EXPERIMENTS ON THE CONTROL OF BEET YELLOWS VIRUS IN SUGAR-BEET SEED CROPS BY INSECTICIDAL SPRAYS

Field experiments made in eastern England between 1943 and 1951 showed that Myzus persicae lived on the stecklings throughout some winters, and that most plants with yellows in transplanted seed crops were from infections that occurred in the steckling bed. A larger proportion of stecklings sown at the end of July or in early August became infected than of those sown about a month later. The incidence of yellows was reduced by nicotine sprays which cleared the stecklings of aphids after autumn migrations had ceased, thus preventing spread of the disease during the winter. A greater reduction was obtained with persistent and systemic organo-phosphorous insecticides; in one experiment three applications of E 605 reduced incidence to one-ninth that in unsprayed plots. However, in years when stecklings were exposed to large migrations of aphids, even plots sprayed three times had 78% of the plants with yellows. Although spraying often greatly reduces the incidence of yellows, it is unlikely to give adequate control in years and districts in which many viruliferous aphids move in the autumn. Spraying in September and October was usually more effective than in August.