Effects of Clover Root Curculio, Alfalfa Weevil (Coleoptera: Curculionidae), and Soil-Borne Fungi on Alfalfa Stand Density and Longevity in Kentucky

Abstract

Field studies were done in two stands of alfalfa, Medicago sativa L., from 1982 to 1984 to investigate the effects of clover root curculio, Sitona hispidulus (F.), alfalfa weevil, Hypera postica (Gyllenhal), and root rot fungi on alfalfa stand density and longevity. Alfalfa crown density in plots protected from these three pests, compared with plots with natural populations of one or more, was 47.9 and 43.2% higher in the 1981-seeded stand (after 27 mo) and the 1982-seeded stand (after 15 mo), respectively. Clover root curculio larvae appeared to reduce alfalfa stand density only during the first year of feeding (the year following spring seedling establishment). Plant mortality from clover root curculio occurred from June to August and was compounded by dry soil conditions and the presence of root rot fungi. Alfalfa mortality from alfalfa weevil defoliation occurred during the alfalfa overwintering period (stand seeded in 1981) and during the period from June to August (stand seeded in 1982). Alfalfa stand longevity was reduced by up to 2 yr by stresses from these pests. Based on regression equations, stand longevity in plots protected from these pests was about 5 yr from seeding.