Wine grape vineyards are highly susceptible to powdery mildew and botrytis bunch rot — two fungal diseases that can ruin fruit and result in unsellable wine. One proven, non-chemical method for reducing these diseases is the removal of leaves around the grape clusters, known as cluster zone leaf removal.
From 2009 to 2019, Oregon State University Extension viticulturist Patty Skinkis led research trials across various Oregon vineyards to better understand the timing and intensity of leaf removal and how it affects disease control and fruit quality. The trials showed that cluster zone leaf removal — whether applied to one or both sides of the vine — prevented both powdery mildew and Botrytis cinerea in commercial vineyard settings.
OSU Extension supports both environmental stewardship and economic resilience in one of Oregon’s signature industries.
This cultural practice is especially important for organic and biodynamic growers, whose disease management options are limited to a smaller set of approved fungicides. Leaf removal provides an additional tool to support healthy grapes while reducing reliance on chemicals.
Despite these findings, some winemakers in Oregon have moved away from leaf removal in recent years, citing concerns about exposing fruit to sun during increasingly hot, dry growing seasons. Others believed that white wine grapes, such as Chardonnay, should be protected from direct sun exposure.
To address these concerns and provide updated science-based guidance, the OSU viticulture team organized an educational event at the 2024 Oregon Wine Symposium. The session featured a technical wine tasting using Chardonnay made from a demonstration trial at Lingua Franca, a commercial vineyard and winery in Oregon’s Eola-Amity Hills AVA.
The field trial included three treatments: no leaf removal (control), single-sided removal, and double-sided removal, all applied during early fruit development. Grapes were harvested and processed using commercial winemaking practices. Symposium attendees learned about the trial design, field observations, and wine quality outcomes.
Participants tasted the three wines blind and rated their sensory characteristics. Wines from the single-sided leaf removal were described as fruity and bright. The control wines were noted as more floral, round and grassy, while the double-sided leaf removal wines were described as tropical.
When asked if they would adopt new leaf removal practices in the upcoming season:
- 71% said they planned to use single-sided early leaf removal
- 15% planned to remove leaves from both sides
- Only 5% said they would not use leaf removal
The event helped address grower hesitation around leaf removal in white wine grapes and demonstrated that early-season leaf removal can improve disease management and enhance wine quality — even in organic vineyards focused on premium production.
By helping vineyard managers adopt low-cost, sustainable practices like leaf removal, OSU Extension supports both environmental stewardship and economic resilience in one of Oregon’s signature industries. This work is especially important as more vineyards shift toward organic and biodynamic methods, where non-chemical disease control strategies are critical.
