University of California Integrated Pest Management Specialist Walt Bentley suggests growers offer a reward to fieldworkers if they find vine mealybug for the first time in a vineyard.
This may sound like an unorthodox recommendation coming from a respected pest management specialist like Bentley, but the entomologist stationed at the UC Kearney Ag Center says it behooves growers and pest control advisers (PCA) to pull out all the stops to halt a pest from becoming established in a vineyard that cost a North Coast premium wine grape grower $1,000 per acre to eradicate, according to Bentley's colleague Kent M. Daane, UC Cooperative Extension insect biology specialist.
Considering the vine mealybug can destroy a crop, a worker bonus is certainly worth budgeting for to gain added eyes to be on the look out for early signs of one of the most destructive pests ever to invade California vineyards.
Bentley told a group of veteran pest control advisers at a tree and vine pest management seminar sponsored by Bayer CropScience recently in Monterey he is fearful smaller growers, especially San Joaquin Valley raisin producers, do not correctly identify the vine mealybug or are missing it altogether. This guarantees establishment and spread.
“It is so much easier and less expensive to control vine mealybug early if it gets into a vineyard. Once it is widespread, you cannot go without treating the entire vineyard,” he said.
Bentley said SJV growers need to look not only for the vine mealybug on the top of basal leaves, but look for signs of the vine mealybug such as leaves dropped beneath the vine covered with honeydew. On the coast, vine mealybug is normally found on the underside of leaves.
“They appear as white speckling on the leaves,” said Bentley, noting that vine mealybug can be introduced into a vineyard on equipment or rodents and birds can spread it. It also can be introduced on nursery stock.
There also are effective pheromone traps to monitor for vine mealybug.
Since it was first discovered in California in 1994, it has spread to most grape producing areas.
Vine mealybug, which overwinters on roots and trunks, has several biological attributes that result in a rapid increase in its density. Females can deposit more than 500 eggs. In the San Joaquin Valley, there are four to seven generations per year as compared with two or three for the grape mealybug. This creates overlapping generations and higher populations. Individual vine mealybugs excrete far more honeydew than grape mealybug resulting in excessive sooty mold growth on grapes and leaves.
Second, vine mealybug can feed on all parts of the vine throughout the year, with a majority of the overwintering population located underneath the bark of the trunk or underground on the roots. This makes it difficult to control with foliar sprays. However, Bentley said vine mealybug crawlers are active in the early spring when temperatures reaches 55 to 60 degrees. “This is where products like Lorsban and Applaud in a delayed dormant sprays work well,” he said.
These foliar pesticides can control young vine mealybug growth stages. However, once the vine mealybug becomes established, it requires an application of the systemic pesticide Admire to control the pest because the insecticide is taken up into the vine and reaches mealybugs hidden within the bark where foliar sprays cannot touch.
Admire can also be shanked into berms and irrigated in, but the soil must remain wet for uptake. Some growers have used Admire on individual vines to control initial infestations.
Applying the systemic pesticide through drip irrigation works best, added Bentley. “Thirty-two ounces of Admire in late April after bud break works well,” said Bentley.
However, Bentley cautioned San Joaquin Valley growers using deficit irrigation to improve wine grape quality that it requires plenty of water for efficient uptake of Admire and deficit irrigation may not provide that.
Ants guard mealybug
One of the most intriguing aspects of vine mealybug is that it has a protector, especially in coastal vineyard. It is the Argentine ant. It thrives on vine mealybug honeydew and protects the pest from predators.
Get rid of the ants and you can reduce vine mealybug damage. That is what Daane, Bentley and University California, Riverside urban entomologist and ant specialist Mike Rust have been working on.
Foliar treatments for ants could be expensive and disruptive to the sustainable farming movement in coastal vineyards.
Therefore, the three entomologists have been focusing on insecticide-sugar bait to attract worker ants that would take the insecticide back to the colony and feed the sugar bait to larvae, thus breaking the reproduction cycle. The baits Daane has successfully used are either imidacloprid in a product called Preempt, the same active ingredient in Provado and Admire, or spinosad.
The concept has proven to work well, said Daane. However until now it has required a high number of bait stations and high labor costs to refill them.
Daane said the trio has developed a three-quart, partially buried bait station that has worked to attract ants when there are five stations per acre and the station is destined for commercialization.
“And they are filled just once a year,” said Daane.
“After just one year we have seen positive results in the form of lower cluster damage from vine mealybug,” Daane told the PCAs at the tree and vine seminar.
Based on the five stations per acre, Daane said it will take several seasons to reduce the ant population to levels that vine mealybug will not pose a major problem.
Closer to bait
“What we will see is the colonies move closer to the bait each year” and that will attract and kill more ants, said Daane, who said ants range about 20 meters away from their colonies.
Placement of the bait stations is critical. Daane said ants migrate into vineyards from riparian areas. “April seems to be the best time to get the stations out in coastal vineyards,” added the entomologist.
Daane expects commercialization of the sugar bait-pesticide attractant in 2007 or 2008. Cost will be about $70 per acre.
Daane added that Rust is working on developing the same attractant bait concept in citrus.