Tools to control vine mealybug (VMB) in individual vineyards are available to California grape growers, but the key to stopping its further spread is early detection of infestations, particularly at harvesttime.
That's the take-home message from Walt Bentley, University of California Extension entomologist at the Kearney Research and Education Center, Parlier.
During a recent field day at KREC, Bentley sketched results of studies done in 2002 by a group of researchers he heads. “Early detection,” he said, “is essential in keeping this pest out of your vineyard. Listen to the people who see every vine in the vineyard — either harvest workers or irrigators. Then go out and take a close look yourself.
“When you have a few vines to deal with, it is relatively easy to stop. When you have a whole vineyard infested, it's a different story. Once it is widespread, like it is in the Del Rey area of Fresno County, it is very difficult to manage.”
Now in a dozen California counties from the North Coast to the Central Coast and into the San Joaquin Valley, VMB, or Planococcus ficus, showed up in the Coachella Valley in 1994 and in several SJV districts by 1998.
Can spread unnoticed
It sucks the phloem from vines and attacks any variety. Infested vines have poor bud development the following season and losses can reach 30 percent. Often an infestation starts in a corner of a vineyard and spreads before the grower notices it.
An exotic pest distinct from the common, native grape mealybug (GMB), which goes mainly to trunks, spurs, and clusters, VMB can be found throughout the vine, including the roots, making it much more destructive and difficult to control. Although frost will kill exposed VMB, those underground on roots survive.
VMB excretes large volumes of honeydew, which form whitish crystals on vine parts and attract sooty mold growth that in turns damages the fruit.
One sign of VMB activity in early June is the adults of the pest, seen as tiny white flecks, on the top of leaves. (GMB tend to remain on the undersides of leaves.) Another is crystalized honeydew deposits on leaves and canes. Later the debris appears on clusters at veraison.
Yet another indicator is activity by several species of ants carrying VMB around on the vines, feeding on the honeydew, and fending off natural enemies.
Among the quick ways to identify VMB itself is its smaller size and smaller tail structure compared with the several other mealybug species that go to grapes. VMB, however, closely resembles citrus mealybug and samples may need expert identification.
The UC publication, Mealybugs in California Vineyards, has diagrams and photos to aid in distinguishing the several species, and ag commissioners in affected counties are cooperating in identification efforts.
Eradicate or manage
By selecting from several chemicals available, Bentley said, growers can eradicate or manage it, “at least in the short term.”
“The issue of resistance does come up because VMB does not fly from one area to another and the same population is exposed when the same type of pesticide is used again. We hope that other studies will allow us to manage it with some biological control.”
As an eradication practice on young vines, the neonicotinoid systemic, Admire, was applied through drip lines either as a single treatment in May or in split applications in May and June.
However, he cautioned, “Admire is carried by the xylem, the water-carrying tissue, and mealybugs feed on the phloem, so we don't get good control on woody parts where those two organs are separated. But once in the canes and leaves, the Admire really kicks in.”
So, he explained, Admire may not totally eradicate VMB on older vines, although it will reduce a population. Admire is not suited to flood irrigation because of costs. Another similar systemic in the trials, Platinum, moves more easily into the root zone but is unregistered.
For the management approach on established vines, Bentley said contact spray treatments with Lorsban are effective when both VMB and GMB crawlers emerge from the bark and move from the crown of the vine toward spurs during temperatures around 60 degrees during the spring, or perhaps in February.
Other foliar-applied, contact materials, including Danitol, Dimethoate, and Lannate, provided fast-kill activity, while the insect-growth regulator Applaud also reduced VMB crawlers. Counts of live crawlers during July of 2002, averaging 27.5 per leaf in the untreated check, ranged from 3.3 per leaf with Lannate to 10.8 with Applaud.
Field sanitation is important in avoiding VMB, and Bentley said all equipment - harvesters, mechanical pruners, and rotary movers - operating in an infested vineyard can spread the pest. Machinery working in an infested vineyard should be steam cleaned or washed with a 2 percent chlorine solution before using it in a clean vineyard.
Humans, too, can be carriers of VMB and unnecessary entry into an infested vineyard should be avoided. Contaminated clothing should be washed before being worn in a clean vineyard.
“Don't be afraid to talk to your neighbors about this pest,” said Bentley. “You may be hesitant about saying something but if you suspect they have an infestation, tell them. This is one thing you've got to tell them. If it gets out of control it can cost you big bucks.”
Only partial success has been reached thus far with biological control of VMB with releases of tiny wasp parasites. They have been able to reach a survival of 80 to 90 percent. That's because the parasites' activity lags behind development of VMB and sufficient wasp populations do not occur until after vines have become infested.