As the vine mealybug (VMB) continues to threaten California vineyards, disciplined use of the several available insecticide alternatives has emerged as the primary element in management of the pest.
Walter Bentley, University of California IPM entomologist at the Kearney Agricultural Center, Parlier, speaking at the San Joaquin Valley Grape Symposium at Easton, reported on his recent research with those materials and offered some tips for growers.
While advances have been made in biological control and mating disruption of VMB for organic vineyards, he said a wide range of relatively effective insecticides and a good supply of information for using them in conventional vineyards are now available.
“But,” he added, “the right timing and placement of these products are extremely important, and there are mistakes being made.”
VMB, an exotic, invasive pest from the Mediterranean region, showed up in the Coachella Valley in the early 1980s and was for several years thought to be grape mealybug, which it resembles. Closer investigation, however, showed the two to be separate species. In the years since, VMB has become known as the state’s most serious arthropod pest in vineyards.
Its obvious damage to vines and fruit is characteristic waxy deposits of honeydew, which lead to sooty mold and fruit damage. Of particular importance to raisin and wine grape growers in the SJV is its transmission of leafroll virus that causes uneven ripening of grapes.
In most parts of the state, various life stages of VMB are found during the winter under the bark, in developing buds, and on roots. As temperatures warm in the spring, it moves throughout the vine and roots.
Using Lorsban and Applaud as examples, Bentley made some comparisons. Lorsban, a contact material, might be preferred by table grape growers who are also concerned with spiders, although it would not be suitable for use near a populated area or waterway, where the growth regulator Applaud would be the choice. Applaud is most effective on the crawler stage, the weak link in the VMB life cycle.
The key to control with Lorsban or Applaud, he pointed out, is to time treatments (as directed by label) when crawler stages are moving from a protected area out into a less hidden area.
“The efficacy of an insecticide is dependent on the structure of the vine,” he said. Old, gnarled vines are more difficult to treat than younger vines.
On the North Coast, however, an “Air Spade” is used to blow off bark and expose the crawlers, which are then more vulnerable to insecticides, as well as parasites.
“The important thing is to look for basal leaves that appear in April or May. If you use Applaud, treat in late April or early May as the crawlers move from the wood to the leaves. Don’t wait until June when the crawlers have become adults.”
Bentley’s recent studies focused on insecticides having short reentry intervals and greater worker safety. When applied at the correct rates and proper timing, they provide control on par with Lorsban and Lannate.
Two of them, Admire Pro and Platinum, are neonicotinoid systemics applied by drip and care must be taken to avoid insect resistance. Both performed best when applied in late April or May.
“One of the big mistakes I see,” Bentley stressed, “is PCAs recommending Admire for flood irrigation. It just does not work. After researching Admire with flood irrigation four or five times, our results have been the same.”
He said Applaud can be rotated with the new tetramic acid systemic, Movento, to control the immature stages during the above period. Since they have different modes of action, rotating them prevents resistance in VMB. His 2007 trials showed that a single treatment with 8 ounces of Movento was equal to two 12-ounce applications of Applaud.
“If on a drip irrigation system,” he said, “either Admire or Platinum, but not both, could be utilized in a rotation with both Applaud and Movento.”
Movento, he explained, when sprayed on leaves is absorbed by the phloem, where VMB feeds, and taken throughout the vine. His preliminary test results show that an application of Movento made in June provides greater residual control than one made in May.
Two other neonicotinoids were evaluated during his 2008 trials. He found that Assail at 2 ounces per acre, twice the registered rate, gave a quick kill of VMB while Clutch also gave a quick kill, but did not provide residual control.
Bentley warned that heading off resistance in VMB, like avoiding resistance in powdery mildew, depends on rotating materials with different modes of action. “If resistance to these insecticides develops, grape growers will no longer be able to manage VMB.”
Complete details for managing VMB, revised to October 2008, are available at the University of California IPM Web site, http://www.ipm.ucdavis.edu.
The symposium also heard from Dong Wang, soil scientist, USDA-ARS, Parlier, who reported on research during 2007 and 2008 on vineyard soil fumigation alternatives to methyl bromide. The project, designed to find information for vineyard replants, will continue into 2011.
Once used extensively to fumigate vineyards, orchards, and other cropland to control soilborne pests and weeds, methyl bromide is now classified as an ozone-depleting material. Its use is restricted while alternatives are being evaluated.
Wang and his fellow researchers investigated shank-applied Telone C35 and the similar In-Line fumigant applied by drip irrigation in grape plots at the USDA Parlier station and a commercial vineyard near Fresno.
Treatments with methyl bromide, a cover crop of white mustard, and an untreated portion were also used for comparison. Following fumigant applications, tarps of high-density polyethylene film (HDPE) and virtually impermeable film (VIF) were placed over treated areas to prevent gasses from escaping into the atmosphere.
Later, the scientists evaluated effects on nematodes, fungi, and weeds in the top 6 inches of treated soil.
Among findings thus far, Wang said they learned that both alternative fumigants, at rates of about 25 gallons per acre, gave very effective nematode control.
About 85 percent of shank-injected fumigant escaped from un-tarped plots, but only 18 percent was lost with the VIF tarp in place.
The treatment with a cover crop of white mustard showed mixed results and was not conclusive.
As the project continues this year, Wang said, “We will be exploring lower rates of fumigants and testing new VIF tarps from several manufacturers. We will also be measuring the growth responses of the vines. We plan to expand the number of grower demonstration plots to show the practical side of the project.”