeds,” says Chuck Foresman, Syngenta’s manager of weed-resistance strategies. “Hybrid seed-corn production systems often preclude the use of important broad-spectrum herbicides like glufosinate or glyphosate. The lack of diversity in both herbicide modes of action and crop rotation in this field led to the development of resistant waterhemp.”

Syngenta says pre-emergence applications of HPPD inhibitors Lumax and Lexar (containing mesotrione, S-metolachlor and atrazine) provided effective control of this waterhemp population. Syngenta says its field tests also indicate that the following products applied post-emergence controlled the waterhemp population: PPO inhibiting herbicides; certain glufosinate-and-auxin-containing herbicides; and glyphosate.

Since 1997, waterhemp resistant to ALS-inhibiting herbicides, triazines, PPO inhibitors and glyphosate have been confirmed in Illinois.

“While resistance to any one herbicide family can introduce significant management challenges, biotypes with resistance to more than one herbicide family are becomingly increasingly common,” Hager says.

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