SATI Beyond The Bunch 4th Quarter 2025

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Scouting for ants in grape vines is an essential part of mealy bug management.

Monitoring There are three ways to monitor mealy bug infestations, and all of these should be used when deciding on appropriate management strategies. Vineyard history Classify vineyards according to the observation of bunch infestations in the vineyard and the pack house. A vineyard with very few or no infested bun ches shouldn’t need dormant spray applications or aggressive crawler control. Substantial bunch infes tations indicate a greater need for chemical control. Mealy bugs are frequently unevenly distributed within vineyards. If bunch infestations are at economically meaningful levels, it’s advisable to identify and address mealy bug hotspots in the vineyard rather than jumping to blanket spray applications. Scouting In-depth scouting should be done once during winter to find and eliminate colonies of adult females. Start summer scouting from bud break and continue until harvest. Every block must be scouted weekly, so farms need enough trained scouts to avoid missing infestations. Check for adults and crawlers. Crawlers are the easiest stage to control because they’re exposed: they aren’t hiding in cracks, and they haven’t yet developed protective waxy coatings. It’s also essential to target crawlers before they reach bunches.

Mark infested vines during the season so they can be used to assess the efficacy of control measures and to detect crawler activity early in the following season. Pheromone traps Winged mealy bug males can be caught with pheromone-baited traps hung in the vine canopy. Traps attract males powerfully, but males are not strong fliers. Therefore, the best place for traps is near suspected hotspots. Traps at the vineyard edges may attract males from outside the vineyard. Deploy traps in September and check them weekly. The lures should be replaced according to the manufacturer’s recommendations. Trapping should continue at least until harvest. In problem blocks, continue checking traps monthly after harvest. Male mealy bugs are very small (± 1.0–1.5 mm long) and must be identified using a stereomicroscope. Scout for crawlers once males appear in traps. There are no thresholds for mealy bug trap catches, but 65 males per trap in two weeks indicates that scouting for crawlers should intensify. Peak crawler movement tends to shift a week earlier or later every season, but mass crawler migrations usually occur 1–2 weeks after males are trapped. However, the relationship between male numbers and crawler movement is site-dependent, so trap catches and crawler activity must be correlated based on historical data.

Scouting protocol 1. Divide the block into 20 plots of equal size, each containing five vines. Plots should be evenly spaced but include suspected hotspots. 2. Check for adult females under the bark. Check for all life stages on stems, leaves, and bunches. Infestations tend to start on stems, move to leaves, and end up on bunches. 3. Examine all new growth on each vine using a hand lens. Adult females are easily spotted with the naked eye, but crawlers can be less than 0.5 mm long. 4. Chemical control to prevent economic damage is unnecessary if fewer than 2% of vines have infested

stems. A mass release of natural enemies should be considered instead. 5. Check for ant activity. Control ants if more than 20% of vines are infested.

BEYOND THE BUNCH • 7 • QUARTER 4 • 2025