How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

Sharpshooters are in the same insect family as leafhoppers (Cicadellidae).

Blue-green sharpshooter. The blue-green sharpshooter has green to bright blue wings, head, and thorax, and yellow legs and abdomen, which are visible on the underside. It is about 0.4 inches long. In California they are found in coastal regions near riparian and landscape areas.

The blue-green sharpshooter feeds, reproduces, and is often abundant on cultivated grape. It also feeds and reproduces on many other plants but prefers woody or perennial plants such as wild grape, blackberry, elderberry, and stinging nettle. Mugwort, which is a perennial, is a major breeding host. The blue-green sharpshooter is most common along stream banks or in ravines or canyons that have dense growth of trees, vines, and shrubs. It can also be abundant in ornamental landscaping. Because it feeds on succulent new growth in areas of abundant soil moisture and shade, it is seldom found in unshaded, dry locations but also finds plants in constant deep shade unattractive.

The blue-green sharpshooter has one generation a year in most of California and a second generation in some parts of the state. They overwinter in riparian vegetation. In late winter and early spring, adults become active, and a small percentage begin moving into nearby vineyards for feeding and egg laying starting just after budbreak. Their movement into vineyards increases as natural vegetation dries up. Eggs hatch from May through July. Some of the nymphs become adults by mid-June, and the number of young adults continues to increase through July and August. In August when grape foliage is less succulent, blue-green sharpshooters begin to move back to nearby natural habitats. Populations of blue-green sharpshooter are always larger in natural vegetation than in vineyards.

Glassy-winged sharpshooter. The glassy-winged sharpshooter, is a large insect compared to the 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 help distinguish glassy-winged sharpshooter from a close relative, smoke-tree sharpshooter (H. lacerata), which is native to the desert region of southern California and slightly smaller in size. The head of the smoke-tree sharpshooter is covered with wavy, light-colored lines, rather than spots. Immature stages (nymphs) of the glassy-winged sharpshooter are smaller than the adult, wingless, uniform olive-gray in color, and have prominent bulging eyes.

Females lay their eggs in masses of up to 28 in the lower leaf surface of young leaves that have recently expanded. 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, making them easy to see. Shortly after egg hatch, the leaf tissue that contained the egg mass begins to turn brown. The dead leaf tissue remains as a permanent brown scar.

Nymphs emerge in 10 to 14 days and proceed to feed on leaf petioles, small stems, and leaves while they progress through five molts before becoming winged adults. There are two generations a year.

Glassy-winged sharpshooter has become established in most of southern California. It remains localized in central and northern California where eradication programs are being conducted to confine its spread. It occurs in unusually high numbers in citrus and avocado groves and on numerous kinds of plants in irrigated ornamental landscapes, riparian areas, and native woodlands.

Green sharpshooter and red-headed sharpshooter. The green sharpshooter prefers lush dairy pastures, permanent grasses, and areas that are continually irrigated. They favor watergrass, bermudagrass, Italian rye, perennial rye, and fescue for food. Red-headed sharpshooters feed and breed only in areas where bermudagrass grows. Grapes are accidental hosts of these grass-feeding sharpshooters. In central California, insect movement is usually to the east (downwind at dusk) of pastures, weedy hay fields, or other grassy areas. The presence of neighboring hay fields or permanent pastures should be considered when planting a vineyard.

The green and red-headed sharpshooters have three generations per year. They overwinter as adults and lay eggs from late February to early March. The overwintering adults do not live long, thus it is probably the second generation that moves into the vineyard.

DAMAGE

Sharpshooter feeding does not cause damage in grape; however, these insects vector the bacterium Xylella fastidiosa, which causes Pierce's disease in grapes. (This bacterium also causes alfalfa dwarf disease and almond leaf scorch in California.) The blue-green sharpshooter is the most important vector of Xylella fastidiosa in coastal grape-growing areas. The glassy-winged sharpshooter is the primary vector in the Coachella Valley, Temecula, and Kern County. The green sharpshooter and the red-headed sharpshooter are present in coastal areas, but they serve as the primary vectors in most areas of the Central Valley.

