A crop loss model and economic thresholds for the grain aphid, Sitobion avenae (F.), in winter wheat in southern Sweden

Sitobion avenae is one of the most harmful cereal aphids in western Europe and it damages winter wheat in southern Sweden. Field experiments with insecticides were carried out (1977-2002) in farmers' fields to evaluate the relationship between aphid density and crop yield and quality. A crop loss model is presented based on average annual yield loss in field experiments in high yielding varieties, 1995-2002, with low coefficients of variation. Aphid populations varied greatly between years and population peaks occurred at different crop stages. Less than 40% of the years since 1977 have been aphid years with more than 15 aphids/tiller on average. Peak values of aphids gave better regressions than aphid days. The economic injury level was found to be 7 aphids/tiller with a control cost of 300 SEK/ha and a wheat price of 1 SEK/kg. Volume weight and grain weight were only slightly affected by high aphid populations and the protein percentage was unaffected. The proposed crop loss model is a logistic curve: y = 0.38261n(x)-0.4108 (p < 0.001; r(2) = 0.9799; DF = 7) similar to a classic inverted S-shape with no damage under 4 aphids/tiller. The model shows rapidly increasing damage from 4 to 10 aphids/straw but much less damage/aphid at aphid levels from 15 to 40 aphids/tiller. Dynamic economic thresholds are proposed for different expected yield levels and different growth stages. Thus the economic threshold for high yielding wheat is 1 aphid/tiller at crop stage 59, 4 at crop stage 69 and 7 at crop stage 75. Economic injury levels and economic thresholds are important components of a cost-effective integrated pest management programme and are useful for decision-making in the application of pesticides. Understanding and appropriate use of economic decision levels in dealing with pests can increase profits and maintain environmental quality. (c) 2004 Elsevier Ltd. All rights reserved.