Control of native oyster scale insects.
An outbreak of Quadraspidiotus pyri and Q. ostreaeformis in pome fruit orchards in Switzerland in recent years is reported. Control with mineral oils and the new insect growth regulator diofenolan (formulated as Context) was investigated, with special reference to reducing hazards to predators (especially Coccinellidae) and parasitoids (of which species of Aphytis, Coccophagoides, Encarsia and Pteroptrix were present). Treatments with mineral oil at 3.5% and Context at 0.03% against the crawlers in spring were 94.2-98.7% effective against the diaspidids on apples and pears. Prospects for control of these and other arthropod pests in summer are discussed.