Left unchecked, vine mealybug can cause yield losses in wine grapes across a broad range of growing conditions. In many vineyards, the pest’s a fact of life; eradicating it completely is extremely difficult. Fortunately, vigilant scouting, a range of control products and the right management program and guidance can help prevent it from causing economic losses.

Different ways vine mealybug hits a grape crop

Vine mealybug is a season-long problem requiring scouting by a PCA early in the season. The pest can cause economic damage to wine grape plants and fruit in several ways. First, it feeds on trunks and stems, pulling sugars that are later excreted as a honeydew that promotes the development of black sooty mold. Those excretions also attract other insect pests like ants. Finally, the pest can vector viruses, some that can be potentially fatal.

When hampered by vine mealybug damage, a vine becomes more susceptible to other crop diseases, some of which are viral. And when plants are infected with more than one disease, it can cause sudden vine collapse and plant death.

The influence of weather and growing conditions

How early vine mealybug begins damaging plants depends on the specific weather conditions and how they influence the bug’s ability to overwinter and establish an early first generation, according to Matthew Ehlhardt with the Grow West Technical Service team. Vine mealybugs can overwinter under vine bark, along a plant’s trunk and even in root systems. This makes them next-to-impossible to eradicate and escalates potential losses.

“Where we’re warmer and drier, they could be popping their ugly heads out earlier this year,” Ehlhardt said. “That necessitates our PCAs to be on top of scouting early and identifying any potential problem areas.”

The size and layout of vineyards also has a lot to do with the development of vine mealybug pressures. Larger adjoining vineyards that comprise more of a large-scale monoculture system are more likely to face vine mealybug pressures.

“In the Valley, it’s a totally different growing environment compared to the coastal areas as far as the layout of the vineyards. We have bigger acreages and they’re more contiguous in the Valley,” said Grow West Technical Service Manager Layne Wade. “There are vineyards packed next to each other in some areas versus being separated by hills. In those situations, the pest can move and spread much easier from block to block creating more of an infestation environment.

Vine mealybug treatment options

Sandy Valera is one of the PCAs responsible for diagnosing vine mealybug pressures in the North Coast region. Growing conditions there are different than other Grow West regions; temperatures are normally cooler, meaning fewer vine mealybug generations each year. Whereas there are normally between four and six generations further inland, growers in coastal areas like Sonoma County are more likely to see between two and three each year. Farther south where temperatures are higher year-round, it’s not uncommon to see up to 12 generations each year.

“You can’t be complacent with vine mealybug. You have to be vigilant and aware because if it starts small, it’s not going to stay small,” Valera said. “Being aggressive in mitigating damage will save you in the long run. But if you ignore it, it will be harder to manage in the end. Thankfully, the tools we have will fit into standard spray programs.”

Those tools comprise multiple product types and modes of action to manage the pest including:

• Soil-applied neonicitinoid insecticides
• Foliar-applied insecticides
• Insect growth regulators
• Pheromone mating disruptors

“Growers who don’t have severe populations or infestations may get away with mating disruptions,” Ehlhardt said. “It’s best to not rely on one tool alone and put all your eggs in one basket. Pheromones and disruptors don’t eliminate a population but can bring it down.”

Consider these other factors in controlling vine mealybug

Cost, equipment, labor and regulation contribute to the most effective, practical solution, Valera added. “The solutions must be economically viable,” she said. “While labor is the biggest issue with a lot of treatments, there’s a growing problem going forward in how California is going to regulate neonicitinoid pesticides. That’s going to impact our ability to rotate chemistries effectively.”

Communication and having the right team and partners in place are fundamental to ensuring vine mealybug doesn’t reach economic damage thresholds. While that team includes informed PCAs, it also calls for a “neighborhood watch” approach, Valera said. This sort of collective strategy is about more than monitoring, though, Wade added. Applying pheromone products in large areas contributes to minimal vine mealybug damage over long periods of time. But it must be cost-effective.

“The longer you use pheromones, the greater the effect on the population. But it’s often an economics-driven decision and not necessarily a necessity in every vineyard,” Wade said. “Some groups are trying to encourage all growers in a region to adopt pheromone disruption, because you minimize the infestation potential from the beginning. Then from a PCA’s standpoint, we can add insecticides on top of that region-wide pheromone control for broader, vineyard-specific control. The pheromone becomes the foundation of a more comprehensive approach.”

Communication is key to effective control

Regardless of the specific combination of controls you use to manage vine mealybug, the team you employ to manage the pest across your acres is a major component of a successful strategy. Valera emphasized communication between a grower and PCA as being another major part of the foundation of effective control.

“Grow West has a communication style that is very different from other companies. There aren’t a lot of cards held close to the chest. It’s an open, free exchange of ideas,” she said. “It’s really important to develop a strong rapport between scouts, PCAs and growers so everyone knows what’s working and what’s not working. We bring that to the table at Grow West.”

Talk to your Grow West PCA if you want to explore options for knocking down vine mealybug on your operation.

 

Header image provided by Statewide IPM Program, University of California Agriculture and Natural Resources.