A recently completed bioassay indicates concerns for management of corn earworm, particularly in sweet corn. The bioassay was conducted with larvae collected from non-treated sweet corn grown on the UGA Tifton Campus. Early instar (late 2nd to early 3rd instar) corn earworm larvae were collected and exposed to selected insecticides in a maximum dose leaf dip bioassay. Insecticides tested were those labeled for corn earworm control during ear formation in sweet corn. Insecticides and rates tested included Warrior (1.92 fl oz), Coragen eVo (2.5 fl oz), Lannate (1.5 pts), and Radiant (6 fl oz). The 1X rate was mixed as if spraying at 100 gpa and included a surfactant to insure coverage of the dipped leaves. Non-treated soybean leaves were used in the bioassay. Leaves were allowed to dry and then placed into individual diet cups and a single larva added to each. Mortality was checked 3 days after initial exposure.
Results (shown below) indicate high survival in both the Warrior and Coragen treatments (rates tested would be expected to cause near 100 % mortality). Fortunately, both Lannate and Radiant continue to provide good control. The resistance is of particular concern for sweet corn producers as multiple applications are required for control of corn earworm (versus one or two applications in other crops) and alternative chemistries are also limited in sweet corn.
