EVALUATION OF FUNGICIDE SEED TREATMENTS FOR SHRUNKEN-2 (SUPERSWEET) SWEET CORN

Shrunken-2 (''supersweet'') sweet com hybrids suffer serious stand losses due to seed rot, damping-off, and seedling blight caused by various seedborne and soilborne pathogens. To identify an optimal fungicide seed treatment to improve shrunken-2 sweet com seedling stand in the field, we evaluated 30 treatments in 1989 and 11 in 1990 through a network of cooperators at 32 and 19 locations during 1989 and 1990, respectively. Treatment with a mixture of captan, thiram, metalaxyl, and benomyl (CTMB) was usually the best. In 1989 final stand with this mixture ranged from 13 to 86% (median 72%), compared to 1-72% (median 54%) for the untreated control. In 1990 treatment with CTMB produced stands of 8-91% (median 65%), compared to 0-89% (median 36%) for the control. Addition of other fungicides or insecticides to the CTMB mixture did not improve the final stand. Fungicides were identified that could substitute for certain components of the optimal mixture without loss of efficacy, but omission of any of the components usually resulted in reduced efficacy. The results indicate that an effective seed treatment for shrunken-2 sweet corn should include a broad-spectrum protectant fungicide such as thiram or captan-thiram, metalaxyl, and a systemic fungicide with activity against Penicillium and Fusarium, such as imazalil or a benzimidazole fungicide.