A COMPARISON OF HIGH AND LOW VOLUME SPRAYS FOR CONTROL OF THE BEAN APHID APHIS FABAE SCOP. ON FIELD BEANS

Insecticides were sprayed in different amounts of water to control Aphis fabae Scop. attacking spring-sown field beans. The single application of each insecticide was timed to coincide with the end of aphid migration from the winter host to the crop. A tractor-mounted row-crop hydraulic sprayer was used. In one experiment seven different insecticide sprays were compared at high volume ( in 140 gal. of water per acre); the most effective were nicotine at 22.4 oz. of active constituent per acre, demeton at 5.6 oz. and demeton-methyl at 11.2 oz. A further comparison was made of five insecticides for each of which a selected dose of active ingredient was applied in 60 gal. ( medium volume) and in 10 gal. of water per acre ( low volume). The amount of insecticide retained on the plant following the low-volume application was not less than that from the medium-volume spray; the efficiency of A. fabae control was not affected by the volume sprayed except with malathion which did better at the medium volume. The systemic insecticides demeton-methyl at 6 oz. of active constituents per acre, the related compound 4741 at 3 oz. and fluoroacetamide at 3 oz. stopped the aphid numbers from rising above a peak of eight per plant compared with 230 per plant for malathion ( low volume) at 12 oz. 2400 per plant for lindane at 6 oz. and 3550 per plant for check treatments sprayed with wetter only. Grain yields ranged from around 4 cwt. per acre on check treatments to around 27 cwt. per acre on plots sprayed once with the systemic insecticides. There was a curvilinear relationship between grain yield and log number of A. fabae per plant.