How to Manage Pests
UC Pest Management Guidelines
DESCRIPTION OF THE PESTS
Several aphid species occasionally attack pears; the most common are green peach aphid, cotton aphid (also known as melon aphid), and bean aphid (also known as dock aphid). These aphids overwinter as adults on various weeds and field crops in or outside the orchards. Usually after pear bloom, when trees are growing rapidly, these aphids appear on foliage and shoots, establishing colonies, and several generations may occur in cool spring weather.
Green peach aphid is light green in color. On adults a dark blotch in the middle of the abdomen serves to distinguish this species from others. Cotton aphid is generally dark green, but immature forms may be yellowish. Bean aphid is dark-colored and seems to prefer sucker shoots in the center of the tree. Both green peach aphid and cotton aphid attack shoots all over the tree.
Aphid feeding causes pear foliage to curl and the growth of shoots to be stunted. This type of injury is of minor importance. Most of the damage is caused from aphids feeding directly on fruit and producing honeydew, which falls on the fruit. Honeydew causes fruit lenticels to darken, giving the pear a russeted appearance. The presence of honeydew also makes the fruit sticky, and a black fungus grows in this honeydew, giving the fruit a sooty appearance. This contamination and russetting will cause fruit to be culled from fresh shipping.
Aphids are infrequently encountered in pear orchards and seldom require special treatment unless the weather remains cool throughout spring and early summer. Aphids generally serve as a valuable early-season food source for insect predators. With the onset of warm weather, aphids leave pear trees for other hosts and do not reappear until the following spring.
Predators and parasites often reduce aphid populations, making chemical treatment unnecessary. Predators of aphids include lady beetles (Hippodamia convergens, Coccinella spp.), green lacewing larvae (Chrysoperla carnea), and brown lacewing larvae (Hemerobius spp.). Parasites of green peach aphid include Aphelinus semiflavus, Aphidius matricariae, Diaeretiella rapae, and Lysiphlebus testaceipes. A common cotton aphid parasite is Lysiphlebus testaceipes; parasites in the Lysiphlebus and Diaeretiella genera attack bean aphid. Delay chemical control as long as possible to allow biological control and hot weather to reduce aphid populations.
Organically Acceptable Methods
Use biological control and sprays of approved narrow range oils or neem oil to control aphids.
Monitoring and Treatment Decisions
When aphids are present in the spring and early summer, inspect fruit and foliage for fine droplets of honeydew to assess potential from honeydew damage. This can be done when sampling for other pests (see SAMPLING DURING FRUIT DEVELOPMENT). No specific criteria have been developed to project the severity of injury according to the honeydew found, so use your best judgment. Damaged fruit is not culled from No. 1 cannery shipment, so the decision for determining if a population requires treatment is not as critical as it is with pests that can cause the need for culling from both fresh and cannery markets. A spray is economically justified for fresh-market pears if a difficult and costly sorting will be required.
UC IPM Pest Management Guidelines:
Insects and Mites
L. G. Varela, UC IPM Program, UC Cooperative Extension, Sonoma County