Field experiments on the chemical control of blackcurrant reversion virus and its gall-mite vector (Phytoptus ribis Nal.)

Healthy blackcurrant bushes and others infected with reversion virus were exposed equally to infestation by the gall-mite vector (Phytoptus ribis Nal.) spreading from unsprayed sources planted nearby. Four applications of 1·0% lime sulphur at fortnightly intervals during the dispersal period were less effective than 0·05% endosulfan in preventing the infestation of healthy bushes, whereas endrin at 0·04% gave almost complete control. All spray treatments were much less effective when applied to the virus-infected bushes, although endosulfan remained superior to lime sulphur and inferior to endrin. Infected bushes sprayed with lime sulphur developed more galls than unsprayed healthy bushes. In another experiment, four applications of endrin or lime sulphur decreased the spread of mites and reversion virus from infested bushes to adjacent sprayed and unsprayed bushes. Lime sulphur was much less effective than endrin in preventing infestation with mites, but more effective in decreasing the incidence of virus. These results are discussed in relation to commercial spray programmes and to the design of experiments on the effectiveness and mode of action of spray materials against mites and virus.