EFFICACY AND COST-EFFECTIVENESS OF GRAIN PROTECTANTS APPLIED TO FARM-STORED WHEAT AT HARVEST AND LATER

Studies were conducted in 1989 and 1990 in wheat stored on farms in Kansas and Oklahoma to compare the recommended harvest-time application of grain protectant with a delayed application (4-6 wk after harvest) to a portion ofthe grain mass. In 1989, chlorpyrifos-methyl was applied by both methods to unaerated wheat. In 1990, the two application procedures were compared as part of an integrated program of insect pest management, and either chlorpyrifos-methyl or malathion was applied. Although the delayed application of chlorpyrifos-methyl appeared to reduce the number of insects captured in probe traps, and produced 98 +/- 1.1% mortality when bioassayed after 5 mo of storage, it did not significantly reduce insect density in samples from aerated lots and was not cost effective compared with no grain protectant. When malathion was used, neither the delayed application nor the application at harvest significantly reduced insect density in the stored wheat. Treatment with chlorpyrifos-methyl, either at harvest or later, significantly (P < 0.05) reduced insect density in grain samples in fall 1989 compared with the nontreated lots. In both trials, the application of grain protectant at harvest was associated with a greater overall cost index than no protectant treatment.