Pear Psylla

Pear psylla is one of the most serious insect pest of pears because of its ability to develop resistance to insecticides and to vector the pathogen that causes pear decline.

Overwintering pear psylla adults are somewhat darker and larger (0.125 inch or 3 mm) than summer adults (0.08 inch or 2 mm). Adults hold their transparent wings rooflike over their dark to reddish brown bodies when at rest; they resemble tiny cicadas. A dark spot on the top middle edge of both wings helps to distinguish pear psylla from other psylla. Tiny, elongated yellowish eggs, which are barely visible without a hand lens, are laid 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. Pear psylla nymphs pass through five instars, four of which are almost completely encased in honeydew. When first hatched, the tiny nymphs are yellow with red eyes and black antennae. The third stage is yellowish green and the fourth greenish brown. The fifth instar is called the hardshell stage and it is dark with prominent wing pads.

Pear psylla is a greater problem on European varieties than on Asian varieties. Pear psylla damages pears in several ways. Loss of crop and tree vigor, and sometimes loss of trees, can occur from pear decline disease, caused by a phytoplasma organism that psylla injects into pear trees. Pear decline has varying effects on the trees depending on variety, rootstock, quality of the growing site, and pear psylla numbers.

Honeydew, produced by psylla nymphs as they feed, drops onto fruit. A black sooty mold grows on the honeydew and the fruit skin russets, which downgrades fruit for fresh-market use. Psylla feeding and injection of a toxin into the tree causes portions of the leaf blade to blacken, and leaves to yellow and sometimes fall. Growth and productivity of the tree can be severely reduced for one or more seasons.

Pear psylla management in California is aimed at holding psylla populations at low levels throughout the year. Populations that are allowed to reach high levels become difficult to control, especially if they migrate in fall. Use one or two dormant sprays to reduce populations to no more than 1 psylla per 100 beat-tray samples by the time trees break dormancy.

If the overwintering adult population is adequately reduced before egg laying starts in late January or early February, the population can usually be kept low throughout the foliage season by petroleum oil, applied alone or added to sprays for other pests, and by natural enemies.

If overwintering psylla adults lay eggs before the dormant spray is applied, however, a higher base population is present all season. This makes control difficult because when generations overlap, all life stages are present, and not all stages are susceptible to chemical treatments. It is essential to keep populations low through summer and after harvest to prevent migration of adults in fall. If substantial numbers of adults overwinter outside the orchard and migrate in after application of dormant sprays, success of the management program will be limited.

There are many naturally occurring predators and parasites of pear psylla including green lacewings, brown lacewings, and minute pirate bugs. Nonselective codling moth insecticides destroy many of these beneficials, resulting in outbreaks of this pest. Orchards in a codling moth mating-disruption program generally have greatly reduced levels of pear psylla. In addition, some codling moth and psylla insecticides destroy mite predators and chronic mite problems will develop.

Although predators and parasites may not provide complete control in commercial orchards, they may maintain psylla populations below economically damaging levels when supplemented with a year-round program of oil treatments. Predation is probably occurring when top shoot samples show only one to several psylla nymphs per infested shoot; in the absence of effective predation, there are apt to be 10 or more psylla nymphs on a shoot because each female psylla lays 10 to 20 eggs at a time.

To reduce the effects of pear decline, use Winter Nelis, Old Home x Farmingdale, or Pyrus betulaefolia seedlings for rootstock and maintain pear psylla populations at low levels.

Organically acceptable methods include biological and cultural control and sprays of approved oil, insecticidal soaps, azadirachtin, and kaolin clay.

Psylla control is best accomplished in the dormant season, but if psylla have dispersed out of the orchard and into areas where they won't be treated, dormant control becomes more difficult. Monitor psylla populations year round to predict and prevent outbreaks and movement of adults from the orchard.

• In December, monitor overwintering adults with 100 beating tray samples (each beat sample consists of three taps).
• Beginning in February, monitor eggs by sampling 100 fruit spurs. For additional information, see DORMANT TO DELAYED-DORMANT SAMPLING.
• At bloom, monitor nymphs and eggs by clipping one flower cluster from the top and one from eye level of 50 trees (100 total) and counting nymphs and eggs on the cluster. For additional information, see SAMPLING AT BLOOM.
• During fruit development, take weekly shoot samples: one from the top and one from eye level of 20 trees per block. Examine 5 leaves per shoot for pear psylla nymphs, eggs, and honeydew. As the season progresses, sample the top shoots because psylla will become concentrated on the new growth at the tops of trees where good spray coverage is hardest to achieve. For more information regarding sampling for other pests at this time, see SAMPLING DURING FRUIT DEVELOPMENT.
• At harvest, examine 200 fruit per bin from 5 bins per orchard (or 20-acre block in large orchards) for a total of 1,000 fruit for honeydew and sooty mold. For additional information on this sample, see HARVEST FRUIT SAMPLE.
• After harvest, collect one top shoot and one eye-level shoot from 20 trees and examine 5 leaves on each shoot for psylla eggs and nymphs. Count the number of shoots infested. For additional information, see SAMPLING AT BLOOM.

Dormant season

Each winter make one or two dormant oil sprays to reduce overwintering populations to no more than one adult psylla per 100 beating tray samples. If there are an average of two or more adults per 20 beat samples, apply at least one dormant treatment. If there are more than 50 adults per 50 beat samples, two treatments will be needed.

Growing season

Use the following control action thresholds to determine if treatments are necessary during the growing season.