San José scale: how to recognise and treat it

Pest

San José scale — Photo: Zihao Wang, CC BY 4.0, Wikimedia Commons

Symptoms

Grey, crusty coverings of tiny round scales, about 2 mm across, on bark, twigs and fruit.
A red or reddish-purple ring around each scale on young twigs and fruit.
Gumming on the bark and dying twigs and branches.
Heavily infested trees lose vigour and crop, and limbs or whole trees can die.

Organic treatment

Spray horticultural oil in the dormant season to kill the overwintering young scales, but not on plum and walnut, which dormant oil can damage.
In the growing season, spray oil 2–3 weeks after the first tiny yellow crawlers appear on double-sided sticky tape.
Protect the lady beetles and parasitic wasps that keep the scale down; control ants.

Chemical treatment

For heavy infestations, oil combined with pyriproxyfen or buprofezin; follow the label dose and pre-harvest interval.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Prevention

From spring, wrap double-sided sticky tape round infested twigs to see when the crawlers hatch.
Avoid broad-spectrum insecticides, which kill the scale's natural enemies.
Where the scale is common, spray dormant oil every winter.

Plants it affects

Sources

Figures checked against these sources.