Feb 13, 2014
Viruses threaten berry nursery stock

When strawberry growers throughout the United States had their 2012-13 crop severely impacted by viruses traced to nursery stock coming out of a confined area in Canada, efforts were ramped up to negate such outbreaks in the future.

Conducted under the auspices of the National Clean Plant Network (NCPN), state-level model regulatory standards for certification of strawberry nursery stock – as well as other small fruit – are taking shape.

“I am working on developing a draft state-level model regulatory standard for the certification of strawberry nursery stock,” said Nancy Osterbauer, plant health program manager with the Oregon Department of Agriculture.

“Currently, each state that produces certified strawberry nursery stock has their own specific regulations with their own specific requirements,” Osterbauer said. “Our goal is to examine all of those individual regulations and look for the commonalities between them. We will also consider requirements that, ideally, should be common between them. Those commonalities will be the basis for the draft regulatory standard.”

The establishment of a state-level model regulatory standard, according to Osterbauer, “will serve several purposes. The benefits of having such a standard include access to new markets, the ability to trade stock interstate more easily and improved yields from growing certified plants.”

She said the standard will provide states that want to develop new regulations with a template to follow when developing their rules.

“It will ease interstate movement of plants by establishing basic requirements for risk mitigation that both exporting and importing states have agreed upon. Finally, assuming USDA APHIS adopts it as a national standard, it will provide USDA APHIS with a document they can use to enforce international phytosanitary requirements for strawberry nursery stock.”

She anticipates the work “will help protect U.S. growers from incidents like the one with virus-infected plants coming out of Canada. That incident is a prime example of what this effort is designed to address.”

How soon will the standard be put in place?

“We are in the information gathering stage right now and are collating all existing state regulations for certified strawberry nursery stock,” she said. “We will then hold a workshop that will involve subject matter experts, researchers, strawberry growers and nurserymen and state and federal regulatory officials. The goal of the workshop will be to develop the draft of the regulatory standard with input from all potentially affected stakeholders.”


According to Chuck Johnson, Extension plant pathologist at Virginia Tech, within four to six weeks of planting in 2012 a number of strawberry producers in Virginia (and other growers in the southeastern and mid-Atlantic states) began noticing poor growth in their fields – sometimes in certain spots, sometimes in virtually the entire field.

Similar problems were observed in Florida, North Carolina and other Southern states.

Because of the widespread nature of the symptoms and an apparent association with bare-root plants, or tips, from the Great Village area of Nova Scotia, Canada, Barclay Poling, a horticultural professor at North Carolina State University, traveled to the area to visit with Canadian strawberry plant growers and Extension staff, according to Johnson.

While there, Barclay was told that virus symptoms had started showing up in the fields of some strawberry cultivars in Great Valley in October (about the same time Virginia started experiencing problems).

“The Canadians had not had this problem before, and brought Bob Martin, a USDA-ARS small fruit virologist located at Oregon State University, in to help determine the cause,” Johnson wrote. “He collected plant samples in early November to take back to Oregon for laboratory testing, and his results were received while Barclay was in Canada.

“Dr. Martin found strawberry mild yellow edge virus (SMYEV) and strawberry mottle virus (SMoV) in samples from several matted-row varieties,” Johnson wrote. “Barclay noted that he had never before seen strawberry viruses to be a problem. Barclay also noted that Chandler plants in Canada looked healthier than other varieties he saw, such as Camarosa and Winter Star.

“All infected plants were plug plants produced from tips grown by one nursery in the Great Valley area,” Johnson wrote.

As far as was determined, no 2012-13 plants produced from any other source tested positive for a strawberry virus.

“Although this is our first experience with virus problems on strawberry, SMYEV and SMoV are very common around the world and often occur together and with other viruses. In fact, it may be that they only cause significant problems to strawberry growers when they occur together,” he wrote.

Organized effort

Ioannis Tzanetakis, associate professor of plant virology at the University of Arkansas, spoke on the subject of virus identification and management at the SE Regional Fruit & Vegetable Conference in Savannah, Ga., in January. He said those involved in strawberry plant production in Nova Scotia aggressively worked to correct the virus situation.

“They are really doing about 5,000 percent of what they should be doing to clean their material because they need to clear their name,” Tzanetakis said.

He said the onus on the nursery, research and grower communities to pinpoint strategies to avoid viruses is at a new high following the Canada stock scare.

NCPN is expanding its efforts to clean up plant material in nursery stocks in five major areas: berries, grapes, fruit trees, citrus and hops.

“Different groups are working on making national certification for different crops,” Tzanetakis said. “It’s an effort to make sure these things go through the propagation pipeline and be delivered to growers as really clean material.”

Tzanetakis has been involved in the process for blueberry, blackberry and raspberry nursery stock.

“Blueberry is the one pretty much to the point of being lined up in different states to drive those guidelines,” he said. “We expect the same thing with strawberry to take another two years for the guidelines.”

Tzanetakis said the impetus for the organization of NCPN came from the grape and fruit tree industries, who in 2005 initiated a series of meetings to explore the formation of a national group devoted to focusing on foundation materials that are tested, treated and maintained as a healthy source of plant materials for growers in the United States.

In 2008, the grape and fruit tree networks were developed by stakeholders, industry members, scientists and other interested parties for those respective specialty crops. In 2010, berries, citrus and hops were added to NCPN. Each specialty crop network has its own board and charter. Committees are made up of industry, nurseries, state representatives, regulators, researchers and growers.

The headquarters of the Berries Clean Plant Network is at the USDA Horticultural Crops Research Unit in Corvallis, Ore., led by Bob Martin.

“Nurseries, other than with the fiasco last year, do a fairly good job,” Tzanetakis said. “But we have not looked at, in the last 10 years, what is circulating in the nurseries. The things we are afraid of are the things we don’t know about. We have the ability to test for pretty much everything known or unknown in every single plant.

“We communicate with a lot of large nurseries on the West Coast, and they’re actually thrilled to participate,” he said.

Tzanetakis expects a final report on the strawberry work to be ready within the next three years. The organization is seeking a “large grant” from USDA to help fund the effort. Support also has come from the North American Strawberry Growers Association.

“I would say with strawberry right now, if you know your enemy you can deal with it. The good part about the whole strawberry industry is if you tell them what to do they will do it,” he said. “The issue is when you have a nursery going rogue – pretty much as in the case of Nova Scotia.”

“Development of standard operating procedures with everybody on board so we don’t have the types of problems we’ve had in the past” is what Tzanetakis hopes to see from the project.

He said work to coordinate standards with blackberry nursery stock would take a little longer.

“Blackberry is really a black box, with so many problems, unlike strawberry,” he said. “Blackberry is fairly immature. You have lots of people propagating by themselves and plants that remain in the ground for many years. When you have a problem like we had in strawberries last year, it’s now all gone. With blackberry, those would be in the ground five to seven or 10 years.

“We can’t tackle everything at the same time,” Tzanetakis said. “We’re working on blueberry as we speak. In the next year we expect to see something for nurseries in Oregon, Washington, New Jersey and Michigan. They are supposed to start testing the guidelines we have developed for propagation. This is really the end product. When it comes to certification, blueberry is definitely ahead of the other crops. We hope next year to get raspberries into that spot and, hopefully, strawberry after that.”

Gary Pullano

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