Hammering vine mealybug with harsh, quick knockdown materials is not going to be the answer for grape growers struggling to control the spreading pest.
Sustainable and integrated approaches will be critical to future management programs. Researchers are now working with mating disruption strategies.
Lorsban, in particular, is under scrutiny by the California Department of Pesticide Regulation. The product has been registered under a Section 18 for the past eight years for mealybug control. Originally intended for grape mealybug control, growers quickly began relying on it for vine mealybug control when that pest arrived in the state. The net result has been an increase in use, rather than a decrease.
“DPR is looking at these products and Section 18s and how they are really being used,” says Kent Daane, University of California entomologist at the Kearney Agricultural Center in Parlier, Calif. Daane was addressing attendees at the first stop of UC's Central Coast Research Roadshow in Paso Robles, Calif. The series of summer Roadshows are being sponsored in part by the American Vineyard Foundation (AVF) to present the latest in grape research directly to growers, winemakers and allied industry. The four regional meetings feature research that has been funded by the AVF, Viticulture Consortium West (VCW), and the California Competitive Grant Program for Research in Viticulture and Enology (CCGPVE). Jerry Lohr, owner of J. Lohr Vineyards headquartered in San Jose helped underwrite the cost. “We have to use Lorsban judiciously to keep that product available for the longest period of time. It's one of the best products to knock down that population quickly.”
Softer materials are being passed over by growers looking for quick control of vine mealybug. Often, it's a frustration regarding how they work and a misunderstanding of the various factors that impact performance.
“Some growers swear by Admire, others by Venom,” Daane says. “It has to do with the vine, soil conditions, and irrigation. In Fresno, we don't get a lot of rain and the root system is not spread out. Admire is fantastic under those conditions. However, in the Paso Robles area on heavier clay soils, Admire tends to bind up in the upper root zone and won't get picked up as easily by the vine, so Venom tends to be better.”
Daane said vine mealybug will not be eradicated, but “we can slow it down. The key is to hit it hard when it first comes in.”
Vine mealybug has multiple generations per year. Once it gets established in a vineyard every growth stage will be in the vineyards season long.
Parasitism is a promising cultural control that may boost the overall success of management efforts. UC researchers are looking at new species of parasites that could be used to manage vine mealybug. However, the ant in the ointment is the Argentine ant.
“They disrupt biocontrol,” Daane says. “If you want to improve biocontrol you have to kill the ants. To kill the ants you have to use Lorsban. If you're trying to implement a sustainable program you have to move away from Lorsban.”
It's a “Catch-22” situation at the very least. However, researchers are zeroing in on a management strategy that just might help growers reduce mealybugs through “softer” strategies and ultimately reduce dependence on harsher materials. The use of ant bait is one component, while parasitoids are another.
“Parasitoids on their own do not get the mealybugs under the bark,” Daane says. “They do a so-so job and then leave looking for easier prey somewhere else.”
However, researchers have found that placing plastic dispensers in the field that contain a vine mealybug pheromone not only disrupts mating, but also increases parasitism. As an added bonus, it shifts the female to male ratio, reducing the males that exist in subsequent generations.
A portion of the increased parasitism is attributed to the use of softer chemical controls, but the results have been encouraging. Even when Applaud and Admire were used in the trials to control initial mealybug populations, the use of mating disruption in combination with parasitism was pronounced.
“Our hypothesis is the parasite is out there on that vine,” Daane says. “It's about to take off, but it smells the pheromone and thinks there is a mealybug somewhere close by. That instigates a greater searching behavior. It spends more time in the vineyard rooting around under the bark to find those mealybugs.”
The dispensers containing the pheromone for mating disruption cost about $130 an acre. “We think this can work,” Daane says. “We just have to get the price down to a reasonable level for the ant control and mating disruption portion of the equation.”
The bottom line to keep in mind is the strategy is only effective at low starting populations. “You can't use it to bring a population down,” Daane says. “If you have a lot of mealybugs out there, you've got to use an insecticide to knock down the population initially.” Once that is achieved, biocontrol measures can be implemented with a greater degree of success.