The topic of discussion involved “Pests to Watch For” in the vineyards.

In the case of the University of California Cooperative Extension specialist who spoke on that subject, it was a matter of the pest already in evidence where eradication efforts have been less than successful.  In the case of his audience, it was grape growers in the state of Washington who are trying to keep the pest out of their fields.

“We first found vine mealybugs in Coachella Valley in the early 1990s before they spread to Central Valley (Kern County) in the late 1990s followed by Fresno County and then exploded through much of the state in the early 2000s,” said Kent Daane of UC Berkeley, a 30-year veteran of keeping an eye on Planococcus ficus as it became one of California’s most significant vineyard pests with grapevines its preferred host.

“Vine mealybug is far worse than grape mealybug as it lays more eggs, produces more generations, leaves more honeydew excretions, and feeds more readily on grape leaves as a vector for a number of diseases,” he said. “A variety of eradication efforts were tried in both Napa and Sonoma counties, but were unsuccessful and the pest has now spread into Oregon.”

In the first of a series of webinars on “Pests Not Currently in Washington State” and focusing on tools to combat and management practices to institute if/when they arrive, Washington State University Viticulture, the Washington Wine Industry Foundation, and the WSDA Specialty Crop Block Grant program presented the Zoom meeting to help understand the pests migration and why vine mealybug was more destructive than the common species already in Washington, like grape/obscure/longtailed mealybug.

Acknowledging that “my whole goal is to scare you and I hope I do so,” Daane did admit that, “If they can’t be eradicated, it’s not the end of the world.

An invasive species

“VMB is an invasive species found in many parts of the world with the West Coast version probably arriving via Mexico,” Daane said. “Traditional eradication efforts in California haven’t been less than totally successful and vine mealybug will be difficult to eradicate if it arrives in Washington, but once you get it and you can’t make it go away completely, you learn how to live with it.”

Initial conjecture some 20 years ago was that the source of movement for the infestations could be blamed on infested nursery plant materials.

Fellow farm advisor, entomologist David Haviland, wrote that, “Seasonality of VMB populations varies with vine phenology and geographical area with populations peaking during late spring in Coachella Valley, but hitting the high mark in the San Joaquin Valley closer to July.  VMB has up to six generations per year that result in multiple life stages at any given time over the season,” he wrote.

“It’s high reproductive rate and rapid development times promote severe infestations that are difficult to control,” added UC Riverside extension specialist Matt Daugherty.

“Indeed,” agreed Daane. “While the grape mealybug produces 90-120 eggs per cycle, the vine mealybug is responsible for more generations via 125-220 eggs.”

Use of pheromones and mating disruption help mitigate the problem — and add to the cost of the pest management battle. Field saturation, between 35-100 dispensers per acre, is recommended as is repeated use of sprays. “In California, growers lay down 5-6 sprays a season at a cost of $120 per acre.

“If vine mealybug is found in Washington, growers will need to utilize good chemical controls and work together cooperatively to fight it.”