What is in this article?:
- Vine mealybug infestations continue to increase in northern San Joaquin Valley vineyards, and their presence has led to greater reliance on insecticides and disruption of successful IPM programs.
- Although more vineyards are becoming infested, populations within infested areas are declining because the judicious use of insecticides has successfully lowered mealybug populations in areas that are infested.
In research led by Kent Daane over the past few years in the San Joaquin Valley, mating disruption significantly reduced pheromone trap catches. However, traps were not “shut down”, as often happens with moth insects, probably because of the large number of mealybug males in the vineyard and their poor flight, which may result in males blown by the wind near the pheromone traps and then moving into the trap once in the vicinity. Also, in some trials there was a late summer increase in males caught, suggesting that more work still needs to be done to increase the longevity of dispensers that are currently available.
The effectiveness of mating disruption likely depends on many factors, including pest density. In areas with very low mealybug density male mealybugs most likely require the use of pheromones to locate the females. However, when pest densities are high the reliance on pheromones is likely negligible for a male that only needs to walk a centimeter to find a mate. Due to the fact that mealybug distribution is highly clumped in most vineyards (lots of vines with no mealybugs and a few vines with lots of mealybugs), mating disruption is an option that can be included as part of a mealybug management program, but that is unlikely to ever become a stand-alone option for control. To date, the most successful uses of mating disruption have been to use chemical control to clean up a vineyard, and then use mating disruption in combination with other insecticides for long-term maintenance. However, mating disruption has not gained in the widespread acceptance because of high cost and the continued need for insecticide treatments.
Season-long control programs for vine mealybug are typically comprised of a combination of insecticide treatments assisted by biological control. Possible insecticide options include Lorsban as a delayed-dormant application to the trunk just before bud break, one or two applications of Applaud in the spring when crawlers are moving up the trunk, soil applications of neonicotinoids during bloom, applications of Movento from April through June, and late-season foliar sprays of contact materials like Clutch or Assail. Management programs for wine grapes in the San Joaquin Valley typically include one to three of these options in any given year.
Lorsban and other generic products containing chlorpyrifos can be applied as delayed-dormant or postharvest treatments that also can help control ants. The delayed dormant treatment occurs when most of the mealybug population is still below ground under the bark, and the young are killed as they move up the vine in the spring; control levels have been reported as high as 90 percent of the population.
In five field studies conducted by Haviland in Kern County table grapes from 2008 to 2011 delayed-dormant applications of Lorsban provided an average reduction of 46.3 percent in the number of mealybugs per vine during three-minute timed searches in June and a 69.2 percent reduction in the percentages of clusters with honeydew or mealybugs in July.
As a postharvest application, Lorsban has been used to kill mealybugs before they are able to return below ground for the winter. This practice has been used for several years, but is becoming less common. This is because recent research in Kern County has shown that post-harvest treatments with Lorsban are not effective, label changes now mandate only one application of Lorsban per season (making delayed-dormant treatments a much better option that postharvest treatments), and because of concerns that this timing may severely impact beneficials, especially parasitoids, which are in the period of highest densities in late summer.