How to Manage Pests
UC Pest Management Guidelines
Scientific Names: Lygus hesperus and Lygus elisus
(Reviewed 8/06, updated 3/09, pesticides updated 10/15)
In this Guideline:
DESCRIPTION OF THE PESTS
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 lygus bug adult is about 0.25 inch long and 0.1 inch wide, flattened on the back. Nymphs resemble adults, but are smaller and do not have wings.
Lygus bug damage may occur in all major apple districts and sometimes is severe. Lygus attack is more frequent in orchards that have a permanent cover crop and in orchards adjacent to crops or vegetation that host lygus.
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. Midseason feeding results in round pits, and late-season feeding causes irregularly-shaped depressions that are similar to stink bug damage.
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 often cause damage and may attack fruit 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. In orchards with a history of lygus damage, monitor fruit at least biweekly between petal fall and harvest to assess need for treatment.
The role of predators and parasites in controlling lygus in orchards has not been investigated, but in cotton and strawberries, beneficials have been shown to be helpful.
Eliminate or suppress weed host plants before fruit forms on trees and thereafter throughout the growing season to minimize lygus populations. Yellow starthistle, Russian thistle, tarweed, sweet clover, wild mustard, lambsquarters, pigweed, shepherd's-purse, wild radish, and vetch are important hosts. Do not mow cover crops or weeds when lygus bugs are present or they will move into the trees.
Organically Acceptable Methods
Cultural and biological control are organically acceptable.
Monitoring and Treatment Decisions
After fruit has formed, sample the cover crop with a sweep net to determine if lygus bugs are present in the orchard. If they are, or if an orchard has had a history of lygus injury, take fruit samples at least every 2 weeks starting soon after petal fall and continue until harvest. Lygus bugs may be present in the orchard but not feeding on the fruit, so you need to check the fruit for damage. Examine a minimum of 100 fruits from trees throughout the block. Because lygus damage is often spotty in distribution, check each 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 apple in 100 is significant for concern and calls for further sampling and evaluation of control needs. 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. Especially be on the lookout for lygus when weeds start to dry up. 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 border trees will hold down numbers and reduce damage.
UC IPM Pest Management Guidelines: Apple
Insects and Mites
L. R. Wunderlich, UC Cooperative Extension, El Dorado County
Acknowledgment for contributions to Insects and Mites:H. L. Andris, UC Cooperative Extension, Fresno County
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
W. W. Coates, UC Cooperative Extension, San Benito County
C. Pickel, UC IPM Program, Sutter/Yuba counties