Resistance to HPPD-inhibiting herbicides in a population of waterhemp (Amaranthus tuberculatus) from Illinois, United States.

Background: A population of waterhemp in a seed maize production field in central Illinois, United States, was not adequately controlled after post-emergence applications of herbicides that inhibit 4-hydroxyphenylpyruvate dioxygenase (HPPD).

Results: Progeny from the field population survived following treatment with mesotrione, tembotrione or topramezone applied to the foliage either alone or in combination with atrazine in greenhouse experiments. Dose-response experiments indicated that the level of resistance to the HPPD inhibitor mesotrione is at least tenfold relative to sensitive biotypes.

Insecticide and Insecticide Metabolite Interactions with Cytochrome P450 Mediated Activities in Maize.

In vitro assays were used to determine if organophosphate, carbamate, and synthetic pyrethroid insecticides affected the cytochrome P450 monooxygenase (P450) catalyzed hydroxylation of nicosulfuron, bentazon, cinnamic acid, or lauric acid in maize microsomes. All P450 activities were inhibited approximately 50% by carbaryl, and none were inhibited by permethrin. Hydroxylations of nicosulfuron, bentazon, lauric acid, and cinnamic acid were inhibited by malathion 83, 92, 38, and 0%, respectively.