Effects of Bifenthrin on Mycorrhizal Colonization and Growth of Corn

The insecticide bifenthrin is a synthetic pyrethroid required by regulation for the production of nursery crops to suppress the red imported fire ant (Solenopsis invicta) in Orange and Riverside counties in California. We conducted a greenhouse experiment to analyze the effects of different rates of bifenthrin on the growth and mycorrhizal colonization of 'Silver Queen' corn (Zea mays) inoculated with VAM 80 (R), a mycorrhizal inoculum with spores, hyphae, and root pieces colonized by Glomus spp., used to inoculate California native plants in containers. Corn was used because it is the standard indicator plant used for mycorrhizal inoculum potential assays and it is a good host for arbuscular mycorrhizal fungi propagation. The application of bifenthrin had no detrimental effects on mycorrhizal colonization of corn. There were no significant differences in the root length colonized by arbuscules, vesicles, or in the total percentage of mycorrhizal colonization obtained in the plants grown with the different bifenthrin rates 6 weeks after transplanting. However, there were significant interactions on the effects of bifenthrin and mycorrhizal colonization on plant growth. The addition of 12, 15, and 25 ppm of bifenthrin reduced corn biomass of nonmycorrhizal plants, but had no effect on the growth of mycorrhizal plants. There were no significant differences between the mycorrhizal and nonmycorrhizal plants grown with 0, 10, and 12 ppm of bifenthrin. In contrast, inoculation with VAM 80 (R) increased the shoot dry weight of plants grown with 15 and 25 ppm of bifenthrin. This study showed that mycorrhizal colonization can be helpful to overcome some of the negative effects of bifenthrin on the growth of corn.