According to the University of Rhode Island Horticulture Program, pear trees are fairly resistant to insects. It is more likely that your pear tree will have a disease problem rather than an insect problem. However, some pests can affect pear trees, and sprays can be applied to treat the problem.
Pear psylla has been present in the United States since 1882, predominantly in the eastern part of the country. It was discovered in Washington State in 1937 and now exists all over the U.S. and Canada. It creates four generations per year and has four stages of development: adult, egg, small nymphs and large nymphs. Adults look something like a cicada and are either reddish brown (overwintering type) or tan to brown (summer variety). The winter type becomes active when temperatures reach 50 degrees. They mate and lay eggs along the bark in cracks and scars before the buds emerge in spring. Later generations are laid on the emerging leaves usually near the midrib. The nymphs hatch and seek the tender new leaf growth to feed on, forming a honeydew drop over themselves as they feed. The honeydew drips onto leaves and fruit and when exposed to bright light, can scorch the leaf tissue. The honeydew provides an excellent place for sooty mold to take hold. It can ruin the pear fruit. Severe infestations can cause "psylla shock"--too much toxin absorbed from the honeydew by the tree, causing the tree to shed its leaves.
Treating Pear Psylla
Dormant oil should be applied in April before buds begin to swell. This will help prevent the adults and their newly hatched nymphs from having anything to feed on. A second application of dormant oil can be applied seven to 10 days later, still before buds have bloomed. The dormant oil should have a 2 percent solution. Through the summer, insecticidal soap is effective against nymphs. It should be applied every 10 to 14 days as long as nymphs are present.
Plum curculio attacks more than just plum trees. The destructive beetle is drawn to stone fruit and apple trees. It bores into the fruit and feeds on the pulp. The females leave a crescent-shaped scar where they have laid eggs. Curculio passes through four stages: egg, larva, pupa and adult. Their activity is stimulated by moisture and warmth, both ample in the spring.
Treating Plum Curculio
Imidan, which goes by the trade name Phosmet, is effective in treating curculio. It should be sprayed after petal-fall but before fruit begins to develop. This tends to occur in May to June, depending on your planting zone. Wait until 75 to 90 percent of the petals have fallen before applying. If you spray too early, the insecticide could affect pollinating insects and reduce your pear harvest. Once fruit develops, the insecticide should not be applied, because it renders the fruit inedible.
Codling moths attack walnut, pear and apple trees, boring into the fruit and leaving 20 to 90 percent of it damaged or inedible. The larvae overwinter in debris at the base of the tree and emerge from their cocoons in the spring. If not treated, the moth population can get out of control in as little as one or two seasons. It may take several seasons of treatment with insecticide to bring it back under control. Insecticide must be applied as eggs are hatching. If the worms get inside the fruit, they are not affected by the spray. Start checking the tree about three weeks after bloom and watch for tiny marks, called stings, on the fruit. Remove any fruit with stings to reduce the risk of the larvae inside emerging. Spray the tree with an insecticide containing spinosad, a product safe for people, pets and beneficial insects. It lasts for only 10 days and must be reapplied every 10 to 14 days to control the moth population. A maximum of six applications per summer is recommended, and applications should cease seven to 10 days prior to harvest.