Economic Injury Levels and Economic Thresholds for Cereal Aphids (Homoptera: Aphididae) on Spring-planted Wheat

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Abstract
Foliar insecticide treatments were applied at various stages of plant growth to control natural infestations of two cereal aphids, the English grain aphid, Sitobion avenae (F.), and the rose-grass aphid, Metopolophium dirhodum (Walker), in field plots of spring wheat. Yield increases of 2.7 t/ha (36.5%) and 1.2 t/ha (29.3%) were obtained when sprays were applied at flowering in 1984 and 1985, respectively. Lower but significant yield increases were also obtained when sprays were applied at the milky ripe and early dough stages. Depending on the cost of chemical treatment and price received per kilogram of wheat, the economic injury level was calculated to be 15 and 10 aphids per tiller in 1984 and 1985, respectively. Based on the plant growth stage and the rate of aphid population growth, economic thresholds were calculated to be 2–4 aphids per tiller at flowering, 6–10 aphids per tiller up to the milky ripe stage, and 10 or more aphids per tiller from the milky ripe to medium-dough stage. After the medium-dough stage, treatment cannot be justified.

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