Yield losses of faba bean due to aphid attack.
To determine the correct time to apply a single insecticidal spray to control Aphis craccivora on faba beans (Vicia faba) in Middle Egypt, beans were sown in November 1982 and population build-up and plant damage were monitored weekly. Plots receiving 4 fortnightly sprays of dimethoate between 26 February and 9 April 1983 remained aphid-free throughout the season. A single application of dimethoate on 26 March (when there were many scattered colonies of nymphs on the plants) reduced the aphid populations but did not prevent heavy to very heavy damage to the leaves. In plots artificially infested with A. craccivora in February and not treated with insecticide, heavy populations built up by late March and damage was heavy to very heavy throughout March and April. Untreated plots not artificially infested had few to many scattered colonies of aphids in March, but numbers declined in April; the plants suffered slight to heavy damage. The numbers of pods per plant and the mean weight in grammes of the seeds from 10 plants were 17.2 and 499.5, respectively, for 4 treatments, 13.4 and 333.6 for a single treatment on 26 March, 9.6 and 275.8 for artificially infested plants and 11.6 and 298 for the untreated control plants. The occurrence of many scattered colonies of nymphs resulted in severe damage; treatment just before the second half of March is recommended to prevent yield losses.