top of page

Grapevines and the Clean Plant Process

Grapevines and the Clean Plant Process

A clean grapevine is a plant that has been tested and found free of specific viruses and other organisms that are known to cause issues with plant health. These clean grapevines are generated and maintained by centers within the National Clean Plant Network (NCPN). NCPN Centers distribute cuttings (rootstocks) and budwood (scions) from clean grapevines to nurseries and growers for further propagation and the generation of plantings stocks for vineyard production. In many states, the certified planting stocks found at nurseries originate from an NCPN Center. Growers are the drivers of the production and distribution of clean plants, and the adoption of certified planting stocks.


Dormant grape cuttings on their way to get packaged for distribution to nurseries and growers.

Economic Benefits of Using Clean Plants

Grapevines have many viral, bacterial, and phytoplasma diseases that are easily spread through cuttings when propagated. Many of these diseases can be spread from rootstock to scion or vice versa (i.e., graft transmissible). The first line of defense against such diseases is to plant healthy grapevines. There are major economic benefits to using clean planting stocks that originate from grapevines that are cleaned and maintained at NCPN Centers. These are typically available to growers as certified stock within the nursery. When diseased planting stock is used instead of certified or tested plant material, it is estimated that the wine grape industry has the following impacts:

  • In the 25-year lifespan of a vineyard, leafroll disease can cause a loss of $61,750 (New York) to over $558,458 (northern California) per acre depending on disease prevalence, yield reduction, price penalty for suboptimal fruit quality and the grape growing region.

  • In the 25-year lifespan of California and Washington vineyards, red blotch disease can cause a loss of $5,434 per acre (Washington) to $171,738 per acre (northern California) in red blotch disease related price penalties.

  • In California, Pierce’s disease costs the state $92 million a year in losses and control programs.

  • In California, the potential value of the grapevine leafroll-associated virus 3 screening program is $90 million a year.

BKN vineyard-3310 (2).jpg

What is a certified grapevine?

NCPN centers do not produce enough clean plants in volume to supply nurseries and grape growers for establishing vineyards. Rather, materials from clean grapevines are sent to nurseries for propagation to volume to meet grower needs. These clean grapevines remain clean by way of certification, and the nursery ensures that they follow their state certification guidelines. Most state certification programs follow strict guidelines established by that state’s department of agriculture to require routine pest management and testing of grapevines for detrimental viruses and their parent material. Certification standards vary between states, so check the NCPN website for your state certification program to see the specific standards required. The NCPN, along with state certification processes for the acquisition, propagation, and maintenance of clean grapevine stocks, ensure that grape growers have access to the best planting stocks possible.

How are clean grapevines produced at NCPN Centers?

The clean plant process begins when new plant material, referred to as an introduction or candidate plant, is submitted to an NCPN Center. These can be foreign imports, domestic selections, or new varieties direct from grapevine breeding programs.


The introduced grapevine then undergoes a series of disease testing panels to ensure it is free of targeted pathogens (select viruses, bacteria, and phytoplasmas). Testing panels are continuously evaluated, improved, and updated to reflect the latest developments in diagnostics, and any new pathogen discoveries.


If an introduced grapevine tests positive for any targeted pathogen, it undergoes pathogen elimination therapy such as microshoot tip therapy. After therapy, disease testing is repeated over time.


Once grapevines are free of detectable target pathogens through this testing and therapy process, they qualify as Foundation Generation 1 (G1) grapevines. This Foundation G1 material is what is maintained at the NCPN centers, either in a screenhouse or in an outdoor vineyard. Foundation G1 grapevines are regularly visually inspected and continuously monitored and tested for target pathogens.

This flowchart represents a generalized journey of a grapevine selection through a clean plant center in NCPN. Specific details may vary based on regional needs.  

From Foundation Clean Grapevines to State Certified Grapevines

Given that Foundation G1 grapevines are limited in supply and cannot accommodate the growing demand for state certified grapevines, there needs to be a process to produce more plants. When materials from a Foundation G1 plant are taken, those new grapevines are considered generation 2 (G2) grapevines. When materials are taken from G2 grapevines to further increase supply, those are called generation 3, or G3 grapevines. The same process continues to reach generation 4 or G4 grapevines.

Typically, nurseries purchase G1 materials to establish their own increase blocks, from which they can produce G2-G4 grapevines. Depending on the state, the grapevines that are propagated and undergo the certification process are typically planting stocks derived from G2-G4 plants. Therefore, grapevines sold as certified to growers originate first from G1 plants and then from G2-G4 plants.

Further Reading

Fuchs, M., et al. 2021. Economic studies reinforce efforts to safeguard specialty crops in the United States. Plant Disease 105:14-26.


Gergerich, Rose C., et al. 2015. Safeguarding fruit crops in the age of agricultural globalization. Plant Disease 99: 176-187.


Golino, D. A., et al. 2017. Regulatory aspects of grape viruses and virus diseases: certification, quarantine, and harmonization. Grapevine Viruses: Molecular Biology, Diagnostics and Management. Springer, Cham. 581-598.

bottom of page