top of page


What is a clean plant?

A clean plant is a plant that has been tested and found free of targeted pathogens and maintained in G1 blocks.  The G1 plants are then propagated in recognized certification programs. 

Why should I use clean plant material? 

Clean plants are key to higher quality, higher yield and cost-effective, sustainable production.  Studies show there is a clear benefit of using clean stock and that graft-transmissible diseases are costly. Once a crop is infected with these types of pathogens there is no cure. Often the infected plants or whole planting must be reestablished. In all cases, the best control strategy is prevention by using planting material derived from clean, foundation planting stock. For more details see the Economics Studies.


What are the economic benefits to using clean plants? What are the dangers of not using clean plants?

In citrus, costs due to Huanglongbing (HLB or Citrus Greening) are enormous:

  • Florida: $9 billion from 2006-2016, causing a 40% reduction in citrus acreage, 57% decrease in citrus operations, 34% reduction in juice processors, loss of 8,000 jobs

  • California: $40 million/yr to eradicate and suppress HLB and its vector

  • USDA: $400 million for HLB suppression in 8 years

In grapes:

  • Leafroll disease causes losses from $25,000 to over $226,000 per hectare over a 25-year lifespan of a vineyard in California

  • Grapevine red blotch disease causes losses from $2,200/hectare in Washington to $69,500/hectare in California over a 25-year lifespan of a vineyard

  • Grapevine leafroll-associated virus-3 losses estimated at $90 million/year in California

  • Pierce’s disease causes losses estimated at $92 million/year  in California

In fruit trees:

  • Plum pox virus (PPV) eradication program in Pennsylvania cost $59 million from 1999-2009; PPV causes losses of 810 hectares of orchards and over 2,500 trees destroyed

  • Little cherry disease and X-disease in Pacific NW caused an estimated 12% reduction of cherry production in 2020 and losses of 400 hectares of sweet cherry and 300 hectares of stone fruit trees

In sweetpotatoes, yield was reduced as much as 40% using common stock when compared with clean stock.

In blackberries, blackberry yellow vein disease causes rapid decline in yield and affected fields become unproductive in 5-7 years versus the normal 20 years. 

In hops, hop stunt disease is a devastating disease that can reduce hop yield by 60% or more.

In roses, viruses can include unsightly foliage, decreased vigor, and smaller and/or fewer flowers, and a significant decrease in the production.


How do I get clean plant material?

Most foundation level plant material produced by NCPN centers and programs is sold to nurseries. This is because the quantity of foundation level plant material is very limited. Nurseries then increase it and sell to the end user. Nurseries should contact a clean plant center or program that works with the crop of interest directly to submit an order. There are some exceptions. Check the crop page for more information. 

Which crops are in the network?

Currently, seven specialty crops are covered by NCPN centers: berries, citrus, fruit trees, grapes, hops,  roses, and sweetpotatoes. All of these crops share a similarity - they are primarily vegetatively propagated (not planted from seeds). An advantage of vegetative propagation is that they will be true to type because there is no genetic mixing. A disadvantage of vegetative propagation is that some pathogens, primarily viruses, can be carried in the propagation material without any outward symptoms only to increase and cause disease when the plant starts growing. The best method of control is to prevent the introduction of the pathogen by using clean plants to establish the crop.  

What is the NCPN?

The National Clean Plant Network (NCPN) is a voluntary association of specialty crop networks that have joined to promote the use of pathogen-tested, healthy plant material for specialty crops in the United States. The Network operates under the auspices of three USDA agencies: the Animal and Plant Health Inspection Service, the Agricultural Research Service and the National Institute of Food and Agriculture which agree to cooperatively support research, quarantine and outreach activities.

Does NCPN certify plant material?

No, NCPN does not certify plant material. Certification programs are administered by states.  For more information, see specific crop pages.


How do you eliminate pathogens?

Several types of therapies are used to eliminate pathogens from a cultivar.  One of the most common is  microshoot tip therapy which may be combined with heat therapy.  Microshoot tip therapy is the process of culturing microshoot tips from an infected plant to generate a population of new plants using tissue culture techniques. It is one of the most reliable methods and has been used for decades on a wide range of ornamental and crop plants. For more details see virus elimination page.

What pathogens do you test plant material for?

The list of targeted pathogens differs for each crop and is determined by a committee of scientists involved in NCPN who are at the cutting edge of research in their crop. It is based on economic impact  and availability of detection methodology as well as other factors. The list is revised as needed.


How can I get my plants tested for pathogens?

NCPN does not provide testing services but some participating clean plant centers and programs will test your plants for a fee. Contact the clean plant center directly for more information.  

Who funds NCPN?

NCPN is funded by the United States Department of Agriculture Animal and Plant Health Inspection Service (USDA-APHIS).

Where is the NCPN located?

The NCPN has over 40 participating programs and centers in 20 states throughout the United States.

Why was the NCPN started?

NCPN was started in response to eroded federal funding to state agricultural experiment stations, which in turn reduced funding to clean plant centers. At the time, it was the position of these institutions that practical service work did not serve their teaching and research mission. In addition, as faculty who worked on clean plant programs retired and were replaced by scientists with other interests, there was a risk of losing the body of knowledge and experience in managing clean plant programs. 

The importance of clean plant programs may not always be apparent, especially if there is no major disease outbreak. This is a continuous challenge - clean plant programs tend not to be glamorous and can easily be taken for granted due to the simple fact that using clean planting material is a preventative measure to manage diseases, much like good sanitation or vaccination. In grapes, the importance of clean plants became glaringly apparent in the 1950s when fanleaf degeneration was a serious concern. It was found that it could be controlled by using clean propagation material, which led to the formation of Foundation Plant Services (FPS) at the University of California, Davis in 1958.

When did the NCPN begin?

The NCPN began in 2008 after several years of discussions between stakeholders, industry members, scientists and other interested parties in the grape and fruit tree industries. In 2010, berries, citrus and hops commodity groups joined the Network, and in 2015, sweetpotato and rose groups were added.

What is a clean plant?
Why clean plant material?
Economic benefits and dangers
How to get clean plant material
Crops in network
What is NCPN?
Does NCPN certify plants?
Eliminate pathogens
Pathogen testing
Can I get my plants tested?
Who funds NCPN?
Where is NCPN located?
Why was NCPN started?
When did NCPN begin?
bottom of page