Careful detective work by a team of University of California Cooperative Extension scientists allows California grape farmers to rest assured newly planted grapevines are free of vine mealybug.

Vine mealybug was first identified in California in 1994. It has since spread to scattered vineyards throughout California's wine-, table- and raisin-grape-growing regions. As the vine mealybug feeds on vines and grape stems, it reduces grapevine vitality, transmits grape viruses and produces tremendous amounts of sticky honeydew, promoting sooty mold that renders the grapes inedible.

Once a vineyard is infested, vine mealybug can only be controlled with insecticides.

“If this insect becomes widespread, insecticide use in vineyards will increase, and that disrupts biological control programs being implemented for other pests in California's vineyards,” said Walt Bentley, UC Integrated Pest Management advisor, based at the UC Kearney Research and Extension Center near Parlier. “With many grape farmers already struggling financially, being forced to use a costly insecticide could put them out of business.”

Because of this serious threat, the UC Integrated Pest Management Program supplied a $15,000 grant and assembled a team to develop new methods to detect and manage the vine mealybug. The team, coordinated by Bentley, includes Kent Daane, Cooperative Extension entomologist; Lucia Varela and Jim Stapleton, UC IPM advisors; David Haviland, Kern County IPM advisor; and farm advisors Rhonda Smith of Sonoma County, Jennifer Hashim of Kern County and Stephen Vasquez of Fresno County.

Age as indication

The scientists' first clue to understanding the pest's rapid spread, Bentley said, was the relative young age of infested vineyards.

“Normally, with a pest like vine mealybug, which doesn't move much, infestation is associated with older plantings. But we were finding it on younger plantings, which told us it wasn't being moved as you would normally expect,” Bentley said.

The team visited infested vineyards and questioned grape growers. They learned infestations were most common on vines planted within the last four to five years. That finding led them to nurseries that supply cuttings to grape farmers. The nurseries, recognizing their role in vine mealybug control, were interested in a treatment for vine mealybug that would not expose their fieldworkers to toxic chemicals.

Using a method that has been successful in controlling other pests, Bentley and his colleagues conducted experiments with vine mealybug-infested grape cuttings. They found that immersing grape cuttings in 125-degree water for five minutes kills 99.99 percent of all life stages of vine mealybug without damaging the vines.

In less than 12 months, UC scientists solved the mystery and validated a treatment protocol for grapevine nurseries. Nursery staff now treat their planting stock by immersing materials for five minutes each into each of three tanks: a warming tank, a treatment tank of water above 125 degrees and then a cooling tank. Four providers of dormant grape nursery stock have already begun implementing this technique to ensure their planting material is free of vine mealybug.

Water treatment

The scientists are now actively taking the new information out to the field and conducting other programs to limit the spread of vine mealybug. They suggest farmers be sure the nurseries where they buy new grape cuttings are using the hot-water treatment. In addition, farmers should take great care to avoid movement of the pest in equipment and workers' clothing from infested vineyards into clean vineyards, especially during harvest, which offers the greatest opportunities for spread of the pest.

Bentley recommends that farmers carefully monitor vineyards and call the local UC Cooperative Extension office or the agricultural commissioner's office immediately for confirmation of a suspected vine mealybug infestation.