When sharpshooters feed on vines, they inject the bacterium, which multiplies in the water-conducting system and causes water stress of the plant. Symptoms from early spring infections may become visible by fall of the year infected, but that is variety dependent. In vines infected the previous year, budbreak will be delayed or absent in spring, and leaf scorch appears by early summer and increases through fall, causing clusters to dry. Early-season infections (March-May) are more likely to survive the next winter than late summer infections and become chronic. Xylella fastidiosa can kill vines 1 to 3 years after infection.

The glassy-winged sharpshooter feeds much lower on the shoot in summer than do the other sharpshooter vectors in California. It also feeds at the base of second-year canes, which may increase the number of late-season infections that survive the winter and become chronic infections. Feeding by this sharpshooter also occurs during winter on one- to two-year old vines and can transmit the bacterium even during dormancy. If the inoculum enters the wood below where winter pruning cuts are made, the feeding can lead to chronic infections. Rather than the generally linear increase in Pierce's disease incidence over several years that has been experienced where other sharpshooters are the vectors, glassy-winged sharpshooter may increase the rate of vine-to-vine spread of Pierce's disease during a single season. Growers should try to reduce numbers of glassy-winged sharpshooter whenever they are present in vineyards.

MANAGEMENT

Pierce's disease control is based entirely on preventing infection. Do not allow vectors to enter vineyards from areas adjacent to vineyards, especially during spring months. Immediately remove vines with Pierce's disease symptoms as soon as they are seen in all vineyards subject to influxes of glassy-winged sharpshooter. Vineyards within 0.5 to 1 mile of citrus or avocado groves are at greatest risk.

Insecticide treatments aimed at controlling the vector in areas adjacent to the vineyard have reduced the incidence of Pierce's disease by reducing the numbers of sharpshooters immigrating into the vineyards in early spring. The degree of control, however, is not effective for very susceptible varieties such as Chardonnay and Pinot Noir or for vines less than 3 years old. If a vineyard is near an area with a history of Pierce's disease, use varieties that are less susceptible to this disease.

Monitoring and Treatment Decisions for Blue-green and Glassy-winged Sharpshooters
The best time to start assessing the need for managing the blue-green or glassy-winged sharpshooters is at budbreak. Monitoring at this time will enable you to observe movement of sharpshooters into your vineyard from surrounding vegetation.

• Monitor for glassy-winged sharpshooter in all vineyards through late summer.
• Monitor blue-green sharpshooter in coastal vineyards and in vineyards with a history of problems until late May or 1 month after treatment.
• From May to July, make visual searches and sample with a sweep net riparian areas or ornamental landscapes adjacent to the vineyard.

To monitor for sharpshooters:

• In late February just before budbreak, place several double-sided yellow sticky traps (at least 4x7 inches for bluegreen sharpshooters and 9x11 for glassy-winged sharpshooter) in areas adjacent to vineyards that serve as habitat for sharpshooters, such as riparian areas and ornamental landscapes.
• In the vineyard place a minimum of 6 traps per block, 100-200 feet apart for blue-green sharpshooters. Be sure that some of the traps are placed 50 feet within the vineyard perimeter. For glassy-winged sharpshooter, place one trap per 10 acres within 30 feet of the vineyard perimeter, especially on edges adjacent to alternate hosts such as citrus.
• Check traps once per week beginning at budbreak and more frequently after 2-3 days of warm weather. Continue to monitor traps for blue-green sharpshooters until late May or for a month after treatment. Monitor traps for glassy-winged sharpshooters throughout the season until daytime temperature remains below 65°F.
• Remove insects from the trap after counting and recording on a monitoring form (example form—162 KB, PDF).
• Replace traps every 2 weeks or when they become excessively dirty or discolored and especially on edges adjoining other alternate glassy-winged sharpshooter hosts such as citrus.

