Why should I be selective about the planting stock used to establish a new vineyard?

The choice of planting stock will have an enormous impact on the health and quality of the planting for the life of the vineyard. If virus-infected planting stock is used, no subsequent cultivation practices or treatments will improve the diseased condition, short of replacing the vines.

Grapevines carrying virus disease are a liability to the grower for many reasons. The adverse effects of virus disease range from delayed ripening and reduced sugar, color, and yield (as is the case with leafroll) to leaf malformation, shot berry fruit, and yields that may drop to zero (as is the case wish fanleaf). Fanleaf-infected vines can also serve as a source of infection if Xiphinema index dagger nematodes are present in the soil to transmit the virus to healthy vines. These nematodes can survive up to 10 years on roots left behind after a vineyard is removed and will infect healthy vines that are planted later in the same site. Virus disease should therefore be avoided for the betterment of current and future vineyards.

It is also important to choose planting stock that is true to variety. If the vines are found to be incorrectly identified, they may be unsuitable for the product for which they were planted. Costly procedures such as replanting or grafting over are the only way to correct this kind of mistake.

Can I determine whether my planting stock is disease-free and true-to-variety with a visual inspection?

Not always. It is difficult to determine the disease status or variety of a grapevine from a dormant cutting or dormant plant. Some diseases do show characteristic symptoms in growing vines, but these vary according to the host variety and the particular virus disease(s) involved. Consequently, it is not possible in all cases to reliably determine the health of grape planting stock by looking at vines.

About 30 years ago scientists responded to the problem of determining a vine's virus disease status by developing a technique called "indexing" to test for graft-transmissible virus disease(s) in grapevines. To index, chip buds from a candidate selection are grafted onto several specific grape varieties, called indicator varieties, that display distinct visual diagnostic symptoms when infected with particular virus diseases. If the candidate is virus-infected, the indicator plants will show symptoms in about 18 months. Some viruses can also be detected by smearing ground-up leaf tissue from the candidate onto a greenhouse-grown weed called Chenopodium quinoa. If the virus is present, the weed shows symptoms in about 10 days.

To date visual inspection of growing vines has been the only means available to determine trueness-to-variety. Unfortunately, experience has shown that even "experts" sometimes make mistakes this way. One way to improve accuracy is to have a number of "experts" look at the same vines in an established vineyard over a period of years. New biochemical techniques for grape identification work are being studied, but they are not available for use at this time.

Fortunately, once a vine is found to be true to variety and passes indexing tests, the variety and disease status do not change. Grapevines do not readily mutate to different varieties, and most virus diseases are transmitted only by grafting. Good nursery practices and careful record keeping will produce daughter vines of the same variety and with a disease status identical to the mother vine.

How can I be sure that my planting stock has been propagated from vines that were tested for disease and checked for trueness to variety?

At growers' request, the California State Department of Food and Agriculture (CDFA) developed the California Grapevine Certification Program to provide growers with a means for identifying grape stock propagated from virus-indexed and true-to-variety mother vines. Foundation Plant Materials Service (FPMS), at the University of California, Davis, is the repository for the virus-indexed, true-to-variety vines, and provides cuttings of these vines to nurseries participating in the Certification Program. State regulations require that all grape selections in the program test negative for specified diseases using specific indicators shown here:

Foundation stock from FPMS is labeled with a white certification tag and sold to California nursery participants in the Certification Program. Under the supervision of CDFA, Foundation stock is used by participating nurseries to plant registered field increase blocks. When cuttings from increase blocks are used to plant a certified nursery row, they are labeled with a purple registered tag. Rootings from a certified nursery row or cuttings from an increase block to be used for budding, grafting or planting directly into a vineyard are labeled with a blue certified tag.

Does a certified tag mean that the stock is true to variety and free of disease?

Buying certified stock is the best way to gain assurance that a serious effort was made to check the health and verify the variety of the stock. It is not, however, a guarantee that the stock is healthy or true to variety for several reasons:

• The indexing procedure used to qualify a candidate for the certification program does not detect every disease that has been or will ever be discovered because our knowledge of grape diseases and detection techniques is constantly improving.
• As noted above, objective methods available for identifying grape varieties at the University and elsewhere have not been perfected. Errors have occurred in the past at FPMS and may continue to turn up until a highly accurate identification method is available.
• The California certification program for grapevines is a voluntary program and much of the regulation compliance is voluntary in nature. Consequently, CDFA cannot guarantee that all procedures proscribed by regulation have been followed for stock labeled with registered or certified tags.

What additional information should I ask the nursery to supply stock I plan to purchase?

Growers can overcome some of the weaknesses of the certification program by taking a few extra precautions when buying stock. In addition to requiring California Certification tags, ask your nurseryman the following questions:

• What registered increase block did the rootstock and scion material for these plants come from?
• What are the FPMS selection numbers for the rootstock and scion material used to produce these plants?
• When were the source increase blocks planted?

The purpose of these questions is to establish a clear trail from the Foundation Vineyard at FPMS to the material to be purchased. If any gaps appear in this record, there is greater risk in using the material.

Can noncertified material be as good as certified stock?

Possibly.

Growers could privately conduct the same type of indexing treatment and inspection procedures FPMS uses to qualify a selection for the Certification Program and produce their own equivalent material. Costs for duplicating these procedures privately, however, could be prohibitive.

Material that has been propagated from currently registered certified stock with good nursery practices, sometimes called "first generation" or "as good as certified" material, should also have the same health and ID status as certified stock. Information needed in order to make this determination would include:

• Up-to-date information about which FPMS selections are currently registered -- this changes at least annually and sometimes more often.
• The history of the mother vine planting site -- if fanleaf-infected vines have been planted in the site in the last 10 years the material could be infected with fanleaf.
• Accurate information about rootstocks used, replants made and/or graftwood used for topworking vines in the source vineyard -- was it certified also?

By collecting this information a grower could reproduce part of the procedure employed by CDFA to certify grape stock. In addition, it would be important to ensure that there is a clear budwood trail from the Foundation Vineyard to the "as good as" source vineyard.

Treatments, tests and identification by the University, as well as supervised propagation and recordkeeping by CDFA, are the valuable although not perfect credentials of CA Certified Grape Planting Stock. FPMS therefore recommends that growers use CA Certified Planting Stock for which a clear trail from the Foundation Vineyard to stock purchased exists. Making the correct choice when choosing grape planting stock is crucial and no measure for checking it should be ignored. Using "as good as" or "first generation" stock is therefore a poor choice and is not recommended.

Who can I contact to get more information?

• California State Department of Food and Agriculture
  Nursery Service/Pest Exclusion
  1220 N St. -- P.O. Box 942871 Sacramento, CA 94271-0001 916-654-0435
• Foundation Plant Materials Service
  University of California
  Davis, CA 95616
  916-752-3590
• Your county grape farm advisor (University of California Cooperative Extension)