How to Manage Pests
UC Pest Management Guidelines
DESCRIPTION OF THE PESTS
Lygus bug damage may occur in all major pear districts but is mostly a pest in the Delta region. Lygus damage is more frequent in orchards having permanent cover crops and in orchards adjacent to crops or vegetation hosting lygus. Lygus bugs vary in color from pale green to yellowish brown with reddish brown to black markings, but can be distinguished by a prominent triangle in the center of the back. The adult is about 0.25 inch (6 mm) long and 0.1 inch (2.5 mm) wide, with wing tips that bend down. Nymphs resemble adults, but are smaller and do not have wings. Five black spots are visible on the back on later nymphal instars.
Lygus bugs may feed on developing flower buds early in spring, causing the buds to exude gum and shrivel up. Usually this damage is not serious unless a very heavy infestation is present. Lygus cause their most serious damage by feeding directly on fruit. Mid-season feeding results in round pits, and late-season feeding causes irregularly shaped depressions that are similar to stink bug damage. Peel the fruit and examine the feeding site to distinguish the two types of damage. The area where lygus feeds develops an open pustule. If the flesh of the fruit is examined beneath the pustule, hard cells clustered into a core can be seen. Feeding by stink bugs creates a depression in the fruit with white, pithy areas underneath the skin.
In Delta area pear orchards, the potential for a lygus bug population to cause damage is difficult to assess. Lygus bugs may be present in substantial numbers in the orchard and cause no damage; however, they can feed on fruit, causing damage at any time from petal fall to harvest. Annual preventive treatments are costly and subject to failure because lygus bugs have been quick to develop resistance to chemicals. Use monitoring guidelines to make treatment decisions. In orchards with a history of lygus damage, monitor fruit at least every 2 weeks between petalfall and harvest to assess the need for treatment.
The role of predators and parasites in controlling lygus in orchards has not been investigated.
Reduce or suppress weed host plants before fruit forms and throughout the growing season to minimize lygus populations. Yellow starthistle, sweet clover, wild mustard, and vetch are important hosts. Do not allow cover crops to dry out or to grow excessively between mowings. Orchards located near alfalfa or tomato fields are at a greater risk for damage and lygus infestations may coincide with cuttings or harvest.
Organically Acceptable Methods
Cultural control is an organically acceptable method.
Monitoring and Treatment Decisions
If an orchard has had a history of lygus damage, take fruit samples at least every 2 weeks starting soon after petal fall and continue until harvest. After fruit has formed, sample the cover crop and weeds with a sweep net to determine if lygus bugs are present in the orchard. Lygus bugs may be present in the orchard but not feeding on the fruit, so you need to check the fruit for damage.
Examine the fruit in 40 clusters. (See SAMPLING DURING FRUIT DEVELOPMENT for more information.) Because lygus damage is often spotty in distribution, check each 20-acre block thoroughly. Lygus may migrate into the orchard at any time during the growing season and damage frequently appears first along orchard borders. One damaged pear in 100 is cause for concern and calls for further sampling and evaluation. When sampling fruit for other pests, also look for the presence of lygus bugs on fruit or in the trees to determine if they are still present in the orchard. Because the bugs move quickly and may be difficult to see, the number seen will depend on the skill of the observer. When lygus are migrating into an orchard, periodic spraying of borders will hold down numbers and reduce damage.
Harvest fruit sample
At harvest, assess your IPM program by monitoring fruit in bins for lygus bug damage. Sample 200 fruit from 5 bins per orchard (or 20-acre block in large orchards) for a total of 1,000 fruit. For information on monitoring other pests at this time, see HARVEST FRUIT SAMPLE.
UC IPM Pest Management Guidelines:
Insects and Mites
L. G. Varela, UC IPM Program, UC Cooperative Extension, Sonoma County