Treatment is warranted for blue-green sharpshooters if:

• After successive warm days above 70°F, there is a sharp increase in the number of sharpshooters trapped.
• More than an average of 7 are caught per trap/week in riparian or ornamental habitats.
• Visual inspections reveal more than 1 sharpshooter/vine.

Treatment is warranted for glassy-winged sharpshooters if:

• They are present in the vineyard.

Blue-green sharpshooters. Treat vegetation along the edges of the vineyard where sharpshooters are observed. If sharpshooters have migrated into the vineyard and new shoot growth on grapevines is longer than a few inches, also treat the first 200 to 300 feet in from the edge of the vineyard. Replace traps after spraying and continue monitoring traps and vegetation. Respray if trap catches indicate another population increase. The goal is to eliminate more than 95% of the vector population.

Riparian vegetation management has proven to be effective in reducing the damaging spring populations of blue-green sharpshooters. Because these areas are ecologically sensitive and regulated by federal, state, and local legislation, the unauthorized removal of vegetation is prohibited or restricted. Vegetation management of these areas must be acceptable or beneficial for wildlife and water quality and maintain the integrity of the riparian habitat. For additional information, contact the California Department of Fish and Game for current regulations and guidelines. For more information, see the complete Riparian Vegetation Management for Pierce's Disease in North Coast California Vineyards.

Glassy-winged sharpshooter. In addition to trap monitoring, do visual searching to monitor for eggs, nymphs, and adults. Combine the visual search with the leafhopper and mite sampling. Management of glassy-winged sharpshooter in vineyards adjacent to other host crops is best if done on an areawide basis. This approach relies on monitoring agricultural crops, vineyards, and other plant species, and treatment of overwintering hosts. Apply insecticide treatment to vineyards if any glassy-winged sharpshooter life stage is discovered in a vineyard or if there is a potential for movement of this pest into the vineyard. Systemic insecticides (imidacloprid) are currently the most effective materials for control of glassy-winged sharpshooter in vineyards.

Monitoring and Treatment Decisions for Green and Red-headed Sharpshooters
In the Central Valley, insecticide treatments for these sharpshooters are of little value overall because overlapping generations result in the continuous presence of eggs inside protective leaf tissues of host plants from February through fall. Sprays are not effective against eggs. In alfalfa fields, orchards, or field-crop areas, the grass weeds growing in or at the margins of the crop support green sharpshooter populations, and red-headed sharpshooter populations are supported in areas with bermudagrass. Eliminate weedy grasses whenever possible. Monitor with a sweep net areas of grass weeds that are adjacent to the vineyard and cannot be eliminated. (Green and red-headed sharpshooters are not attracted to yellow sticky traps and must therefore be monitored with a sweep net.) An average catch of two or more sharpshooters per 50 sweeps in a total of 400 sweeps is cause for concern. About all that can be done is to try to purchase or lease adjacent properties and manage them so that sharpshooter populations do not build up.

IMPORTANT LINKS

• Photos of sharpshooters
• Sampling for sharpshooters using sticky traps (162 KB, PDF)

PUBLICATION

UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Research Center, Parlier
L. G. Varela, UC IPM Program, Sonoma County
F. G. Zalom, Entomology, UC Davis
R. J. Smith, UC Cooperative Extension, Sonoma County
A. H. Purcell, Environmental Science, Policy and Management, UC Berkeley
P. A. Phillips, UC IPM Program, Ventura County
D. R. Haviland, UC IPM Program, Kern County
K. M. Daane, Kearney Agricultural Research Center, Parlier
M. C. Battany, UC Cooperative Extension, San Luis Obispo County
Acknowledgment for contributions to Insects and Mites:
J. Granett, Entomology, UC Davis

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