Mealybugs can act as vectors for grape leafroll associated virus. They overwinter as immatures (called crawlers), develop into adults that lay eggs and these eggs hatch to produce the next generation of mealybugs. While virus-bearing mealybugs don't fly, the small crawlers can be spread by wind. Julie Lupia, an undergraduate student in the Oeonology and Viticulture program at Brock University, is tracking the development of mealybugs in commercial vineyards in Niagara as part of her undergraduate thesis project. She works with my team of summer students to examine 10 vines in each of 4 commercial vineyards by peeling back the bark and looking for eggs, crawlers or adults twice a week. We are also surveying a cross-section of vineyards in Niagara, southwestern Ontario and Prince Edward County, visiting them once during the summer to determine the incidence of mealybugs (and scale insects that can also carry the virus).
The new generation of mealybug crawlers started hatching last week in Niagara. The figure below shows the size of these insects -- look for the fuzzy white mass (the adult female that died after laying eggs) and tiny pinkish-brown, rice-shaped insects clustered around it. You can see how small they are relative to the bark to the left of the photo so a hand lens or magnifying glass may be necessary.
Photo credit Julie Lupia
This is the optimum time to apply insecticides to try to reduce spread of leafroll virus in your vineyard by mealybugs: the insecticides work best on earlier mobile growth stages of mealybug. If you confirmed or suspect you have grape leafroll virus in your vineyard and mealybugs are present, an insecticide application at this time may help to reduce the spread of leafroll. Most of the insects tend to stay under the bark of the trunk so it's difficult to get contact with them. The best choice is a systemic product such as Movento at the high label rate of 585 mL/ha (if you haven't already used it twice). Admire is registered for leafhopper control as a foliar and soil application; however, it is only locally systemic if applied as a foliar so will not reach the mealybugs, which are under the bark on the trunk. If you use Admire for leafhopper control, and apply it as a soil drench at 12 mL/100 m in sufficient water to insure incorporation into the root-zone just before a rain or irrigation, it will also control mealybugs. The drench should be applied in a band below the vines. A well-cleaned herbicide sprayer with large droplet nozzles (larger than you'd typically use for herbicide applications) would accomplish this. Admire can be applied in this way only once a year.
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|Author:||Wendy McFadden-Smith - Tender fruit and Grape IPM Specialist/OMAFRA|
|Creation Date:||23 July 2014|
|Last Reviewed:||23 July 2014|