Aster Yellows Control in Head Lettuce and Carrots in Prince Edward Island1

Abstract

Weekly applications of DDT, 1 lb toxicant/acre, plus malathion, 1.25 lb, resulted in a significantly lower incidence of aster yellows in head lettuce, a virus disease transmitted in nature largely by the six-spotted leafhopper, Macrosteles fascifrons (Stål). Twice-weekly applications were more effective than weekly applications. Granular phorate applied to the soil with the seed at planting time at 1 lb toxicant/acre was as effective as either Di-Syston® (O,O-diethyl 5-[2- (ethylthio) ethyl] phosphorodithioate) or E.I. 43064 (2- (diethoxyphosphinothioylimino)-1-3-dithiolane) at 2 lb. Control of lettuce and carrot yellows with phorate was equal to that obtained with regular sprays of malathion or carbaryl. E.I. 47031 (2- (diethoxyphosphinylimine) 1-3-dithiolane) was not effective in reducing the incidence of lettuce yellows, although some control of carrot yellows was evident. Spraying barriers of sweet corn plants that completely surrounded lettuce and carrot plots, rather than the lettuce and carrots, was not effective in reducing the incidence of lettuce or carrot yellows.