EFFECTS OF STRAW MULCH, SPENT MUSHROOM COMPOST, AND FUMIGATION ON THEDENSITY OF COLORADO POTATO BEETLES (COLEOPTERA, CHRYSOMELIDAE) IN POTATOES

Colorado potato beetle, Leptinotarsa decemlineata (Say), population tr ends were monitored in potatoes under different pest management and cu ltural regimes. Four cultural practices (straw mulch, spent mushroom c ompost, both mulch and compost, and conventional practices without mul ch or compost) were used as subplots within main plots representing 3 pest management practices. In 1992, beetles were managed by hand remov al until July, and the 3 treatments were removal without soil fumigati on, no removal without fumigation, and no removal with fumigation. In 1993 and 1994, beetles were managed by use of insecticides, and the 3 treatments were insecticides with soil fumigation, insecticides withou t fumigation, and no insecticides with fumigation. Straw mulch reduced the density per square meter of adults and large larvae in plots with out beetle management in 1992 and 1994, and the density of adults in i nsecticide-treated plots in 1993. Defoliation was lower in mulched sub plots without beetle management in 1992 and 1994, and leaf area (1992) or ground cover (1994) was increased in these treatments, but yield w as not affected. Compost increased leaf area and yield in 1992, and in creased the density of adults and egg masses in that year, but general ly had minor effects on beetle density and varying effects on yield. F umigation significantly decreased yield in 1992 and 1994, and it had n o effect on yield in 1993. Any benefits of fumigation in mitigating di sease were offset by the earlier peak in density of large larvae in 19 92, and the greater density of adults in 1993 and 1994 in fumigated pl ots compared with plots without fumigation.