Woolly aphid of apple, Eriosoma lanigerum (Hsm.), and its control in Southern Rhodesia

Abstract

In insecticide trials in Southern Rhodesia against the woolly apple aphid, Eriosoma lanigerum (Hsm.), using methyl-demeton (0·078 and 0·052 per cent. active ingredient), dimethoate (0·0625 and 0·0417 per cent. active ingredient), diazinon (0·0625 per cent. active ingredient) and malathion (0·1041 per cent. active ingredient) as foliar sprays, all insecticides gave good control of infestations above ground, but methyl-demeton and diazinon gave the best control, and treatments were followed by slower rates of repopulation.Injecting the lower part of the trunks of trees 25 to 30 years old with ½ fluid ounce of a concentrate of a systemic insecticide, 50 per cent. methyl-demeton or 40 per cent. dimethoate, at a single point gave excellent control where that part of the sap stream supplying the aphid colonies was intercepted. By injecting with a spiral of small holes around the trunk using ½ fl. oz. 50 per cent. methyl-demeton, control of all aphids on the tree could generally be achieved.Good control of subterranean aphid colonies on 15-year-old trees was achieved by the application to the soil of 4 gal. per tree of a fluid containing 100 cc. of a concentrate containing 75 per cent. of V-C 13 (O,O-diethyl O-2,4-dichlorophenyl phosphorothioate) diluted with water.Biological control of E. lanigerum in Southern Rhodesia by the Hymenopterous parasite Aphelinus mali (Hald.), which was introduced in 1961, shows great promise.