Control of aphids in glasshouses with the fungus, Verticillium lecanii

SUMMARY In small glasshouses, aqueous sprays of spores of the entomopathogenic fungus, Verticillium lecanii , eliminated small populations of the aphid Brachycaudus helichrysi in the vegetative tips of chrysanthemum plants but not when they were in an exposed position on mature flower buds. Control of the chrysanthemum aphid, Macrosiphoniella sanborni , was however variable and usually commercially unsatisfactory. In contrast, in both small and large glasshouses, sparse populations of the major aphid pest Myzus persicae were successfully and consistently controlled, sometimes spectacularly. The inherent susceptibilities of these aphid species, measured by laboratory bioassay, did not account for the differences in control observed in the glasshouse. It is thought that a combination of species‐characteristic feeding site preferences on the exposed parts of plants, where microclimate humidity was probably low, and relative immobility of M. sanborni and B. helichrysi explain why these aphids were less well‐controlled than My. persicae . However, it should be possible to control satisfactorily all aphid species in large commercial glasshouses where humidity might be higher than in the small experimental glasshouses. A single spray was sufficient to introduce infection that controlled aphids for the duration of the crop.