Summary An outbreak of the aphid Rhopalosiphum padi (L.) in wheat, oat, and barley crops grown in the Feilding, Halcombe, and Bulls areas attained serious levels during the early summer of 1958. The abnormally dry and warm seasonal conditions are regarded as being primarily responsible. A hurried examination of the problem has provided information which, despite its limitations, is placed on record in view of the desirability of increasing wheat production in New Zealand. Aerial applications of a systemic insecticide (Metasystox) were made in some areas. An endeavour was made to assess the effects of these on aphids and other insects in treated crops. Owing to the fact that the infestations were declining at the time of spraying the results are rather inconclusive.