THE CONTROL OF POTATO VIRUS DISEASES BY INSECTICIDES

Replicated trials were carried out in the years 1950, 1951, 1953 and 1954 to see if the spread of leaf-roll virus and virus Y in potato crops could be reduced by applying insecticides. The crops were disease-free, except for small numbers of deliberately introduced infected plants, and were sprayed at intervals of 10 or 14 days, according to the stage of growth of the plants, with a tractor-mounted spraying machine at 1OO gal./acre/application. Disease spread was estimated by growing tubers taken from the five plants on either side of each infector. DDT emulsion, DDT suspension, endrin, schradan, mipafox, malathion, parathion and Systox prevented the spread of leaf-roll virus and decreased the spread of virus Y, although DDT emulsion was the only insecticide used in all the trials. Dieldrin and toxaphene were ineffective. When virus control was successful, aphid control (estimated by counting apterae in the crops) was good.