Reduction in Yield and Quality of Leaf and Stem Components of Alfalfa Forage Due to Damage by Larvae of Hypera postica (Coleoptera: Curculionidae)

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Abstract
Variable rates of carbofuran were used to obtain a gradation of larva population densities of the alfalfa weevil, Hypera postica (Gyllenhal), in nonirrigated ‘Oklahoma Common’ alfalfa, Medicago sativa L. Damaged and undamaged alfalfa stems were collected according to a 10-point defoliation rating scale. Leaf and stem components were separated and analyzed for yield and crude protein content. Regression analyses were conducted to correlate alfalfa performance parameters with levels of weevil damage. As damage due to weevil larvae increased, yield reductions in both leaf and stem components were readily apparent. Crude protein content of leaves was reduced as a result of larva feeding. Protein levels in stems were highest early in vegetative growth and declined thereafter. No consistent trends in crude protein content of total herbage could be demonstrated due to high protein levels in stems throughout vegetative growth which masked effects of losses of high protein leaf tissues. There were no definite trends in percent of in vitro dry matter digestibility (IVDMD) of leaves related to weevil damage. Lowest percentages of crude protein and IVDMD in stems and total herbage resulted when plants reached full bloom before being harvested.