Pear Psylla (Cacopsylla pyricola)
Pear psylla is a very small sap-feeding insect and is considered the most serious insect pest of pear in the United States. Serious infestations can stunt, defoliate, and even kill trees. Psylla feeding produces copious amounts of sticky honeydew that can cause fruit russeting. All commercial pear varieties are attacked, although smooth skinned pears are more injured than russeted varieties, and Asian and red pears are less prone to injury than European and green pears.
Nymphs are about 1.6 mm long and light yellow, they're cylindrical, but appear flattened.
Adults are 2.5 mm long, and tan to light brown with clear wings.
Eggs are minute, oval, and creamy white to yellow.
- Large amounts of honeydew, making the tree sticky and promoting the growth of sooty mold.
- Dark russet blotches or streaks on fruit.
- Stunted shoots.
- Small or curled leaves.
- Reduced fruit size.
- Twig dieback.
- Premature leaf drop.
- Stunted growth, wilting, defoliation, and fruit drop.
Chemical control is difficult because the pear psylla rapidly develops resistance to insecticides. It has already developed localized resistance to pyrethroids all across its range. As such, it is very important to alternate between pesticide classes to prevent or slow resistance.
Cultural and Mechanical Controls:
As populations of psylla increase rapidly on highly vigorous trees, avoid practices that overstimulate tree growth.
- Apply the minimum amount of nitrogen fertilizer necessary to achieve adequate fruit set and good fruit size.
- Avoid summer pruning which encourages shoot growth.
- Pull off water sprouts or suckers growing from scaffold limbs through the center of the trees in order to remove tender foliage that psylla feed on and also to allow sprays to penetrate better. Pull water sprouts by hand rather than cutting them with loppers to minimize regrowth.
A number of predators and at least two parasitoid species attack pear psylla in Washington. The common predators include:
- anthocorid bugs
- predaceous plant bugs
- lacewing adults and larvae
- ladybird beetle adults and larvae
Two parasitoid wasps—Trechnites psyllae and Prionomitus mitratus—lay eggs inside the bodies of psylla nymphs where the wasp larvae consume the psylla host as they develop.
Effectiveness of biological control increases in orchards where fewer codling moth treatments are applied such as in mating disruption blocks.