Soil treatment with entomopathogenic fungi for corn rootworm (Diabrotica spp.) larval control

Abstract

Field trials were conducted in 1988 and 1989 to determine the efficacy of soil applications of the entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana against the southern corn rootworm (SCR), Diabrotica undecimpunctata, in corn. Dry mycelial particles were incorporated into the soil to a depth of 15 cm at rates of 9.3 and 0.93 g particles/m row at planting time. The concentration of fungus in soil increased during the first month postapplication and then decreased during the second month for both trials. One month after the application of fungus, the treated soil adjacent to corn plants was infested with 300-350 and 600-650 SCR eggs during 1988 and 1989, respectively. In 1988, the high treatment rate of M. anisopliae was equal to the uninfested control in preventing goose-necked plants and larval feeding on roots and in limiting adult emergence. The effectiveness of the high rate of M. anisopliae coincided with a stable soil concentration of the fungus of at least 2.7 x 105 CFU/cm3 soil during larval development. All other fungal treatments provided lesser degrees of plant protection and reduced adult emergence compared to the SCR-infested control. In 1989, the effectiveness of all fungal treatments was reduced compared to that in 1988. However, root damage ratings among plants in fungus-treated soil were significantly lower than those in the SCR-infested control.