Managing Powdery Mildew in the Vineyard

Managing Powdery Mildew in the Vineyard

The 2017 growing season in Washington was an unusual year for powdery mildew. Irregularly high soil moisture from abundant snow pack and rainfall combined with higher humidity from smoke and cloud cover to increase the threat of infection for many vineyards. In addition, many vineyards developed poor fungal management practices because of historically low risk in the area.

Grapevine powdery mildew can cause devastating and costly damage to your vineyard if not managed properly. With broad spectrum fungicides disrupting the ecological balance of your vineyard and targeted fungicides becoming less effective on resistant strains of powdery mildew, (Erysiphenecator), finding a solution to treat powdery mildew can be challenging.

Many vineyards tend to only worry about fungal infections in their fruit, however, foliar infections can inhibit photosynthesis and cause premature defoliation, and should be mitigated whenever possible. Even more devastating would be a complete failure, if left unmanaged. Early damage to vine foliage can result in poor fruit development, inconsistent flavors, and aromas.  

While fungal hyphae and chasmothecia can overwinter in dormant buds and in the vine bark, powdery mildew infections will not occur until after bud break when the temperature is well above 50°F It is also important to understand how weather patterns will affect your risk of infection, with mild temperatures and high humidity being the ideal conditions for powdery mildew growth. By assessing winter and early spring soil moisture, vineyards can get a sense for how their vines will develop, with available water and warmer temperatures resulting in more rapid growth.

The critical window for winegrape fruit infection is from intermediate pre-bloom to four weeks after fruit set. During this period vineyards are advised to review the best management practices laid out in the WSU Viticulture and Enology Extension News.

  1. Schedule your first seasonal spray before vine development gets to an unmanageable stage.
  2. Shorten spray intervals if vines develop rapidly to ensure all foliage is protected.
  3. Use vine training, shoot thinning and leaf removal to increase airflow, sunlight exposure and even foliar spray coverage.
  4. Monitor and manage vine health with Pollen Systems aerial overviews and monitoring systems. Then repeat step 3 as appropriate.

With the 2019 growing season underway, monitoring for fungal infections and validating the effectiveness of fungicide treatments will be critical to protect your vineyard. Using Pollen Systems’ NDVI and NDRE maps, you can validate the effects of foliar fungicide applications by monitoring the weekly health and vigor of vines in different application zones. Our newly developed ground based imaging technology can also assist in detecting powdery mildew, enabling you to target specific zones and reduce fungicide applications.

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