Silverado Farming Company- Powdery Mildew Spore Traps


Silverado Farming Company is a full-service vineyard management company farming vineyards for wineries and growers in Napa and Sonoma Counties


To prevent powdery mildew, fungicides are typically applied on a 7-21 day interval using a predictive model based on temperature alone.  In 2019 we deployed traps to measure presence and abundance of powdery mildew spores in individual vineyards.  When spores were not found or when relative number of spores were very low, we increased our treatment intervals or eliminated planned applications.  On average we reduced fungicide sprays by 25%.

PROJECT STARTING DATE15 March 2019 ENDING DATE10 September 2019


Reduction of fungicide and diesel fuel use


Coastal Viticultural Consultants deploys and collects the trap data and posts the results on a web-based interface.


  • Preventative fungicide applications for powdery mildes are the most common pesticide application in California vineyards.
  • Reducing the number of sprays per year saves money, reduces fungicide use and reduces greenhouse gas emission from diesel-powered tractors.


Powdery mildew, Erysiphe necator, is the most common fungal disease in grapevines in California.  Serious mildew infections can lead to a reduction in crop yield and off-flavors in wine.  All green tissues are susceptible to infection from budbreak to veraison.  Because powdery mildew spreads by wind-driven spores, even if a vineyard has no mildew spores they can blow in from neighboring vineyards. Because of this, prevention is the best method of control. In the north coast of California fungicides are routinely sprayed on 7 to 21 day intervals.  These intervals are determined by the effective period of the fungicide and by determining disease pressure using the Gubler-Thomas powdery mildew model.  Typically, we spray 7-10 times per season.  The model assumes that mildew spores are always present.  But what if they are not?  Do we still need to spray?   Research in 2016 by Dr. Walt Mahaffee at Oregon State University developed a method of trapping wind-driven powdery mildew spores in the vineyard.

What are spore traps?

Spore traps function by monitoring fungal ascospore release in the field using a solar-powered collection mechanism and molecular analysis for identification. Traps are checked periodically throughout the growing season, and results are compared against fungal lifecycle models and grapevine phenological stage to determine infection risk. If models indicate a high environmental risk and there are spores present, growers may choose to treat vineyards (if vines are at a susceptible phenological stage).

There are two principal methods of identification: a diagnostic method and a quantitative method.

Growers may choose the diagnostic LAMP (loop-mediated isothermal amplification) method because of its ease of use and general reliability. This presence/absence test can be done in-house without a specialized lab, and it does not require very expensive equipment or extensive training. Results can be assessed by the naked eye. This method allows a grower to establish a disease management start date based on the presence of ascospores, not by intervals on a calendar or grapevine phenology. From that initial date, growers can begin their spray program based on their traditional protocols and intervals.

Most commercial labs will use a Quantitative Polymerase Chain Reaction (PCR) method. Quantitative PCR-based methods reveal the presence and number of ascospores existing during the trapping period. Knowing the number of spores further refines and educates management decisions. A grower can again initiate their spray program based on spore presence, but they also may choose to extend or compress a spray interval depending on the number of spores observed. These benefits in timing are particularly important when using fungicides with limited mobility and persistence (as with organic programs).2

Early results from academic studies indicate that trap location is more important than trap density when using this inoculum monitoring to educate management decisions. Growers should locate traps in perennial mildew “hotspots” within their own blocks or on the boundary of a neighboring vineyard. This will provide growers with an early warning of infection, often indicating disease presence before the observation of visual symptoms.

Combining spore trap data with disease pressure modeling has allowed us to eliminate two sprays per year from our programs on average. This reduces costs, reduces the amount of fungicide in the environment, and reduces fossil fuel use, consequently reducing the release of greenhouse gasses.

Research in regions with high disease pressure indicates that spore trapping can save up to four sprays throughout the growing season based on interval adjustment. Outside of obvious monetary and environmental savings, reducing the number of applications also supports better spray chemistry rotations. A prolonged cycle of chemistries allows more time before potential resistance accumulates.

Spore traps have also already been successful in capturing and identifying commercially important diseases such as Botrytis, downy mildew, and grapevine trunk diseases. As this technology matures, growers may use spore-trapping information to educate pruning decisions and late-season disease control. Further, these tests can be used to isolate and identify resistant fungal mutants, and therefore create better efficiencies in disease management.

What we do

Reprodutor de vídeo


Traps are placed in a location of the vineyard that catches the prevailing breeze and sent to a lab on a weekly basis.   Using qualitative PCR testing we can determine the presence and number of mildew spore and adjust our treatment intervals or eliminate a scheduled spray completely.  We always make an initial clean-up application soon after budbreak and always make an application at bloom as that is the most susceptible period.  The other times of the season we look at spore numbers and mildew pressure from climatic factors.  If here are no spores present, then we greatly lengthen the interval or eliminate the spray altogether.   If spores are present but at low numbers, then we lengthen the spray interval. If spores are at high numbers, then we shorten the spray intervals.

We contract with a service to install, maintain, and report trap results.  Growers could choose to construct their own traps and send them to a lab for testing.


Traps were deployed in 9 vineyards in 2019.  Fungicides were applied at budbreak and bloom and veraison regardless of the presence or abundance of spores in the traps.   For the periods between those sprays the intervals were increased or eliminated based on trap data.  2019 was a particularly difficult mildew year due to spring rains and warm but not hot conditions during the growing season.   We were able to reduce our sprays from 8 per year to 6 per year without suffering serious mildew infections.  On these 9 vineyards we reduced our diesel fuel consumption by 462 gallons, reducing CO2 emissions by 5.08 tons, which is the equivalent of removing 1.10 typical US passenger cars from the road every year.


Depending on the season we can plan to spray less in the future.  We are still fine-tuning how many traps per vineyard are needed and where they should be placed.  We have found that sometimes the number of spores in a trap will increase dramatically even if we cannot find any mildew in our vineyard.  In those cases it has been a neighboring vineyard that has mildew.  Communication with neighbors is valuable in this process


  • Increase the number of vineyards with spore traps


There is high potential for replication in other Silverado Farming Company vineyards, and also in neighboring vineyards in our area. If we deploy traps in all Silverado Farming Company Vineyards we could potentially use 2,220 gallons less diesel fuel per year reducing CO2 emissions by 24.5 tons or the equivalent of 5.33 passenger cars per year

There are other vineyards in our area using these traps, I would like to put together a cooperative user group to share trap data and results.


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