By: Judit Monis, Ph.D.
This year I was invited to do a presentation at the Southern Interior Horticultural Show in Penticton, British Columbia (Canada). The growers in British Columbia are experiencing problems due to diseases and need to replant their vineyards. I was so glad that my audience was interested in plant health and procuring material that is not infected with pathogens (disease causing agents). There are so many articles and books that focus on planting a new vineyard. These describe soil preparation, setting up irrigation, trellis systems, etc. but rarely focus on plant health. The best way to avoid disease in a vineyard is prevention. It is known that diseased plants are more susceptible to environmental stress such as heat, cold, drought. Further, once infected vines are planted, it is too late to fix the problem. In this article, I will describe guidelines and best practices to assure that the vineyard planting material is healthy and remains healthy during its lifetime.
Available Nursery Material
In the spring. Nurseries are busy grafting the cuttings of rootstock and scion varieties that were collected in the winter. Most nurseries in California propagate and grow material from the California Certification and Registration (R&C) program. This R&C program was revised in 2010 to include testing for specific pathogens (mainly viruses and Xylella fastidiosa, the causal agent of Pierce’s disease). After the discovery of Grapevine red blotch virus (GRBV), the regulations were revised once more in 2016 to include the exclusion of this detrimental virus in the certification program. Canadian growers procure plants from the Canadian Certification program but also purchase plants from California nurseries.
Some growers and winemakers already have a favorite nursery they have worked with and have had good success with the planting material. Others may had had a bad experience and likely will avoid working with that nursery. In every case, it is important to develop a good working relationship with the nursery that will produce the grafted vines to be purchased. Prior to placing an order, there is important information to request from the nursery that will help determine the quality and health of the plants they produce.
Most growers will be interested in purchasing certified grafted vines as they have an extra level of assurance (the foundation mother blocks are tested regularly for certain pathogens). However, growers must be aware that grapevine plants are still being propagated in nurseries from the old California R&C program (material from the early 1980s Since many diseases are transmitted and spread in the vineyard you can expect that the older the block the higher the chances of being infected with one or more pathogens!). It is also important to know when was the nursery increase block planted. As starting in 2017, the new U. C. Davis foundation block was found to be progressively infected with GRBV to the point that it had to be abandoned and replaced with plants grown in greenhouses.
Even if the nursery propagates material from the certification program you should ask if the nursery has a disease testing and sanitation plan. The nursery personnel can provide their quality assurance protocol. Questions to ask include the following: how old are the mother blocks? how many vines are tested in each block? Does the nursery perform random testing or do they have a plan and test all vines on a rotation basis? Which pathogens are tested for, how often, and why do they not test for others? Do they test single vines or composites of many vines? What do they do when a composite sample tests positive for a detrimental virus (i.e., Grapevine leafroll, fanleaf, or red blotch)? Would they allow you or your consultant to take samples of the varieties or clones of interest and base your purchase on the laboratory results? The answers to these questions will reflect the seriousness of the nursery operation and give some idea of the overall health of the increase blocks and nursery rows. In addition, I strongly recommend to request reports of the analyzed vines to learn about testing schedules and health history of the nursery’s increase blocks. If the reports are not clear, talk to the nursery personnel or a plant pathologist to help you understand the testing schedule and/or results. It is important to visit the grafting and propagation facilities to perform your own inspection. Finaly, inspecting the plant material and performing a random test prior to delivery and planting will avoid planting material infected with trunk disease causing fungi and Allorhizobium vitis (previously known as Agrobacterium vitis, the causal agent of grapevine crown gall). If you do not have the required knowledge to understand what to look for, I recommend you hire an expert who can help.
Testing Requirements of Plant Material
To increase the assurance of freedom of disease, representative samples from blocks of the rootstock and scion material should collected and submitted to a testing laboratory to determine their health status. If the vines are field finished (i.e., not potted), testing after growing in the nursery rows or after cold storage is recommended to assure freedom of disease-causing agents. Is it possible to develop a testing plan depending on the number of vines to be produced, either by testing individual mother plants or using statistical sampling. The more samples that are submitted for testing, the better confidence in results.
The grower may decide to propagate and graft material from their own or a neighbor’s vineyard. This choice can be based on early performance of the specific variety or clone in the winery. However, caution must be taken to assure that the field selection is not infected with detrimental pathogens. A field selection that performs well in one vineyard may not perform the same way in a newly planted vineyard. For example, it is known that some pathogens may not display symptoms until a stress factor is present. Also, some varieties display more symptoms when grafted to a specific rootstock. In summary, regardless of where the plants originate, it is a good practice to test the mother vines for the presence of pathogens.
Prevention of Infection in the Newly Planted Vineyard
Procuring certified and/or disease-free tested vines, is just the start. The newly planted vines have the potential to become infected during their life span. This is especially possible if a diseased vineyard block was removed and replaced with “clean planting stock” or nearby blocks are infected with a virus that is able to spread (e.g., some Grapevine leafroll associated virus species are transmitted by mealybugs; Grapevine fanleaf virus is specifically transmitted by nematodes).
The new blocks and adjacent vineyards should be monitored for insect vectors and/or suspicious symptoms. It is always a good idea to determine the cause for suspicious symptoms as viruses and other pathogens can spread from adjacent vineyards. The knowledge of a positive finding of a virus that is transmissible and the presence of the insect that transmits it will turn on a warning sign. For example: Grapevine leafroll associated virus-3 or other related Ampeloviruses (GLRaV-1, or -4) and the mealybugs that can transmit these viruses should alert the vineyard manager of a disease prevention strategy that will help avoid the spread of these viruses. I have observed instances in which a vineyard owner removes (and replaces with tested vines) only half of the infected vineyard block to avoid production losses.
A new vineyard planted with vines infected with Allorhizobium vitis (cluse up)
The other half of the infected vines are removed after the newly planted vineyard block starts to produce grapes. This is not recommended. In these cases, I have seen that by the time the infected older plants are removed, the newer plants have become infected with the same pathogens that were present in the original block.
Some important fungal and bacterial pathogens are soil-born and can be transmitted to the new planting after the infected vines were removed. But it is also possible to bring these pathogens with the new planting material. In many cases, a simple visual inspection can indicate that the planting material is infected with A. vitis. Either way, with no symptoms present, sophisticated tests are available to test the vineyard soil and planting material to allow the grower to make informed decisions on planting and disease management.
Conclusions
In summary, new vineyard development is a critical task that should be taken seriously. My recommendation is not to hurry. Do not just purchase the only material left at the nursery or propagate your next-door neighbor’s budwood because you made last minute decisions. Take the time to make sure that the planting material will meet the quality standards that will produce the best grapes for optimal wine or table production. You probably heard me say many times that the only way to avoid disease in the vineyard is to prevent the introduction of harmful pathogens.
By far the most efficient way of pathogen introduction in a vineyard is by planting material that is already infected (one infected mother plant can produce 200-300 infected daughter plants!). Currently there is no cure for graft-transmissible diseases once established in the vineyard. This urges you to apply special care when selecting planting material prior to developing a new block. With these simple guidelines, it is my hope that you will develop a vineyard that will be healthy and productive.
Judit Monis, Ph.D. provides specialized services to help growers, vineyard managers, and nursery personnel avoid the propagation and transmission of disease caused by bacteria, fungi, and viruses in their vineyard blocks. Judit (based in California) is fluent in Spanish and is available to consult in all wine grape growing regions of the word. Please visit juditmonis.com for information or contact juditmonis@yahoo.com to request a consulting session at your vineyard.
