Grain aphids in New Brunswick. IV. Effects of malathion and 2,4-D amine on aphid populations and on yields of oats and barley

Abstract

Aphid populations on oats (Fundy and Stormont) and barley (Charlottetown 80) were studied in the field and yields of these grains examined under the different levels of aphid infestation resulting from applications of malathion and 2,4-D amine to the crop.Two species of aphid, Rhopalosiphum padi (L.) and Macrosiphum avenae (Fab.), occurred on the grains, and the greatest populations developed on barley. In all cases highest numbers were associated with applications of 2,4-D amine. Applications of this herbicide to similar aphids under laboratory conditions showed that the species differed in their responses as measured by reproduction and longevity.One malathion treatment, applied when aphids were dispersing into the field, reduced ensuing aphid numbers on oats by 29% and on barley by 64%. Yields of oats were increased by 47% and of barley 32% when malathion alone was used. When malathion and 2,4-D amine were applied together, aphid results and yield results were confusing.In all treatments, aphid populations collapsed abruptly once the grain panicle emerged, and in no case did aphids persist more than 10 weeks on either grain.