Determination of economic injury levels and economic thresholds of viruliferous cereal aphids on a winter and a spring wheat
Abstract
The effect of viruliferous Rhopalosiphum padi (L.) and Sitobion avenae (F.) on plant height, grain yield and grain yield components, namely: number of tillers per plant, number of kernels per head and 1000-kernel weight, were determined on the winter wheat cultivar Abe and the spring wheat cultivar Marshall. Experimental plots, each consisting of a 1.3 m row of ca. 30 wheat plants were established in a randomized complete block design of three blocks and eight treatments. During 1985-86, each aphid species, wheat cultivar, growth stage, four infestation levels (0, 5, 50 and 100 aphids/tiller) and two durations of infestation (one and two weeks) were evaluated. During 1986-87, the infestation levels were 0, 5, 25, and 50 aphids/tiller and the infestation periods were one and seven days. These controlled infestations were repeated at the seedling (stage 1), flowering (stage 10.5.1) and at the ripening (stage 11.1) growth stages (Feekes scale). All plots were caged in screen enclosures. At crop maturity plant height and four yield components were measured for each plot. Infestations at seedling stage caused the greatest yield losses. These losses were mostly due to a reduction in number of tillers/plant. The lowest yield losses resulted from infestations at the ripening stage, and were due mainly to a reduction in the 1000-kernel weight. Infestations at the flowering stage caused yield losses, mainly by reducing the number of kernels per head. In both years and in both cultivars, S. avenae caused more damage than R. padi at the flowering and ripening stages. During 1985-86, Economic injury levels (EILs) of R. padi on Abe averaged 5, 10, and 20 aphids/tiller for seedling, flowering and ripening stages, respectively. Economic thresholds (ETs) averaged 4, 10, and 19 aphids/tiller respectively. EILs of S. avenae on Abe averaged 5, 7, and 9 aphids/tiller and (ETs) averaged 4, 7, and 8 aphids/tiller. On Marshall, EILs of R. padi averaged 5, 10, and 13 aphids, and ETs averaged 4, 9, and 13 aphids/tiller. EILs of S. avenae averaged 5, 7, and 11 aphids/tiller, and its ETs averaged 4, 6, and 11 aphids/tiller. During 1986-87, both EILs and ETs were in general lower than those of the first year.
Degree
Ph.D.
Advisors
Foster, Purdue University.
Subject Area
Entomology|Agricultural economics
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