In the late 1990s, California table grape growers feared that a newly invasive pest, the glassy-winged sharpshooter (Homalodisca vitripennis) would fly into vineyards and spread Xylella fastidiosa, an endemic species of bacteria known as the cause of Pierce’s Disease. In response, local public and private organizations snapped into action and developed the General Beale Pilot Project, a coordinated effort at integrated pest management, over an area of 50 square miles, involving local growers, pest control advisors, commodity organizations, universities, and government agencies. (Image originally published in Haviland et al 2021, Journal of Integrated Pest Management)

By David Haviland

David Haviland

Insect-vectored diseases present some of the most difficult challenges to modern-day pest managers. This is especially true when the vector is highly polyphagous and mobile and there is no cure for the disease.

In the late 1990s, California table grape growers found themselves in a very difficult predicament. A newly invasive pest, the glassy-winged sharpshooter (Homalodisca vitripennis), had become established and high populations of overwintering adults were being found in neighboring citrus orchards in the lower San Joaquin Valley. It was anticipated that the offspring of these insects would fly into table grape vineyards and spread Xylella fastidiosa, an endemic species of bacteria known as the cause of Pierce’s Disease, for which there is no cure. Panicked growers feared a local repeat of the devastating losses seen in the Temecula Valley a few years earlier, after sharpshooters were introduced.

In response to this threat, local public and private organizations snapped into action and developed the General Beale Pilot Project. On display within this 50 square mile project was a coordinated effort at integrated pest management involving local growers, their pest control advisors, commodity organizations, universities, and government agencies at the local, state, and federal levels. The challenges and successes of this two-decade effort are summarized as a case study published last week in the Entomological Society of America’s open-access Journal of Integrated Pest Management.

At the core of the project was the USDA Area Wide Treatment Program that utilized public funds for citrus growers to do coordinated treatments for overwintering sharpshooters in their groves, based on captures from traps serviced weekly by the California Department of Food and Agriculture. Making these treatments was not an easy sale, especially when considering that treatments to citrus were voluntary, provided minimal benefit to the citrus grower making the application, and had the potential to disrupt natural enemies utilized for biological control.

Pierce’s disease surveys were conducted by the University of California every August and September when visual symptoms were at their peak, including scorched leaves and persistent petioles. Vines positive for Pierce’s disease were marked and removed during the fall or winter.(Image originally published in Haviland et al 2021, Journal of Integrated Pest Management)

The California Department of Food and Agriculture Pierce’s Disease Control Program has monitored for glassy-winged sharpshooters by deploying a grid of over 450 traps, such as the one shown here, checked every one to two weeks since 2001. (Image originally published in Haviland et al 2021, Journal of Integrated Pest Management)

The grape growers that produced the more than 3,000 acres of table grapes in the project also took great care to control sharpshooters in their vineyards while providing access to University of California surveyors responsible for identifying infected vines. These survey efforts were funded directly by table grape growers who, following disease confirmation, were responsible for completely removing infected vines.

The General Beale Pilot Project has now been in place for nearly 20 years. Voluntary citrus grower cooperation with treatment programs has been nearly universal. Grape growers made their treatments annually, removed infected vines, and in some cases removed entire vineyards. County, state, and federal organizations worked together alongside farmers, industry-based organizations, and the University of California to achieve success, including an all-time low for disease incidence during the most recent surveys, which were conducted in the fall of 2020.

The General Beale Pilot Project serves as a great example of integrated pest management of a complicated vector-borne disease. Throughout its history, the project had periods of great success, but also faced significant challenges associated with insecticide resistance, untreatable refuges, inconsistency in funding, and disease epidemiology.

David Haviland is an entomology and pest management farm advisor with the University of California Cooperative Extension’s Kern County office in Bakersfield, California. Email: dhaviland@ucdavis.edu.