REDUCTION OF WIREWORM (COLEOPTERA, ELATERIDAE) DAMAGE IN SWEET-POTATO WITH INSECTICIDES APPLIED BY CHEMIGATION

Chemigation of insecticides was compared with soil incorporation of granular insecticides to reduce feeding damage of wireworm, Conoderus spp., to sweet potatoes. In 1988, emulsifiable (EC) and oil (EC plus nonemulsifiable oil) formulations of chlorpyrifos chemigated at two water volumes were compared with soil-incorporated chlorpyrifos granules at planting. In 1989 and 1990 EC and oil formulations of chlorpyrifos, chemigated at planting, were followed at root enlargement by chemigated EC and oil formulations of chlorpyrifos, diazinon, ethoprop, or fonofos. These treatments were compared with soil-incorporated chlorpyrifos granules applied at planting followed at root enlargement by soil-incorporated ethoprop or diazinon granules. During all years, there were no significant differences among formulations in total wireworm feeding damage and all treatments resulted in significant reduction of feeding damage compared with the nontreated check. In 1988, chlorpyrifos chemigated in 63.5 kliter/ha of water resulted in significantly less wireworm damage than when applied in 25.4 kliter/ha of water and was as effective as the soil-incorporated granules. In 1989, plots chemigated both at planting and at root enlargement had significantly less wireworm damage than plots chemigated only at planting. In 1990, when the wireworm population was high, granular chlorpyrifos applied only at planting was more effective than EC of oil formulations of chlorpyrifos chemigated only at planting but was not significantly different from either formulation of chlorpyrifos chemigated at planting followed by EC or oil formulations of ethoprop or diazinon chemigated at root enlargement. Chemigation of insecticides to the soil to control wireworm damage of sweet potato can be an effective, cost-saving alternative to mechanical incorporation of insecticide. Savings include reduction of application costs and less damage to the crop caused by mechanical incorporation of insecticide.