Conquering Vineyard Diseases From Root to Fruit 

By: Cheryl Gray

Vineyards are constantly on alert for bacteria and fungi, both of which can cause debilitating diseases––persistent threats to an otherwise healthy grape crop if not put in check right away.

  The names of these culprits sound ominous. They include black rot, grapevine trunk diseases, powdery mildew, Phomopsis, Phylloxera and Botrytis bunch rot. They are as intimidating as they sound, causing damage to plant roots, trunks, branches, leaves and ultimately, grapes.

  Madeleine Rowan-Davis, a senior viticulturist for Atlas Vineyard Management of Napa, California, describes the challenges of the vineyards in her region and throughout the country.

  “I don’t believe there is a grape grower in the U.S. that does not have a fungicide plan in place for prevention of powdery mildew. After powdery mildew, the next biggest culprit we deal with in wine grapes is Botrytis or grey mold. Botrytis grows under damp conditions and can damage the flowers during bloom, reducing yields; and also [damage] the nearly ripe fruit following heavy dew events or pre-harvest rain. It is absolutely crushing to spray all season preventing powdery mildew and then lose fruit right before harvest to bunch rot caused by Botrytis.”

  Almost anything that is not in a grower’s control, things like insects, weather and other environmental factors, can introduce bacteria and fungi to vineyard plants and, in turn, thwart a grape crop before it even starts. 

  On the flip side, experts say that some growers can unintentionally promote the growth of bacteria and fungi by doing what most consider routine tasks. For example, some industry experts caution that repeatedly using the same chemical treatment can lead to bacteria and fungi resistance, eventually rendering that treatment ineffective. Another problem is deploying flood irrigation, which promotes the growth of fungus-like powdery mildew and other culprits that feed on humidity. Still another practice is fall clean-up. After harvest, some growers use fertilizer and water as a clean-up spray. But just because there are no grapes around doesn’t mean that bacteria and fungi are absent. If growers aren’t careful, the practice of fall clean-up can create the perfect breeding ground for fungi and other pathogens. 

  Among the best at helping grape growers protect their fruit is Suterra, a global leader in the industry. In business for more than 30 years, the company produces hundreds of products used in growing regions across the globe, including more than 400,000 acres in California.

  Suterra’s state-of-the-art facility in Bend, Oregon, combines all aspects of its business under one roof. Research and development, product engineering, manufacturing and the company’s signature, large-scale pheromone synthesis work seamlessly to create innovative weapons for vineyards to use in guarding against damaging invasions of disease and fungi.

  Emily J. Symmes is Senior Manager of Technical Field Services for Suterra. She gives an overview of the major disease and fungi threats to vineyards.

“Some examples of common fungal diseases that are often considered perennial threats, meaning that they may appear each year and require some degree of management, are powdery mildew and Botrytis. While significant negative impacts can occur due to these types of infections, the spread of virus diseases in a vineyard is often more concerning.”

  Suterra partners with trial collaborators each growing season to innovate and continuously improve its products based upon what growers need. Its CheckMate VMB-F sprayable pheromone is now on the California Certified Organic Farmers list of allowable products for use by organic growers. The company also works with growers to tailor and improve dispenser design, longevity and ease of deployment. Suterra is currently working on a new type of dispenser for the vine market. According to the company, testing this latest innovation has produced favorable results from growers. 

  Symmes shares best practices on how vineyards can lessen the impact of disease and fungi on their plants and fruit. In many cases, she says, it’s virtually impossible to avoid them all. Rather, she cautions, mitigation is the operative word.

  “With the more perennial fungal pathogens, a number of factors can contribute to the severity of the problem. These are largely driven by weather conditions and microclimate factors within the vineyard canopy structure. Because of this, there are often cultural methods that can be implemented to discourage fungal growth. In addition, there are fungicides that, when applied properly and at the appropriate times, are effective at preventing severe damage. When it comes to viruses, unfortunately, there are no curative treatments. The goal then becomes preventing virus introduction and minimizing spread.”

  According to a study funded by the USDA and conducted by the University of Massachusetts Extension Plant Diagnostic Lab, one of the worst diseases for vineyards is the Grapevine Leafroll Associated Virus complex. While this virus has variations, all of them cause the dreaded symptoms of grapevine leafroll disease. Experts say its impact hits vineyards from California to New York state.

  Dr. Symmes describes Suterra’s products and how they function to protect vineyards from bacteria and fungi, some of which are carried from vine to vine by insects.

  Suterra manufacturers CheckMate VMB-XL, a membrane dispenser, and CheckMate VMB-F, a sprayable microencapsulated formulation. These products target vine mealybug, a highly efficient Grapevine Leafroll-associated Viruses vector. The active ingredient in both products is synthetic replicas of the vine mealybug’s sexual reproduction pheromone.

  By hanging VMB-XL dispensers or spraying VMB-F microcapsules, the natural ability of males to find females to mate is inhibited. These solutions limit reproductive capacity, lower populations, reduce direct crop damage caused by the pest and minimize the potential spread of GLRaVs.

Vine mealybug also produces large amounts of honeydew as a byproduct of their feeding. Sooty mold, another fungal pathogen, uses the honeydew as a substrate for development and can cause grape bunches to be unmarketable. By controlling VMB, the impacts of sooty mold can be avoided.

  ORCAL is another Oregon-based company specializing in industry-leading products that help vineyards develop best practices for protecting their grapes. The company was founded in 1997 and is located in Willamette Valley, a major agricultural region and home to a number of world-renowned vineyards.

  ORCAL promotes crop protection and sustainable farming through aggressive research and development, continuous education and innovative technology. It promotes its products as industry-leading and prides itself on building and maintaining integrity with its business clients and associates. Its services range from custom formulations to product packaging.

  One of the company’s game-changing products is Lime Sulfur Ultra, which is described as a three-in-one product, making it a viable weapon in the fight against vineyard diseases caused by bacteria and fungi. Thomas Putzel is Territory Manager for ORCAL. He describes how his company reinvented the use of an old-school method, transforming it for today’s needs.

  “When most people think of lime sulfur, they think of the high rates and that they are only safe to use during the dormant period. That might have been true 100 years ago with the older technology. This is not the case with Lime Sulfur Ultra. The reduced rates have many benefits—first, the fewer chemicals of any kind we are using, the better, including organic chemicals. Lime Sulfur Ultra is every bit as effective at controlling all the same pests as traditional lime sulfurs with a fraction of the rate. This reduces the carbon footprint and resources needed to control a wide host of pests plaguing growers today. Also, it isn’t just a fungicide; it is a miticide and insecticide as well. When we are able to do more with less, that not only has an impact on our environment but also a grower’s budget and bottom line.”

  For growers who want management services to mitigate the threat of disease in their vineyards, there are companies like Atlas Vineyard Management. As the firm’s senior viticulturist, Rowan-Davis says the responsibility to protect vineyards from disease is year-round, including guarding against the pests that can spread disease.

  “For each of our farming clients, we provide a pre-season customized chemical application plan and then support that plan in-season with our scouting service. This allows us to respond to seasonal shifts as well as new pests as they arrive. In some cases, our customers are very involved in these decisions, while in others, we simply act and do what is needed to produce high quality, clean fruit for harvest.”

  As there is no cure for many of the diseases caused by bacteria and fungi in vineyards, a plan of defense is key to fighting this ever-present danger. Clean planting, early treatment and strategic planning to thwart ingredient resistance are essential tools in minimizing the threat of vineyard disease.

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