Grapevine specialists say nursery vines may not be disease free

A group of grapevine specialists warned on November 1 that growers planning new vineyards or replanting old blocks should not assume that vines bought from a nursery are free of damaging diseases, and said buyers should demand recent test results and clear traceability back to carefully screened mother plants.

The warning appeared in WineBusiness Monthly in an article written by 23 contributors tied to the grape sector and the National Clean Plant Network’s grape program. The authors said clean planting stock is available in the United States, but growers need to ask detailed questions before ordering because many nurseries handle both tested and untested material.

Their main message was direct: a vine sold by a nursery is not automatically a clean vine. According to the authors, many growers still assume nursery stock has already been checked for major pathogens. They said that assumption can be costly if infected material is planted and remains in the ground for years.

The article defines clean planting stock as a scion or rootstock propagated from “clean foundation vines” that have been extensively tested and found free of economically important viruses and other pathogens. The list includes grapevine fanleaf virus, leafroll viruses, red blotch, Pierce’s disease and phytoplasmas. The authors also noted an important limit to the system: in the United States, clean foundation vines are not tested for Allorhizobium vitis, the bacterium linked to crown gall, or for wood-colonizing fungi associated with trunk diseases.

The specialists said clean foundation vines are usually produced and maintained by Clean Plant Centers affiliated with the National Clean Plant Network, a USDA Animal and Plant Health Inspection Service program. Those centers are located in California, Florida, Missouri, New York, North Carolina and Washington. Their work, the article said, depends on industry money, federal funding and institutional support.

Producing a clean foundation vine is slow and expensive. The authors said the process usually takes about five to 10 years and can cost about $10,000 to $15,000 per foundation vine. It begins with intensive testing, including high-throughput sequencing, bioinformatics and polymerase chain reaction-based assays. Once a vine is accepted into a clean foundation collection, it continues to be monitored every year to make sure it has not been infected by pathogens spread by insect vectors or other pests, including mealybugs, soft scales, leafhoppers, treehoppers, planthoppers, psyllids, spittlebugs and dagger nematodes.

Because clean plant centers keep only a small number of each clean foundation accession, nurseries receive propagation material and multiply it in later generations. The article said those first clean foundation plants are known as G1 vines. Material then moves to nursery increase blocks, where it becomes G2, G3 or sometimes G4 material before being used to produce grafted or own-rooted vines for sale. That scale-up is essential for commercial supply, but the authors said it also creates more opportunity for reinfection as material gets further removed from the original G1 source.

Testing and oversight at that stage are not uniform across the country. The article said later-generation vines are usually monitored at the vineyard scale rather than vine by vine, and that state certification programs differ widely in both testing frequency and protocols. The National Clean Plant Network is not responsible for that nursery-level certification work.

That gap is why the authors urged growers to treat plant purchases more like a documented health check than a routine order. They recommended that growers place orders at least one year before planting and ask exactly which pathogen tests were performed on the mother vines used for propagation. They also said growers should request recent negative results from a reliable laboratory and ask who performed the tests, when they were run and what methods were used.

The article advised growers to go further when possible. One recommendation was to visit the nursery’s mother blocks in the fall, when symptoms of some vine diseases are easier to see. Another was to ask whether the scion and rootstock material for the order comes from G2, G3 or G4 vines that have tested negative for unwanted pathogens and pests over at least two consecutive years. If confidence remains low, the authors said growers should consider collecting samples themselves from the mother vines that will be used for their order and sending them to a laboratory whose accuracy has been independently verified.

The warning comes at a difficult time for the U.S. grape industry. The authors said growers across the country are dealing with unusual weather patterns, shifting market demand, new national policies and unstable international trade conditions. In California, they said, thousands of vineyard acres have been removed as part of a painful restructuring process. Even so, they argued that future plantings should be planned carefully and built on healthy stock so that the next investment cycle does not begin with preventable disease problems.

For wineries and the broader drinks business, the issue reaches beyond farm management. Infected planting material can shorten vineyard life, weaken vine growth and cut yields, which can raise replacement costs and reduce long-term supply stability. The authors said economically important viruses can also lower fruit quality and alter wine sensory attributes, making the health status of planting stock a matter with potential consequences for grape quality, production costs and finished wine.

They put a number on that risk, estimating that viruses of economic concern can cost as much as $4,000 per acre each year through lower vigor, reduced production, lower fruit quality and failed or underperforming plantings. The article included a comparison between vineyard blocks established with cleaner and less clean stock, showing visible leaf reddening tied to leafroll disease in the weaker block.

At the same time, the authors said buying clean vines is not a complete answer on its own. Clean stock must still be protected after planting through sound viticulture, regular scouting and control of disease vectors. In other words, a clean start lowers risk, but it does not remove the need for ongoing management in the field.

The article’s contributors included university scientists, extension educators, nursery executives, state agriculture officials, a winery representative and other industry specialists. Many are members or affiliates of the National Clean Plant Network’s grape board. Their shared conclusion was that clean planting stock is available in the market, but growers need to actively select it rather than assume they are getting it.

That means asking more questions before money changes hands. It also means treating traceability and test records as part of the product itself. For growers preparing the next vineyard block, the authors said, that level of scrutiny can make the difference between a profitable planting and years of problems rooted in the first vines that went into the ground.