Validation of models that predict the peak density of grain aphid (Sitobion avenue) and yield loss in winter wheat

Aphid counts and yield results from a three-year field trial of the effectiveness of insecticides applied at various growth stages of winter wheat, were used to test the accuracy of the predictions of the Entwistle and Dixon (1986, 1987) models for forecasting aphid damage and population growth. In general, the peak aphid populations of Sitobion avenae and damage were not accurately predicted but the spray recommendations, which would have resulted from the predictions, would have been correct in each of the three years; one outbreak and two non-outbreak years. In particular the effectiveness of early spraying was over-estimated because the persistence of the effect of insecticides was over-estimated. It is recommended that further work be done on the rate of development of aphid populations following application of insecticides.