An opportunity to improve the quality of vines available to US winegrape growers
by James Stamp and Alan Wei
The California Grapevine Registration & Certification Program, administered by CDFA, aims to eliminate specific grapevine diseases such as leafroll, fanleaf, corky bark, stem-pitting and fleck that are spread from vine to vine by grafting and/or vegetative propagation1.
However, for many years, grape growers have been frustrated by the fact that CDFA certified grapevine nursery stock available from participating California grapevine nurseries are often found to be contaminated by these regulated viruses2-3.
The Grapevine Red Blotch associated Virus (GRBaV), described in fall of 2012 as the cause of leaf reddening and retarded ripening in wine grapes, helped growers to re-focus on the issue of cleanliness of their planting materials.
The availability of a PCR based diagnostic test for GRBaV confirmed that red blotch was widespread in both scions and rootstocks of CDFA certified grapevine nursery stocks. This led to the cancellation of shipment of unprecedented number of vines from California grapevine nurseries to vineyard sites all over the U.S.
Over the years, we have conducted field observations and laboratory testing of certified scion increase blocks which are the source of CDFA certified budwood for grafting. Increase blocks of important budwood clones were found to be contaminated with leafroll virus 3 and/or GRBaV.
We also found that finishing dormant plantings in CDFA certified nursery rows were contaminated with LR3 and/or GRBaV. While previously ordered nursery stock was cancelled because of LR3 and GRBaV contamination, growers still had to plant vines due to legal and economical considerations.
This led to a scramble to search/re-search and test/re-test copious volumes of scion and rootstock materials in order to find clean grafting stock. Through this process grape growers came to the painful realization that CDFA certified nursery stock could not provide them with clean grapevines free of economically important viruses (EIV), which was contrary to what they had expected.
Since spring 2014 an ad hoc committee of concerned growers and vine specialists was formed. The committee met regularly at Caldwell Vineyard in Napa with the goal of promoting changes in the CDFA regulation. Meetings were also held with CDFA, FPS and nurseries.
As a result of these activities, a public meeting was held in Sacramento in December 2014 where Joshua Kress, program manager of the CDFA’s nursery certification program, presented current requirements for testing, inspection, eligibility and traceability on foundation blocks, increase blocks and certified nursery plantings.
Current Disease Testing Frequency:
- Every Vine in Foundation block shall be retested by FPS at least once every five years for Fanleaf, Tomato Ring Spot, and Leafroll associated viruses
- Primary and Secondary Increase Blocks shall be tested by the CDFA at least once every five years for Fanleaf, Tomato Ring Spot, and Leafroll associated viruses
- Certified nursery plantings may be tested by CDFA for Fanleaf, Tomato Ring Spot, and Leafroll associated viruses
Current Inspection Frequency:
- Foundation Block – At Least two Visual Disease Inspections of each vine during each growing season
- Increase Blocks – At least one visual inspection by CDFA each growing season
- Certified nursery plantings – One visual inspection by CDFA each growing season, and stock is inspected at time of digging
Current Record-keeping/Traceability Requirements
- Maintain Inventory of All Grapevines Planted in Increase Blocks
- Maintain Records of vines removed from Blocks and reasons for removal
- Maintain Records of all vines that have been topworked
- Maintain Records of all registered and certified stock produced, sold, and/or traded for at least five years
- Provide any of the above records to CDFA upon request within 5 working days
- Identify/label registered and certified vines in the blocks with variety name and FPS selection number
Revision to the CDFA grapevine nursery certification program should include addition of GRBaV as a regulated pathogen and address defects in protocol that do not provide sufficient protection against easily vectored viruses. For example, the program currently calls for testing of key viruses every five years.
Given the widespread occurrence of mealybug, vectors of Leafroll 3 virus, the sampling frequency should be increased from every five years to every year. In addition, the program’s current sampling protocol for in-field increase block vines and finishing nursery stock is poorly defined and inadequate to provide statistically confident results.
Furthermore, the current program calls for visual inspection of all CDFA rootstock and scion increase blocks at least once a year. This is a critical step in securing clean material as visual evaluation of vines in fall can readily identify the presence of disease.
However, this is not a job for the untrained, and requires inspection of every vine at precisely the right time when symptoms are present. Top-work should not be allowed in the program. One of the biggest hurdles to development of an effective system is available funding.
It is imperative that the public search out the CDFA to comment on the existing program and that key industry stakeholders (e.g., growers, nurseries, FPS and CDFA) work together to develop an effective and transparent program, which will lay the foundation of clean grapevine planting stock for years to come.