Effects of Hypera nigrirostris, Hylastinus obscurus, and Sitona hispidula Populations on Red Clover in Southwestern Idaho1

Abstract

The lesser clover leaf weevil, Hypera nigrirostris (F.), was shown to have little effect on red clover seed yields in Idaho. The clover root borer, Hylastinus obscurus (Marsham), and the clover root curculio, Sitona hispidula (F.), lowered both the longevity and seed yields of red clover fields. A high population of these beetles usually resulted in unthrifty stands and in a lowering of expected yields. Populations of these 2 root-damaging species were rather closely correlated with the number of roots expressing disease symptoms. In the first seed crop year, spring-planted red clover fields generally had higher populations of all 3 beetles than fall-planted fields. Granular forms of heptachlor and dieldrin were used to manipulate the insect populations in this study.