APHID (HOMOPTERA, APHIDIDAE) MANAGEMENT IN ALFALFA BY SPRING GRAZING WITH CATTLE

The effect of continuous, intensive grazing by cattle on aphid populat ions was examined in the first growth cycle of 'Alfagraze' and 'Apollo ' alfalfa which are tolerant and not tolerant to grazing, respectively , Populations were almost entirely pea aphid, Acyrthosiphon pisum (Har ris). The effect of grazing on aphid populations was examined in small plot exclusion studies in 1991 and 1992, and the effects of grazing a nd use of an early insecticide application with less than or equal to 7 day grazing restriction were examined in large plot exclusion trials in 1993 and 1994. Grazing reduced aphid populations by 66% to 90% whe n numbers exceeded similar to 1 aphid per stem. Populations were not s ignificantly reduced by grazing when numbers did not exceed 1 per stem . Permethrin reduced aphid numbers for up to 7 wks and was more effect ive than carbofuran. Effects of grazing were similar regardless of ins ecticide usage. Coccinellid beetle populations in 1993 and 1994 were c omposed of Coccinella septempunctata L., Harmonia axyridis (Pallas), a nd Coleomegilla maculata DeGeer. Coccinellid numbers were much lower i n grazed than ungrazed plots when aphid numbers were reduced by grazin g in 1993, but were not greatly affected by grazing in 1994 when aphid numbers were low. Coccinellid numbers paralleled trends in aphid numb ers. Continuous, intensive grazing or the early application of an inse cticide at a low rate followed by grazing were effective approaches fo r suppressing pea aphid in alfalfa.