—by the Washington State Department of Agriculture, the Washington Wine Industry Foundation and the Clean Plant Center Northwest 

The Washington State Department of Agriculture Plant Services Program administers eight planting-stock certification programs for various crops, including seed potatoes, grapevines, fruit trees, hops, mint, garlic, cane berries and strawberries. The program also regularly surveys pests and diseases in Washington nurseries. 

Planting certified material helps prevent the introduction and/or spread of many unwanted diseases. Unlike insects and many fungal diseases, the viruses, viroids, phytoplasmas and bacteria addressed by certification programs cannot be controlled by chemical sprays after plants are infected. Once disease is established, it is difficult and costly to eradicate. Planting “certified” plants is the best insurance for a healthy and profitable farm.

Four years ago, the Washington State Department of Agriculture’s nursery research funding program awarded the Washington Wine Industry Foundation and the Clean Plant Center Northwest financial support for a project called “Building Awareness of State Certification Programs for Fruit Tree, Grapevine and Hop Planting Stock.” The funds from the multiyear grant were used to promote awareness and increase nursery and grower adoption of certified planting stock and to address industry confusion by clarifying between planting stock that is clean, registered and certified. The target audience included grape, fruit tree and hop nurseries as well as the tree fruit, grape and hop growers themselves. This article and the accompanying Q&A were written as part of that effort to educate and clarify terminology.

Fruit trees

Since the 1950s, the WSDA’s fruit tree registration and certification program has served Washington’s $2.4 billion apple, pear and cherry fruit production systems by ensuring healthy, virus-tested planting stock for fruit tree nurseries.

WSDA virologists monitor trees in several different ways, including visual inspection, greenhouse indexing, field indexing and molecular testing so that participating nurseries can produce certified Generation 4 (G4) trees for wholesale and retail sale. The certification program manages over 90,000 registered G2/G3 pome and stone fruit mother trees, which means millions of certified trees and rootstocks can be produced annually by 14 nurseries enrolled in the voluntary WSDA program.

The WSDA program is co-located with the Clean Plant Center Northwest in Prosser, Washington, on the campus of WSU’s Irrigated Agriculture Research and Extension Center. The center, part of the National Clean Plant Network, acts as a source of fully tested G1 foundation material entering the certification program. WSDA maintains a state-of-the-art, 45,000 square foot virus-indexing greenhouse at Prosser, as well as a molecular lab, nematology lab and field plantings of seed source trees.

Nurseries that participate in the program rely on budwood and rootstocks that have been tested for known viruses. They then isolate the G2/G3 registered mother block plantings from noncertified stock and take steps to exclude virus vectors and control broadleaf weeds, so the risk of infection with local, regionally occurring viruses is greatly reduced. Planting WSDA-certified trees can mean growers have longer-lived, higher-yielding orchards. Certified tree production also gives Washington nurseries export access to foreign markets for their nursery stock, which must meet rigorous international requirements for pest control. 

For more information on enrolling in the WSDA fruit tree certification program, call Segun Akinbade at 509-786-9275.

Grapevines

The availability of virus-tested grape planting stock is important to the success of vineyards and the wine industry in Washington state — the economic impact of which is valued at $9.5 billion, according to the Washington State Wine Commission. WSDA’s Grape Planting Stock Certification Program was established in 2002 and now inspects and tests over 200,000 registered G2/G3 mother vines at participating nurseries each year. All mother vines in the program must be sourced from clean, virus-tested G1 foundation material maintained at a nursery enrolled in the National Clean Plant Network. The program requires isolation distances from noncertified stock at nurseries, vector control and annual molecular testing of registered G2/G3 mother vines for grapevine leafroll-
associated virus 3 and grapevine red blotch virus, plus a subset of samples are tested for Xylella fastidiosa, the pathogen that causes Pierce’s disease. Each year, millions of certified vines are produced by four nurseries in the program and sold to vineyards and retail nurseries domestically and internationally as own-rooted vines or grafted vines (if the source rootstock is from a certified source). 

The Clean Plant Center Northwest serves as a source for virus-tested G1 foundation grapevine material. These G1 vines are maintained in insect-proof screenhouses and tested regularly to ensure they are clean and virus-free. Cuttings from G1 vines are used to establish registered G2/G3 mother vines at nurseries enrolled in the certification program. 

The WSDA certification program collaborates with WSU to conduct annual molecular testing of the registered G2/G3 mother vines for regional viruses of concern to the industry. 

In addition, grape growers in Washington are protected by a state quarantine (WAC 16-483) that requires all grapevines originating out of state to be produced under a certification program and found free of certain pests and diseases. Currently only Oregon and California have certification programs that meet Washington’s quarantine standards. 

For more information on enrolling in the WSDA grapevine certification program, call Benita Matheson at 360-410-1260. •

Q&A: The language of clean plants

Q. What is a clean plant?

A. A clean plant, also known as Generation 1 (G1) foundation material, has been tested and found to be free from all viruses, viroids and systemically infecting pathogens not specifically exempted by a clean plant center and all states with national certification programs. G1 foundation plants are maintained at a nursery that is part of the National Clean Plant Network, and they are planted under controlled conditions to prevent infection or reinfection.

Q. Wait, G1? How many G-levels or generations are there? 

A. There are four levels. Generation 2 (G2) plants are propagated from G1 plants to establish registered mother trees or vines at a nursery participating in a certification program. 

Generation 3 (G3) plants are propagated from G2 plants to further expand a registered mother block. 

Generation 4 (G4) plants are the final level in a certification program. Finished G4 trees or vines are also called “certified” and are sold directly to consumers, growers and retailers. 

Q. OK, so what is a certified plant?

A. A certified plant is a G4 plant that has been grown at a nursery enrolled in a state certification program and that can trace its origins to a foundation source at a nursery in the National Clean Plant Network or other approved source. The participating nursery must follow the rules of the certification program for that crop. 

Q. How does a plant become certified?

A. The label “certified” is the result of a healthy plant being propagated using procedures to minimize infection and disease spread, and this process is legally defined by each state’s Department of Agriculture. In this process, a registered mother block is planted at a nursery with plants obtained from a G1 foundation source. State regulations govern the details of how registered mother block planting is done and specifies acceptable plant sources, block isolation distances and other operation parameters. Plants from the registered mother block are propagated to produce certified plants. If a plant is grafted onto rootstock, both the scion and the rootstock must meet these standards to qualify as certified.

Q. How do I know if plants are certified?

A. Nurseries in certification programs use tags approved by their state’s Department of Agriculture for labeling certified plants. Certification status can also be verified on nursery invoices. Currently, Washington only recognizes certification programs in Washington, Oregon and California for grapevines. 

Q. What is a quarantine?

A. A quarantine is a restriction on transporting plant materials across specific boundaries. Quarantines are necessary to prevent the introduction and spread of unwanted pests and diseases from one area to another. Federal quarantines regulate plant imports from other countries. Washington state has quarantines for hops, grapevines, garlic, mint and seed potatoes that originate from other states and U.S. territories. These quarantines help to protect agricultural industries in Washington. Washington’s grapevine quarantine can be found under WAC 16-483. 

Q. Where can I get clean plants and more information? 

A. Only purchase plants from reputable nurseries and purchase “certified” whenever possible, but also verify that they are certified.

More information about the Clean Plant Center Northwest, which provides propagative materials from foundation plants, can be found online at: cpcnorthwest.com/s.

For more information on WSDA planting stock certification, go to: bit.ly/wsda-plant-certification or call 360-902-1874. •