San Jose scale and other scale pests - chemical control

The same insecticidal chemicals are used to control all the scale pest species on apples. High volume application is very important to ensure good spray coverage. There are three approaches to chemical control. Oils have long been used for the control of scale insects. Since the 1960s, chemical control has been based on the use of broad-spectrum insecticides, such as organophosphates. These highly toxic products have provided effective control of scale insects and other pests but they have had the disadvantage of toxicity to many natural enemies. More recently, effective insect growth regulator compounds combine high toxicity to scale insects with safety to many important beneficial species; and another new compound, a neonicotinoid, has also been registered. Green tip spraying to control scale insects normally involves a combination of oil and insecticide.

IFP aims to eliminate the use of organophosphates in apple orchards and replace these with more selective chemicals, such as insect growth regulators and neonicotinoids. All three groups of chemicals are permitted but the use of organophosphates for the control of scale insects in summer is strongly discouraged; only emergency use is permitted based on monitoring and when no other option is practicable. There are no reports of scale insects in New Zealand developing resistance to insecticides. Sprays for organic growers are limited to oils and lime sulphur.

San Jose scale occurs on a wide range of host plants as well as in the apple orchard itself. A significant part of fruit infestations in summer originate from wind-blown scale crawlers moving from shelter and other host plants. Spraying of shelter in spring and/or summer is a useful part of a shelter management programme and assists scale control. This should be considered if you have spray equipment capable of spraying shelter. Trimming and topping the shelter will help to ensure good spray coverage. If the trunks of the shelter trees are heavily infested with lichen, it may also be necessary to apply a clean up spray of lime sulphur before insecticide.