Description of the Pest
Glassy-winged sharpshooter (family Cicadellidae) sucks leaf and stem xylem tissue, and vectors Xylella fastidiosa bacteria lethal to certain crops. While feeding, adults and nymphs excrete large amounts of liquid. When sharpshooters are numerous the excretions accumulate on fruit and foliage giving the appearance of whitewash. Glassy-winged sharpshooter adults feed on over 300 plant species and can reproduce (lay eggs) on about 100 plant hosts.
Sharpshooter nymphs and adults are active insects. When disturbed, they hide by walking rapidly sideways, jumping or flying. The glassy-winged sharpshooter is a larger than most other leafhoppers. Adults are about 0.5 inch (13 mm) long and dark brownish with white and yellowish patches and spots. Pale head spots help to distinguish glassy-winged sharpshooter from the native smoke-tree sharpshooter (Homalodisca lacerta), which has light-colored wavy lines on the head.
Females lay eggs in an egg mass, a cluster of about one dozen eggs, under the epidermis of the lower leaf surface. Eggs initially resemble a greenish blister on the leaf, which females cover with a white chalky secretion to protect them from natural enemies. Eggs turn brown as they mature and leave a permanent brown to gray scar in leaf tissue after nymphs emerge.
Immature glassy-winged sharpshooters develop through five stages (instars) and resemble small adults, except the immatures are wingless, uniformly olive gray, and have prominent bulging red eyes. Smoke-tree sharpshooter nymphs appear very similar but have blue eyes.
The glassy-winged sharpshooter has two generations per year in southern California. However, in recent years the spring generation has become almost undetectable in some areas. Although all life stages can be found year-round, reproduction and immature stages occur mostly from early summer to late fall. Overwintering adults lay eggs from mid-spring through mid-summer. Adults first appear in very low numbers in April and numbers peak in July/August. These late-season adults overwinter until the following season.
Glassy-winged sharpshooter is not considered a damaging pest in avocado. Quarantines may require treatment of nursery stock before young avocado trees can be shipped into uninfested areas of northern California.
Glassy-winged sharpshooter is a serious pest of other crops because it vectors Xylella fastidiosa, a bacterium that causes diseases such as almond leaf scorch, oleander leaf scorch, and Pierce's disease of grapes. No leafhopper-vectored avocado diseases have been observed in the United States. However, strains of Xylella in other parts of the world, such as one reportedly damaging avocado in Costa Rica, could be damaging if introduced into California.
In established avocado groves, glassy-winged sharpshooter generally requires no management because avocados are not a preferred host plant and natural enemies, in particular egg parasites in the family Mymaridae, provide very good levels of control.
However, monitoring may be warranted if avocado are grown near untreated citrus or other favored hosts. Yellow sticky traps are useful for monitoring adults of glassy-winged sharpshooter and their primary parasites (Gonatocerus spp.) Mid-summer through fall are the best times to deploy and inspect traps. Glassy-winged sharpshooters are most common in the second generation (July through Sept, depending on location), when they move into avocado from nearby citrus.
If common in avocado, consider removing or replacing nearby alternate hosts such as favored ornamentals and abandoned citrus. Because glassy-winged sharpshooters reproduce in great numbers on citrus, consult with nearby citrus growers regarding any plans to promote biological control (e.g., conserve egg parasites) or treat sharpshooters in citrus.
Several Gonatocerus spp. wasps parasitize glassy-winged sharpshooter eggs. Parasitized eggs are easily recognized by a tiny, round hole at one end of the glassy-winged sharpshooter egg through which the adult parasite emerged. Gonatocerus ashmeadi is commonly found wherever glassy-winged sharpshooter occurs in California. In southern and coastal areas of California, Gonatocerus walkerionesi, can be very effective in the late summer, when the second generation of eggs are deposited. Gonatocerus novifasciatus, G. morrilli, and G. triguttatus also occur at low levels in California.
Organically Acceptable Methods
Biological control is the only effective, organically acceptable method of contol. Egg parasitoids can provide excellent control of glassy-winged sharpshooters.