Pear psylla (a psyllid, family Psyllidae) is an important pest of pear. In addition to damage caused by the psyllid's feeding and honeydew, it vectors a microscopic, pathogenic phytoplasma that causes pear decline disease.

Identification

Adults hold their mostly transparent wings rooflike over their dark brown to reddish brown bodies, resembling tiny cicadas when at rest. A dark spot on the top middle edge of both wings helps to distinguish pear psylla from other psyllid species. The summer adults are about 1/12 inch (2 mm) long. Overwintering adults are somewhat darker and larger, about 1/8 inch (3 mm).

The tiny, elongate, yellowish eggs are barely visible to the naked eye. Nymphs are flattened and up to about 1/10 inch (2.5 mm) long. The first two instars are translucent to yellow with red eyes and black antennae. The third instar is yellowish green and the fourth instar is greenish brown. The fifth instar is black to dark with prominent wing pads. Nymphs' cast skins are commonly brownish or green.

Life Cycle

Pear psylla develops through 3 life stages: egg, nymph, and adult. Adults overwinter in bark crevices, under bark scales of pear trees, or on the ground in organic litter or other places near pear trees. On sunny, winter days when temperatures exceed 45ºF, adults can be observed on tree branches sunning themselves.

Adult females begin laying eggs on or near fruit spurs starting in late January or early February. As buds open, females lay eggs along midribs and petioles of developing leaves or on stems and leaves of blossoms. Each female can lay several hundred eggs during her several week life span.

Pear psylla nymphs develop through five instars. The first four instars can be almost completely covered with the honeydew they excrete. Pear psylla has about five generations per year in California.

Damage

Pear psylla is a greater problem on European varieties than on Asian varieties of pear. It damages pears in several ways. Loss of tree vigor and premature tree death can occur from pear decline, a phytoplasma disease that develops after the psyllid injects its pathogen-contaminated saliva while feeding. Pear decline has varying effects on trees depending on plant care practices, variety, rootstock, quality of the growing site, and pear psylla abundance. Symptoms of pear decline include poor shoot and spur growth, dieback of shoots, reddening and upward rolling of leaves, reduced leaf and fruit size, and premature leaf drop. Sudden tree collapse can result on highly susceptible rootstocks.

Nymphs of the psyllid excrete sticky honeydew that drips onto fruit. This induces the growth of black sooty mold that grows on the honeydew and causes fruit skins to become russeted (darkly discolored). The psyllids also inject a toxic saliva into trees while feeding. This causes portions of the leaf blade to blacken and affected leaves become yellow and sometimes drop prematurely. Overall the psyllid's feeding can slow tree growth and reduce fruit amount and quality.

Solutions

Keep trees growing vigorously with appropriate irrigation and fertilization to reduce the effect of pear psylla and pear decline. Apply horticultural oil at least once during the dormant season and by the beginning of January. If the psyllid and its damage have been abundant, make a second dormant treatment of oil just before bloom. Abamectin plus horticultural applied at petal fall can also give good control.

During the growing season a systemic neonicotinoid such as imidacloprid can be applied. If using systemic insecticide, wait until trees have completed their flowering before making the application because the products can move to nectar and pollen and poison adults of honey bees, parasitoid (parasitic) wasps, and predatory insects that feed on nectar and pollen. To avoid drift from spraying and to avoid trunk injury from injecting insecticide, the preferred application method is to drench imidacloprid onto soil around the base of the trunk as directed on the product label.

References

Adapted from Integrated Pest Management for Apples and Pears, Pest Management Guidelines: Pear, and Pests of the Garden and Small Farm: A Grower's Guide to Using Less Pesticide, University of California Statewide Integrated Pest Management Program (UC IPM).