Vineyard at sunset

Mar 29, 2021
Mitigating grapevine trunk diseases: Using a new approach of a fungicide applied via drip paired with cultural practices

{Sponsored} The challenge of the grapevine trunk disease (GTD) complex present a problem unlike any others faced by grape growers. Most diseases they see are visible to the naked eye before they get out of control, but the problem with GTD is that it takes years of damage to the vines before growers start to see any evidence of infection.

“Almost 80% of vineyards in California, Washington and Oregon have some type of a wood disease,” said Issa Qandah, a plant pathologist and technical service manager for the Northern valley and coastal California for FMC Corporation.

How is a grower supposed to prevent infection when many pathogens are involved and it’s nearly impossible to tell anything is wrong until it’s too late?

Foliar fungicide won’t cut it

The problem is that a foliar fungicide is not effective for management or prevention of GTD. The reason is that GTD uses the xylem — the highways throughout the vines — to travel and infect the whole vine. Foliar fungicides are unable to penetrate the woody vines and, as a result, are not effective at treating GTD.

“If you are using a foliar fungicide to manage the pathogens, it becomes harder and harder (to treat GTD) because none of the foliar fungicides can go systemically through the xylem or the phylum to manage or reduce severity,” Qandah said.

With a 2(ee) recommendation*, Rhyme® fungicide works alongside the cultural practice growers currently use to reduce the chance of GTD development in grapevines. The cultural practices are important, though, and paired with the preventative action of Rhyme fungicide, they can add years of life to a vineyard, even if it’s already doomed by a GTD infestation. The fungicide has been tested for the past two years by Dr. Akif Eskalen’s lab at University of California-Davis, where Eskalen serves as a plant pathologist and UC Cooperative Extension Specialist in trees, vines and small fruit pathology.

Healthy grapevinesMode of action

Rhyme fungicide is a xylem-mobile fungicide that can move from the roots to the entire vine. The fungicide should be applied via a drip in areas where irrigation is predominantly used for optimal mobility within the vine. Up to 80% of the fungicide can travel throughout the entire structure (vine, cordons, branches, leaves and sometimes the fruiting structure) within the first 72 hours after application. It then suppresses the pathogens, preventing them from growing into healthy tissues.

The trickiest part of GTD is that it isn’t just one pathogen. “More than 130 different fungal diseases are involved — some less aggressive; some very aggressive,” Eskalen said. Eskalen explains that the pathogens that cause GTD basically colonize on the vine’s roots and then travel throughout the grapevine, destroying it over a period of years.

Of course, all of this applies specifically to live xylem tissue. These applications must be preventative in nature. Once the xylem is dead, the section of the vine that is no longer healthy must be removed and discard. As always, it is important to lean on university Extension pathology labs for accurate diagnosis. “Knowing what I have in my vineyard means 70% of the problem is solved. Then I know how to manage it and who to talk to,” Qandah said.

During precipitation, GTD can often release airborne fungal spores, quickly spreading the aggressive pathogens throughout the whole vineyard and possible nearby woody structures such as almond or walnut trees.

Cultural practices help Rhyme fungicide work best

As a result, cultural practices are also an important part in preventing spread of GTD along with the mitigating properties of Rhyme fungicide. Here’s what Eskalen recommends:

  1. Time your pruning correctly. Avoid pruning just before or just after rain, as that is when spore levels are highest.
  2. Delay pruning when possible to later in the season. When the vine is more active in warmer weather, the callosing that protects pruning cuts from being points of entry for the pathogens occurs faster, protecting the vine sooner.
  3. Get non-diseased plant materials when propagating new vines.
  4. Use machine pruning with sharp blades. The more jagged a cut is, the more surface area for fungal spores to attach to.
  5. Continue using products that prevent infestation for a short amount of time on freshly cut surfaces of the vine.
  6. Apply Rhyme fungicide via drip only for best preventative results.

Ultimately, Eskalen’s study showed that Rhyme fungicide performed very well in comparison to the control. And the study proved that the best application for Rhyme fungicide was the drip-only option. “Rhyme has good control and suppression of the pathogens causing grapevine trunk disease,” Qandah said, of Eskalen’s results.
Grapevines being fed via drip irrigation

Applying Rhyme Fungicide

For the best preventative action, Qandah recommends growers apply Rhyme fungicide via drip three times throughout the year. One application should happen in the middle of the season, which helps keep pressure on the pathogens, plus during the spring wood flush and fall growth to anchor it.

To learn more about Rhyme fungicide, visit


*This Rhyme fungicide recommendation is made as permitted under FIFRA Section 2(ee) for the management of wood disease complex on grapes in California. This recommendation has not been submitted to or approved by the EPA. The 2(ee) expiration date is 12/05/2024

Always read and follow all label directions, precautions and restrictions for use. Some products may not be registered for sale or use in all states. FMC, the FMC logo and Rhyme are trademarks of FMC Corporation or an affiliate.

©2021 FMC Corporation. All rights reserved.

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