How to Manage Pests

UC Pest Management Guidelines

The glassy-winged sharpshooter is a large insect compared to other leafhoppers. Adults are about 0.5 inch long and are generally dark brown to black when viewed from the top or side. The abdomen is whitish or yellow. The head is brown to black and covered with numerous ivory to yellowish spots. These spots are helpful in distinguishing glassy-winged sharpshooters from smoke-tree sharpshooters, which have light-colored wavy lines on the head.

Females lay their eggs in masses of about 10 to 12 in the lower leaf surface of young, fully developed leaves. When it is first laid, the egg mass appears as a greenish blister on the leaf. The female covers the leaf blister with a secretion that resembles white chalk and is more visible than the leaf blister. Nymphs hatch in 10 to 14 days and proceed to feed on the leaf petioles or small stems.

The glassy-winged sharpshooter has two generations per year in California. In late winter and early spring, adults become active. Citrus is an especially attractive egg-laying host during late March through April and again in late June through August. The first generation of glassy-winged sharpshooter become adults by mid-June, and the number of young adults continues to increase through July and August. Glassy-winged sharpshooter will overwinter in citrus as well as weeds, ornamentals, and various trees.

DAMAGE
Glassy-winged sharpshooter feeds on the nutrient-poor xylem of the plant and must consume copious amounts of fluid in order to gain enough nutrition to grow and reproduce. Consequently, the adults and nymphs excrete large amounts of liquid while feeding, which gives the fruit and foliage a whitewashed appearance.

Preliminary data suggest that high populations of glassy-winged sharpshooter may have an impact on growth and vigor of coastal lemons. However, as yet there is not sufficient data to suggest that treatments should be applied to glassy-winged sharpshooter populations on citrus other than for the purpose of reducing populations that might move to grapes or to disinfest citrus trees before harvest. Glassy-winged sharpshooter has been reported as a vector of the Xylella fastidiosa strain of bacteria that causes citrus variegated chlorosis; however, this disease has not yet been found in the U.S.

The glassy-winged sharpshooter is a serious pest of grapes because it acts as a vector of the strain of Xylella fastidiosa that causes Pierce's disease in vineyards. It also vectors the strain that causes oleander leaf scorch in oleander. The bacteria multiply and block the water-conducting system of the plant causing water stress and eventual plant death. There is no known cure for the disease. Because many glassy-winged sharpshooters overwinter in citrus, citrus acts as a source of sharpshooters for neighboring vineyards.

MANAGEMENT
To protect vineyards in uninfested areas of the state, quarantine regulations are in effect to slow the spread of glassy-winged sharpshooter from southern California and parts of Tulare and Kern counties northward. Kern County and Tulare citrus orchards in the glassy-winged sharpshooter-infested areas must be disinfested of glassy-winged sharpshooter before citrus fruit can be harvested and shipped to uninfested regions such as northern Tulare County packinghouses. Nursery citrus trees must be disinfested before they can be shipped to uninfested areas. In infested areas of the state, citrus orchards with high densities of glassy-winged sharpshooters are treated to bring the overall population levels down and reduce the threat of sharpshooters in nearby vineyards. Although biological control agents are being sought, management primarily involves treatment with insecticides.

Biological Control
The egg parasitic wasp, Gonatocerus ashmeadi, is commonly found wherever glassy-winged sharpshooter occurs in California. In the southern and coastal areas of California a closely related species, Gonatocerus morrilli, can be a very effective parasite in the late summer, when the second generation of eggs are deposited. Parasitized glassy-winged sharpshooter eggs are easily recognized by a tiny, round hole at one end of the egg through which the adult parasite emerged. Neither G. ashmeadi nor G. morrilli, however, is effective during the first generation of glassy-winged sharpshooter egg laying. Surveys of other regions of the United States and Mexico are under way to obtain additional species of wasps that may complement and improve biological control of this pest.

Organically Acceptable Methods
There are no organically acceptable methods.

Selectivity
Most selective insecticides are not quick enough or effective enough to reduce glassy-winged sharp-shooter to acceptable levels. Pyrethrins are selective because they are extremely short-lived but they are variable in their efficacy. Systemic imidacloprid (Admire) is the next most selective insecticide because it only affects vedalia beetles. The foliar neonicotinoids, pyrethroids, and methomyl are highly toxic to most natural enemies.

Monitoring and Treatment Decisions
Glassy-winged sharpshooter insecticide treatments are only recommended in citrus for one of two reasons: to suppress glassy-winged sharpshooters in the orchard in order to reduce the risk to neighboring grape vineyards or to disinfest fruit just before harvest. Different insecticides are recommended for each purpose. Insecticide treatments should be avoided where possible because of their potential for disrupting biological control of citrus pests.

Glassy-winged sharpshooter suppression: An insecticide treatment in citrus may be needed to reduce overall numbers so that there are fewer glassy-winged sharpshooters to vector Xylella in neighboring grapes. When the weather is cool (winter, early spring), glassy-winged sharpshooter is best monitored in citrus by beating branches of 20 citrus trees per 10-acre block and counting the number of glassy-winged sharpshooter adults and nymphs that fall onto the sheet. An average of more than one per tree is considered a potential threat to neighboring vineyards. During the warmer weather, especially when egg masses are present during April and June–August, it is easier to conduct a timed search. During a 3 to 5 minute examination of each of 20 trees per 10-acre block, count the number of nymphs, adults, and live egg masses observed. Infestations of more than one mobile stage (nymph or adult) and more than one egg mass per tree are considered significant.

Disinfestation of trees just before harvest: The other reason for insecticide control of glassy-winged sharpshooters in citrus is to disinfest trees immediately before harvest so that fruit can be shipped from a generally infested region (such as southern California or Kern County) to an uninfested area (such as northern Tulare County) for packing. To detect mobile stages of glassy-winged sharpshooter, stuff citrus foliage into a sweep net, shake vigorously, and inspect the contents of the net. If any live, mobile glassy-winged sharpshooter stages are found, a treatment is needed. Treatment should be as close to harvest as the preharvest interval and restricted entry interval allow (this interval is noted in the treatment table as the minimum days before harvest). Glassy-winged sharpshooter is a very mobile pest and can rapidly move into the treated orchard from untreated areas as soon as insecticide residues begin to break down.

PUBLICATION

UC IPM Pest Management Guidelines: Citrus
UC ANR Publication 3441
Insects, Mites, and Snails
E. E. Grafton-Cardwell, Kearney Agricultural Center, Parlier
J. G. Morse, Entomology, UC Riverside
N. V. O’Connell, UC Cooperative Extension, Tulare Co.
P. A. Phillips, UC IPM Program, UC Cooperative Extension, Ventura Co.
C. E. Kallsen, UC Cooperative Extension, Kern Co.
D. R. Haviland, UC Cooperative Extension, Kern Co.
Acknowledgments for contributions to the insect, mite, and snail section:
J. Barcinas, E. S. I., Corona, CA
R. Dunn, Badger Farming Co., Exeter, CA
J. Gorden, Pest Management Associates, Exeter, CA
H. Griffiths, E. S. I., Corona, CA
D. Machlitt, Consulting Entomology Services, Moorpark, CA
C. Musgrove, retired entomologist, Riverside, CA
K. Olsen, S & J Ranch, Pinedale, CA
T. Roberts, E. S. I., Corona, CA
J. Stewart, Pest Management Associates, Exeter, CA
P. Washburn, Washburn & Sons Citrus Pest Control, Riverside, CA

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