Diseases Fresh Grapes Grapes Insects Pest Management Wine Grapes

Sooty mould — a sure sign of mealybugs (and sometimes scales)

W. McFadden-Smith (OMAFRA), S. Poojari and J.P. Parent (AAFC)

A few weeks ago, it was easy to find mealybugs and scales on foliage and fruit in vineyards that had not been sprayed with Movento.  Mealybugs and scales secrete a sugary substance that not only attracts ants, but also acts as a food source for superficial sooty mould fungi.  The latter are not an issue for wine grapes but can make table grapes unmarketable.  However, the presence of sooty mould is a good indicator of the presence of the vectors of Grapevine Leafroll-associated Viruses (GLR-aVs).

Click photo for full-size image.

Grapes with sooty mould growth as a result of mealybug infestation (Aug 28)

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Mealybug in cluster with sooty mould (Aug 28)

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Mealybug egg clusters under trunk bark (Sept 5)

Egg clusters are now the most prevalent growth stage of mealybugs.  This means that even if Movento is applied now, the insects are no long feeding so it won’t kill anything.  Since there is no information suggesting that a post-harvest application of Movento would still be active until the spring when feeding would resume, at this point, the sooty mould should just act as a red flag that mealybugs are present and should be controlled next year.

The timing for Movento sprays to target first instars in the growing season is shortly after bloom (or prebloom if you’re targeting Phylloxera too).  If Movento is applied much before that, it will not move down into the vascular tissue in the trunk where the mealybugs are feeding.  A second application 30 days later will provide activity for the rest of the season.  Movento is labeled for suppression of scales.  However, scales are not as efficient at transmitting virus so suppression may be enough.

Click the link for a pdf of this article: Sooty mould and mealybugs

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