As the table grape harvest hits the home stretch in many San Joaquin Valley vineyards, growers are urged to keep an eye out for infestations of the vine mealybug, the crop’s most significant pest.

During harvest, vineyard owners or managers should continue monitoring for the bug on fruit and foliage, and educate harvest crews to recognize infestations and report them, if found, a University of California pest management website advises.

During post-harvest activities, growers should continue monitoring for mealybugs on fruit and foliage and treat, if needed. If the vine mealybug is present, steam-sanitize equipment before moving to uninfested areas.

Vine mealybugs — Planococcus ficus — are small, soft, oval and flat, and are covered with a white, mealy wax that extends into spines, according to the UC Statewide Integrated Pest Management Program. All or most life stages of the pest can be present year-round on a vine, depending on the region. The vine mealybug appears in all of California’s major production areas. 

HONEYDEW LEADS TO MOLD

Damage is similar to that of other grape-infesting mealybugs, in that it produces honeydew that drops onto the bunches and other vine parts, and can lead to black, sooty mold. In fact, a vine with large numbers of the pest can have so much honeydew that it looks like candle wax.

Extension Viticulture Advisor Asraf El-kereamy said earlier this year that the pest not only renders table grapes unmarketable because of the honeydew left behind, but it is also known also to vector grapevine leafroll virus.

Ants can compound management issues as they feed on the honeydew, and can become protective of mealybugs, which can have a negative impact on parasitoid populations that could otherwise help integrated pest management control of the mealybug.

Several different species of mealybugs can infest grapevines, and the UC cautions that management techniques for the species differ. That means growers should know which species of mealybug is present.

This can be done by collecting the largest mealybugs, putting them in a jar of alcohol or a sealed plastic bag, and taking the sample to a UC Cooperative Extension farm advisor or county agricultural commission.

CONTROLLING THE PEST

Mating disruption to control vine mealybugs in table grapes is showing promise in UC studies. Research trials by UCCE Entomologist David Haviland show that sprayable formulations of pheromone have improved performance over a costlier dispenser-based system that was used previously.

Mating disruption inundates vineyards with artificial vine mealybug pheromone, hindering males’ ability to actually find females, and thus reducing reproduction, Haviland reports in a recent paper. Mating disruption with products such as CheckMate VMB-F at 30-day intervals had a significant impact, while applying pheromone at 45-day intervals didn’t effectively disrupt mating.

Among biological controls, two have been imported and released in California. The more successful is Anagyrus pseudococci, which has provided up to 90 percent parasitism of exposed mealybugs late in the season in the San Joaquin Valley, according to UC IPM. They’re effective at catching vine mealybugs before they return to the roots or lower trunk to overwinter.

CULTURAL CONTROL PRACTICES

As for cultural controls, female and nymphal mealybugs don’t fly, so they must be carried by humans, equipment, wind, or birds, or be present on vines at planting, the university notes. Thus, growers should make sure equipment, vines, grapes, or winery waste don’t go near uninfested vineyards.

Further, growers can reduce cluster infestation by pruning vines to prevent clusters hanging directly on the cordon, the UC IPM advises. In areas where mealybugs overwinter in roots, growers can slow the bugs from moving up the vines in the spring by applying Tanglefoot bands onto duct tape and wrapping it around the trunk with the bark removed.

For the UC IPM’s complete instructions in managing the vine mealybug, including detailed advice on monitoring, visit https://bit.ly/2PWT0Cp