The recent discovery of an invasive insect in California Costco stores has gardeners on the lookout across the West.

In April and May California Department of Agriculture inspectors from multiple counties in California found glassy-winged sharpshooters on grape plants shipped from a nursery in Fresno to Costco stores in northern counties.

To reduce new introductions and spread of the glassy-winged sharpshooter in Arizona, the Arizona Department of Agriculture has established quarantine regulations on grapevines from California. Vines must be grown in nurseries compliant with a glassy-winged sharpshooter management plan which includes pest exclusion, insecticidal treatments and inspections. Plants that are not compliant cannot be sold in Arizona.

Considering the potential for the spread of Pierce’s disease, caused by the bacterium Xylella fastidiosa which the insects can transmit, it is important that Arizona homeowners purchase grapevines only from Arizona retail outlets and not bring them in from out of state, as it is possible that these grapevines will not be treated or inspected properly. Homeowners should also watch for sharpshooters on their plants and remove any plants that appear to be diseased.

Early detection is still one of the most important tools for limiting spread and potential crop impacts.  Use of insecticides for glassy-winged sharpshooters, removal of adjacent weeds and maintaining plant health through good irrigation and fertilization practices will also limit the impact of the disease.

The glassy-winged sharpshooter is invasive in the West.

Native to the southeastern U.S. and Mexico, the species Homalodisca vitripennis can draw more than 300 times its own body weight in plant xylem fluid from the plants they feed on. Infested plants then require increased irrigation to survive. The insects feed on over 600 different plants worldwide, including landscape plants, vegetables, and fruits, including grape vines. 

The sharpshooter species has periodically been detected in Arizona monitoring traps, and there are native blue-green sharpshooters here. Both glassy-winged and native sharpshooter adults are large, measuring up to half an inch long. They have a distinctive bullet-shaped body, large prominent eyes and distinct color spots.

These sharpshooters both vector a strain of the bacterium Xylella fastidiosa which causes fatal wilting, scorch, and dieback diseases on grapes, almond, alfalfa and weeds. In grapes, this disease is known as Pierce’s disease.

Pierce’s disease is endemic in southern Arizona grape-growing regions and is spread by native sharpshooters. Other strains of Xylella fastidiosa infect oleander, olive, citrus, peach, pecan or oak. However, not all strains of Xylella fastidiosa are found in the United States, and the severity of the disease on these crops varies.

For more information about Pierce's disease in grapes, see this Extension publication. For general information about grape growing challenges, see this publication.