How to Manage Pests
UC Pest Management Guidelines
DESCRIPTION OF THE PESTS
The grape and obscure mealybugs closely resemble each other. Both mealybugs are most damaging in old trees with rough bark that shelter overwintering egg masses and crawlers. Eggs are yellowish to orange and are laid in a cottony mass. The young crawlers are orange. Mature mealybugs are about 0.2 inch (5mm) long with dark purple-gray, somewhat flattened bodies that are uniformly covered with a white powdery wax. Long caudal filaments along the lateral margin of the body become progressively shorter toward the head.
Mealybugs occasionally feed in the calyx end of maturing fruit, which may become soft as the pear ripens. Because mealybugs cannot be removed with present washing methods, infested lots of fruit are rejected by both cannery and fresh-market handlers. Honeydew is also produced, which may cause russeting on pears and fosters the growth of black sooty fungus on the surface, rendering the fruit unfit for fresh shipment.
Mealybugs are minor pests in pear orchards and only occasionally become pests when their predators and parasites are unable to keep them below economically damaging levels. Mealybugs are most damaging in old trees with rough bark that shelter overwintering nymphs and egg clusters.
At least five species of parasitic wasps attack grape mealybugs in California. Little research on these parasites has been conducted, but it is assumed they play a prominent role in regulating populations. The impact of the different species varies from time to time and place to place. Grape mealybugs that are parasitized by two tiny wasps, Acerophagus notativentris and Pseudophycus angelicus, have multiple emergence holes that are easily seen with a hand lens. Ants must be controlled to keep them from interfering with these natural enemies. Two parasitic wasps, Pseudophycus flavidulus and Leptomastix epona, have been imported and released against obscure mealybugs. To ensure survival of parasites, do not use disruptive insecticides during the growing season.
The most effective mealybug predator is a lady beetle called the mealybug destroyer, Cryptolaemus montrouzieri, which can be found in coastal regions. Cecidomyiid flies prey on mealybug eggs and small larvae. These predators plus green lacewings, minute pirate bugs, and spiders are important in keeping mealybug populations in check.
Organically Acceptable Methods
Biological control and oil sprays are organically acceptable methods.
Monitoring and Treatment Decisions
Mealybugs can be detected during the dormant season by checking under bark and in protected places for overwintering eggs or crawlers. (See DORMANT TO DELAYED-DORMANT SAMPLING for information about monitoring other pests at this time.)
The finger bud to cluster stage is the best time to sample populations to estimate control needs. Collect one fruit spur from the top and one from eye level of 50 trees (100 total) in a block and count the number infested with mealybug nymphs (see SAMPLING AT BLOOM). Continue looking for mealybugs in the fruit calyx through harvest during the weekly fruit sample. (See SAMPLING DURING FRUIT DEVELOPMENT and HARVEST FRUIT SAMPLE for more information.)
Dormant and delayed-dormant oil applications for other pests reduce mealybug populations but are not adequate to control heavy populations. The best time to treat is from cluster bud to bloom when crawlers of the first generation become active. Because of prolonged emergence during June, crawlers of the second generation are more difficult to control. During the cluster bud to bloom period, treat when four or more infested spurs are found.
UC IPM Pest Management Guidelines:
Insects and Mites
L. G. Varela, UC IPM Program, UC Cooperative Extension, Sonoma County