Herbicide-resistant volunteer corn and the impact to weed management and insect resistance management.

摘要

Volunteer corn has reemerged as a problematic weed in corn:soybean rotational cropping systems. This reemergence and increasing prevalence of volunteer corn has been correlated to an increased adoption of herbicide-resistant (HR) corn hybrids and adoption of conservation tillage. Prior to the introduction of HR crops, the impacts of volunteer corn and available control options, had been discussed in the literature. Since the introduction of HR crops, control options, weed/crop competition, and other concerns (i.e. insect resistance management of Bt traits) have increased the amount of attention that volunteer corn is receiving. Preliminary data has suggested that the expression of transgenic volunteer corn Bt traits is highly variable, potentially exposing target insect pests to sub-lethal doses of toxin. The data also suggested that the high variability may be due to differences in soil fertility, especially nitrogen fertilizer applications. The objectives of our research were to quantify the competitive effects of volunteer corn growing in hybrid corn and soybean, and to quantify the expression of Bt toxins in volunteer corn growing in various nitrogen fertility environments; along with assessing the efficacy of the Bt trait Cry3Bb1 expressing in volunteer corn. Herbicide-resistant volunteer corn competing with soybean reduces soybean yield when it is not controlled and is growing at a density of 0.5 plants m-2. Herbicide-resistant volunteer corn competing with hybrid corn can reduce hybrid corn yield when growing at densities of 4 and 8 plants m-2, but if the volunteer corn produce grain, which can be harvested, the hybrid corn yield reduction is negated. The expression of Bt traits by volunteer corn is highly variable and is influenced by soil available nitrogen. As nitrogen rates are increased, the expression of Bt increases in the greenhouse. This result was not observed in the field though, although the high amount of Bt expression variability was observed. Overall, there is no difference between Bt expression in volunteer corn and hybrid corn, and the efficacy of the Bt toxin was no different between hybrid corn and volunteer corn. Our results demonstrate the importance of managing HR volunteer corn growing in corn and soybean fields to help protect crop yields and decrease the selection pressure of Bt traits on targeted insect pests.