Unexpected crop damage by a pest after a foliar application of an insecticide has been made is often firstly assumed to be because of pest resistance, but commonly there are many other factors why insecticide applications can fail to meet expectations. Before associating insecticide resistance as the reason for crop failure, commonly made mistakes regarding application decisions and practices should be excluded. Many of the reasons for control failures can be avoided by reading product labels carefully and by following label instructions fully. This guideline outlines some of the key factors and considerations for foliar applications of insecticides.