Insect distribution in a spring pea-winter wheat-spring barley crop rotation system

The effects of tillage method (conventional or conservative) and weed manag ement level (recommended or minimum) on insect distribution in a wheat (Tri ticum aestivum L.), barley (Hordeum vulgare L.), and pea (Pisum sativum L.) rotation were studied. Aphids were the major insect species on winter whea t and spring barley, but were not of economic importance. Beneficial specie s impacted aphid population levels by maintaining their numbers below econo mic thresholds. Tillage method and weed management level had limited impact on aphid and beneficial insect populations. Pea leaf weevil (Sitonia linea tus [L.]) and pea weevil (Bruchus pisorum [L.]) populations reached economi c injury levels in 1992; two insecticide applications were needed. Pea leaf weevil populations did not reach economic levels in 1993; however, pea wee vil populations reached an economic level at flowering stage and an insecti cide was applied. Pea leaf weevil populations were higher in conventional t illage plots compared with conservation tillage plots. Early-season insecti cide applications suppressed beneficial insects in the pea plots.