San José scale
San José scale (SJS, Diaspidiotus perniciosus) is an extremely important pest of pome and stone fruit. It is a sucking insect that injects a toxin into the plant as it feeds, causing localised discolouration, resulting in fruit being downgraded during processing and packing.
Pest identification
San José scale adult females are yellow with rounded dark grey scales. They are wingless and legless, about 2.5 mm in diameter. Males have a dark band across their back, long antennae, legs and wings. Crawlers are approximately 0.25 mm long and bright yellow.
Damage
San José scale sucks the sap and juice out of the tree and fruit while also injecting a toxin. This causes loss of tree vigour, stunted growth and limb death. On fruit, SJS feeding will cause slight depressions with a red–purple halo. If populations are low, the damage will be concentrated on the bottom of the fruit.
Monitoring
During the growing season, monitor fruit for signs of the red–purple halos caused by the feeding scale insect. Be sure to look closely around the calyx end of the fruit.
Crawlers can be monitored 4–6 weeks after bloom using double-sided tape with a thin layer of petroleum jelly around infested tree limbs. Monitoring during winter should focus on identifying scale colonies on the branches.
Management
San José scale overwinter as immature scale. In spring, the winged males emerge and mate with the wingless females.
Approximately 1 month after the first male flight, the first crawlers can be seen. Understanding this life cycle helps target control and management. Dormant season treatments are the most effective.
Cultural and physical: the most effective cultural control is to prune out infested branches. This will reduce scale insect numbers and open up the tree canopy, improving spray penetration and coverage. Control ant populations as they spread the scale insect crawlers and protect them from natural predators.
Healthy trees supplied with appropriate nutrition and irrigation will be more likely to resist SJS infestation. Good weed management will help ensure minimal competition for resources.
Biological: several natural predators can be used to control SJS. The most common predatory insects and naturally occurring parasitoid wasps include Cryptolaemus (Cryptolaemus montrouzieri), green lacewings (Mallada signata) and Chilocorus beetles (Chilocorus circumdatus). Several fungi and bacteria are available that can infect and kill scale insects; however, these are less likely to reduce populations unless they become abundant. It should be noted that almost all pesticides for SJS control will harm beneficial insect populations.
Chemical: refer to the Orchard plant protection guide for chemical suggestions.
