Effects of Insecticides Applied in the Field on Incidence of Aphid-borne Viruses in Cultivated Strawberry

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Abstract
Four pyrethroid insecticides and oxydemetonmethyl were evaluated in field spray application tests for ability to reduce the incidence of aphids and aphid-borne viruses in a field plot of Totem strawberry plants over a 2-yr period at Corvallis, OR [Orgeon, USA]. Ninety-four percent of the virus infection occurred during the second year of the test. Three pyrethroids (cypermethrin, permethrin, and fenalerate) and oxydemetonmethyl significantly reduced aphid-born virus incidence to 44-63% of the adjoining unsprayed plots at the end of the second growing season, whereas the pyrethroid bifenthrin gave a virus incidence that was not significantly different from that of the unsprayed treatment. Strawberry mild yellow-edge (SMYEV), a luteovirus, was present in 97% of the virus-infected strawberry plants and was the only virus detected in 88% of those plants. All insecticides caused a highly significant reduction of populations of the SMYEV vector aphid, Chaetosiphon fragaefolii, compared with the unsprayed plots in the second growing season. There was no significant associated between efficacy of insecticides in reducing aphid populations and virus incidence, however, suggesting that properties of these insecticides other than aphid kill may have influenced virus incidence.