POTENTIAL OF NONCHEMICAL CONTROL STRATEGIES FOR REDUCTION OF SOIL INSECT DAMAGE IN SWEET-POTATO

This 2-year study was conducted to determine if soil insect damage cou ld be reduced in sweetpotato [Ipomoea batatas (L.) Lam] by treatment w ith an insecticide (fonofos) and/or a parasitic nematode (Steinernema carpocapsae Weiser), in conjunction with sweetpotato cultivars that di ffered in susceptibility to soil insect damage. Analysis of field data for the first year showed that the parasitic nematode provided signif icant damage protection of sweetpotato from wireworms (Conoderus spp.) ,Diabrotica sp., Systena sp., and sweetpotato flea beetle (Chaetocnema confinis Crotch), but not from grubs (Plectris aliena Chapin; Phyllop haga ephilida Say). In this same test, fonofos used alone provided pro tection against wireworm-Diabrotica-Systena (WDS complex) damage. In t he second test, the nematode did not provide soil insect protection fo r the WDS complex, but fonofos did reduce damage for these insects. Po or efficacy in the second test with the nematode probably was due to h igh rainfall, which saturated the soil. Resistant cultivars provided g ood protection for all three categories of damage. When used with the insect-susceptible check 'SC 1149-19', the nematode or fonofos treatme nts provided better control for all insect categories in the first tes t. In both years, much higher control of damage by all insect classes was achieved by the use of resistant cultivars in combination with the nematode and/or fonofos treatment (64% higher crop protection than th e susceptible check line). Chemical name used: O-ethyl-S-phenylethylph osphonodithioate [fonofos (Dyfonate 1OG)].