San Jose scale and other scale insects - chemical control

Organophosphates (OPs)
These broad spectrum nerve poisons have been used for control of scale insects in apple orchards for more than 30 years. However, they are toxic to many beneficial species (e.g. natural enemies) in orchards. For these reasons, OPs are less preferred than insect growth regulators for use in IFP. Within the OPs, chlorpyrifos has the advantage of also controlling woolly apple aphid, mealybugs, and caterpillars as well as scale insects; diazinon has the advantage of controlling apple and pear leafcurling midges. Some predatory mites (e.g. Typhlodromus pyri) have developed resistance to OPs since the 1970s and this allowed the development of integrated mite control. These predators assist mite control even where OPs are being applied. The registered chemicals are:

Azinphos-methyl (e.g. Gusathion) - not recommended for scale control in IFP.
Chlorpyrifos (e.g. Lorsban) - not longer recommended for post-bloom scale control in IFP
Diazinon (e.g. Basudin) - only recommended for emergency scale control in IFP

When spraying of an OP for scale control is justified at green tip, it is normally combined with oil to improve coverage and efficacy. However, oil should not be used at green-tip on oil sensitive cultivars such as Cox's Orange. An application of insecticide alone should be applied instead. The post-bloom use of OPs for scale control is no longer recommended in IFP and emergency spraying of diazinon must be specially justified with monitoring data or other extenuating circumstances.