Home Video Growing Forward: Session 1 Addresses Powdery Mildew and Soil Moisture Monitoring

Growing Forward: Session 1 Addresses Powdery Mildew and Soil Moisture Monitoring


On March 31, Wine Industry Network welcomed attendees to its first Growing Forward seminar of 2022. Unlike last year’s debut of the topic, this year the online event will be split into three distinct parts, each airing at different points throughout the year to address growers’ concerns in seasonally appropriate sessions. Parts 2 and 3 will air in July and November, respectively.

This first session, titled “New Learnings & Best Practices on Grape Powdery Mildew and Soil Moisture Monitoring,” was sponsored by Turrentine Brokerage and moderated by Bryan Rahn of Coastal Viticultural Consultants (CVC). 

Bryan Rahn, Coastal Viticulture Consultants
Bryan Rahn, Coastal Viticulture Consultants

Rahn jumped right in, stressing the importance of early detection when dealing with powdery mildew and explaining that, contrary to previous beliefs, powdery mildew mold spores are not always present in vineyards. The discovery was made via spore traps, which can be installed throughout a vineyard to detect the presence of spores. The traps can detect even small amounts of spores — in the single digits —to help target mitigation efforts early.

The goal, he says, is to use early treatments (oils, sulfur, etc.), with lower risks of resistance development, rather than more harmful fungicides, and to “stretch” the intervals between treatment for as long as possible. Weekly readings can guide spray patterns and frequency. 

Changing Data, Changing Minds

The CVC Ag app, which Rahn developed with his son, Dylan, monitors the spore traps daily. It also surveys for spores by area — not vineyard by vineyard — so neighboring growers can share data, establish checks and balances, and work together to quickly mitigate a detected outbreak.

Dylan Rahn, Coastal Viticulture Consultants
Dylan Rahn, Coastal Viticulture Consultants

The Rahns opened the discussion to Matt Frank, senior director of vineyard operations for Trinchero Family Estates, and Allison Bettis, viticulturist at Silver Oak and Twomey. Frank has been using the CVC spore traps and data for four years, initially only to observe the data, as he found it difficult to trust the new means of detection, not to mention follow the recommendations to forego regular spraying in favor of “stretching” between treatments. By year three, however, he reports a detectable ROI; TWE is now using spore detectors in all of its vineyards.

Bettis, too, was nervous about changing set practices. But she soon found herself stretching intervals and eliminating more expensive sprays (which, in turn, eliminated tractor passes, leading to healthier soils). Her company is now using traps in all of its Napa and Sonoma county vineyards. She’s already better able to understand emerging patterns and be prepared with minimal interventions first.

Spend Water Like Money

The second piece of the day’s presentation focused on soil moisture and optimizing vineyard irrigation, especially in times of drought and water insecurity. 

Rahn listed seven practices for water conservation in the vineyard, including the mantra “Spend Water Like Money.” More practical advice included evaluating equipment to ensure efficiency, irrigating by soil type, knowing your rooting depth, planting drought-tolerant rootstock, understanding soil-to-water-to-plant relationships, and using vapor pressure deficit (VPD) techniques for irrigation decisions. Of these, he says, miswatering by soil types is the most common mistake.

Use a soil survey to understand your water needs, he advises. And keep your grape varieties in mind as well. Know which ones need more or less water to develop properly. Monitor all phases of growth — plant, bud and canopy, flower, fruit, and ripening — as the effects of water stress can include shatter at bloom, weak growth and defoliation, lower yields and reduced quality, reduced bud fruitfulness, and smaller spurs or canes at pruning. 

One way to protect your vines is to monitor leaf/canopy temperature in real time. Using water to cool things down when needed can protect development of flavinoids and tannins in the fruit. Frank and Bettis agreed that the best outcome is year-over-year consistency. To achieve that, monitor temperature daily and water levels as often as possible. And those with limited water supply should anticipate and prioritize managing heat spikes. 

A grower himself, Rahn says vineyard longevity is directly tied to soil health. The most important jobs, he says, are to grow your canopy and to set the crop. Making data-driven decisions is the best way to get that done.

Watch the replay here.


Alexandra Russell

Alexandra Russel headshotAlexandra Russell is Managing Editor at Wine Industry Advisor. She can be reached at [email protected]

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