Vineyardists in the Pacific Northwest have been relatively lucky regarding the number of grape diseases they have to worry about. But recent experiences indicate that Washington growers should also watch for diseases associated with vine decline, and crown gall could again be a problem in the state.
In the mid-1990s, young California vineyards began showing vine decline symptoms, said Dr. Doug Gubler, pathologist from the University of California. Healthy vines were found next to stressed vines. Researchers could generally detect one or two fungi in the affected vines. A black streaking was found on the woody tissue when vines were cut for internal observation. As the survey scope expanded, he said that wherever vine decline was observed, it was also noticed that the vines were predisposed to some type of stress.
“You might see this in Washington in the future,” he warned during a grape disease seminar held at the Washington State University Tri-Cities branch in mid-January. His talk highlighted esca and Petri disease (also called young esca or young vine decline), both of which are caused by a complex of fungal pathogens. Esca typically occurs in older grapevines, seven to ten years old, while Petri disease, named after the Sicilian Lionello Petri, occurs on young vines.
Esca has been around forever. Gubler noted that the Greeks and Romans described the disease, and researchers believe it is mentioned in the Bible as “leaf scorching and fruit shriveling.” The primary pathogen associated with esca is the Phaeoacremonium genus, and several species are involved. A closely related fungus Phaeomonilla chlamydospora is responsible for Petri disease.
The diseases can come into a vineyard from infected nursery stock and are commonly found in the soil. A sign of infected nursery stock is dark streaking of the vascular tissue or a small hole inside the vine that can be observed by cutting the trunk vertically. Both diseases are endophytes and reside systemically in the wood and water-conducting tissues.
Vine decline symptoms
Symptoms of both diseases are expressed when the vines are under stress, such as poor irrigation management, deficit irrigation, early fruiting on vines before three years, and “J” rooting (when roots orient upward or laterally, but not downward).
Esca symptoms include tiger-striped pattern on the leaves, small chlorotic leaves, reduced shoot growth and shoot tip dieback, superficial brown spotting or measles on berries, berry shrivel, and acrid-tasting fruit. Other symptoms are streaking of the woody cylinder and stunted growth. With Petri disease, vines look weak, and the woody tissue shows black dots (pycnidia) or streaks. Black goo can ooze from cut vessels.
Esca fruit symptoms can be very destructive in table grapes. Gubler has seen table grape vineyards showing berry spotting in nearly 45 percent of the grapes.
With esca, perithecia overwinter in old pruning wounds to release millions of spores that are splashed and carried by the wind into new pruning wounds, creating new infections. Spore release is closely correlated with rainfall; scientists found no spores released in the hot, dry summer months.
“The idea is to prevent ‘J’ rooting,” he said. “The biggest thing is if you use a slit for planting, make sure the slit is wide enough and that the roots are pushed down.” Some growers are trimming or pruning the grapevine roots before planting, he said, adding that potted vines have not been a problem.
If infected vines are found, the entire vineyard does not need to be replanted, only the vines showing symptoms, he said.
He told Washington growers “don’t despair” if they see symptoms in their vineyards. “By establishing the roots first in a new vineyard before you start fruiting the vines, you can completely escape these diseases. If you restrict the rooting system and the fungus is there, then you’re liable to see some damage from it.”
Nurseries have improved their efforts to clean up vines, dipping plant material in fungicides like thiram and lime sulfur, he said. Painting pruning wounds in the field with Rally and Topsin-M, a new registration as a tractor spray combination, can control most fungi that enter pruning wounds. A boron-based paint also has been shown to be effective. And a new material, derived from insulated tiles used in space shuttle aircraft, is under study as a paint product.
Crown gall, caused by the Agrobacterium vitis pathogen, could be a problem again for Washington grape growers in 2011, following grape damage from last November’s freeze. WSU virologist Dr. Ken Eastwell warned growers that the state is primed for more winter injury and crown gall damage.
“Following winter damage, if you have crown gall, it can make a bad situation much worse,” he said, explaining that the big impact from the disease is the gall that crushes the vascular tissue of the plant, girdling the plant and restricting the movement of water and nutrients.
“Essentially, it’s strangling the plant,” Eastwell said. A gall covering 50 percent of the trunk surface is believed to result in 40 percent yield loss.
The disease, usually distributed in new planting material, can exist as a latent infection and requires injury, such as winter damage, mechanical, or grafting, to take hold. The pathogen resides within the host (grapevine) and is generally invisible until there’s been an injury, he noted. Bacteria are short lived outside the host material, but they are very good swimmers and can migrate in a vineyard through water films. Agrobacterium contains a gene that induces root lesions, which can be an entry site for root pathogens. Once the disease is established, problems recur year after year, and even if a new cane is trained up, that doesn’t mean the vine is free of disease.
Once established in a vineyard, there is no chemical control for the disease. Products like Gallex, Galltrol, and NoGall, will cauterize wounds but don’t eliminate the bacteria.
Economic impacts result in the loss of production and time and expense involved with replanting and retraining replacement vines. According to a Pennsylvania State University study, replacing 200 vines within a vineyard cost $6,000 in plant material and management costs, and over six years, resulted in $4,000 in lost grape sales and $40,000 in lost wine sales.
Virgin soil that hasn’t been planted to grapes is generally clean of crown gall, Eastwell said, noting that most infections arise from the planting of infected material. Infections are favored by soils that are moist, alkaline, and poorly drained. Ripping caliche layers before planting and having a site with good cold air drainage to prevent vine damage are good management tools. When grapes follow grapes, growers should control nematode populations before replanting and remove as much old root material as possible. Preplant fumigation can eliminate the bacteria, but also creates a biological vacuum by reducing all good soil bacteria, which can create later problems if crown gall is introduced.
Growers should always use certified plant material to keep viruses out of their vineyards. Ask the nursery what diseases the program tests for. The Northwest Grape Foundation Service uses tissue culture to eliminate bacterium during the propagation process, thereby eliminating crown gall. However, state certification programs vary, and not all eliminate crown gall.