Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 9, 1996
Publication Date: N/A
Interpretive Summary: Barley yellow dwarf virus is the most widespread and economically damaging virus disease of cereal crops. The virus is responsible for yearly crop losses estimated at between 2 and 10 % of the total United States grain crop; however, regional losses may well exceed these estimates. There are no effective strategies to control this disease. The purpose of the research reported here was to examine the effects of a recently identified class of insecticides, the nitroguanidines, on the aphid vectors of BYDV. The insecticide imidacloprid is applied as a seed treatment, minimizing the amount of chemical needed, its environmental impact and the application costs. We determined that the chemical was effective at increasing the mortality of adult aphids feeding on plants grown from treated seed and effectively prevented the aphids from reproducing on the plants. A reduction in feeding by adults translated into fewer plants initially infected with BYDV. Fewer aphids developing in the crop meant a reduction in the spread of the virus within the crop. Imidacloprid was effective at significantly reducing aphid populations in winter wheat and spring oat crops in two years of study. The chemical was effective against all species tested when used at higher rates, but at lower rates the effectiveness varied depending on the species of aphid tested. Overall, imidacloprid, if registered for use on small grains, could become an important component of an integrated program aimed at controlling BYDV.
Technical Abstract: Imidacloprid is a seed-applied nitroguanidine insecticide that has both contact and long-lasting systemic properties. Its direct effects on cereal aphid populations and indirect effects on barley yellow dwarf luteovirus incidence were examined in laboratory and field studies. Adult longevity and fecundity of three aphid species caged on various aged oat or wheat plants grown from imidacloprid-treated seed was reduced, although the quantitative efficacy of the compound differed among aphid species. In 2 years of field trials using winter wheat & spring oat, aphid populations were significantly reduced in imidacloprid treated plots relative to un- treated controls. Although the number of alighting alate aphids did not significantly differe between imidacloprid treated or untreated plots, the number of apterous aphids remained significantly lower in the treated plots for a majority of the growing season. BYDV epidemics did not develop in spring oat in either of the 2 years. BYDV epidemics did develop in the fal in the emerging winter wheat crop. BYDV identified as the RMV serotype pre- dominated in both seasons & was effectively controlled in the imidacloprid plots during the 1991-92 season. In the 1992-93 season lower rates of imidaclporid were used & large numbers of Rhopalosiphum maidis, the princi- pal vector of RMV, immigrated into the young crop & similar levels of RMV were detected in treated & untreated plots. Later in the fall large numbers of R. padi migrated into the crop, many of which were carrying BYDV iden- tified as the PAV serotype. The final incidence of PAV was significantly higher in the untreated plots relative to the imidicloprid-treated plots. Imidacloprid offers several advantages both in terms of its application and long-lasting systemic activity.