Category: Vineyard Info

By Judit Monis, Ph.D.

Presently there are many laboratories that provide testing services dedicated to the detection and diagnosis of plant pathogens.  It can be confusing to the grower, vineyard manager, and/or nursery staff to decide which laboratory to choose.  My recommendation is to work with a plant pathologist who can provide guidelines towards the best option.  At the time, there is no accreditation that is specific for grapevine diagnostic laboratories in USA.  Therefore, each laboratory is free to develop their own testing and sampling methodologies.    

My expertise in grapevine disease diagnostics and my past work on developing state-of-the-art testing laboratories puts me in a position to evaluate the different choices for my clients.  The short answer is that there is no “one lab that fits all”.  In my experience, it is best to choose a lab based on the knowledge and capabilities specific to the needs of the project.  Generally speaking, choosing the lab because it offers the best prices or quicker turn-around-times might be a huge mistake.

This article will describe the different methods used for grapevine pathogen diagnostics and discuss the advantages and pitfalls of each of them.  Ultimately, I will attempt to convince the reader that the standardization of the diagnostic methods used for the detection as well the development of an accreditation of testing laboratories should be a goal for the future.

Different testing Scenarios

In an ideal world, the nursery or grower is interested in learning that their propagation and planting material is free of important pathogens.  But unfortunately, the grower may suspect disease in the vineyard due to specific symptoms.  Or as you may have heard me say many times, diseased vines may not always be symptomatic.  A knowledgeable plant pathologist will be able to help on statistical sampling as well as what type of laboratory is best suited for each case.  Regardless of the purpose for testing, below I will describe the most common methods available for the detection of important bacterial, fungal, and viral infecting pathogens.

Microbiological Culture

Fungal and bacterial pathogens can be cultured and isolated in specialized media (see fig.1).  However, microorganisms may compete among each other.  Generally, the microbe(s) with the most competitive growth capacity will overshadow microbes that grow slower, making the diagnosis difficult or even impossible.  In some cases, the diagnosis will be biased and a laboratory may not be able to report the disease causal agent unless sophisticated molecular methods are used (for details see NGS/HTS section).  Generally, in the case of the diagnosis of a declining vine in the vineyard or nursery, the identification of the fungal family (i.e., Diatripaceae species are associated with cankers) or bacterial genus (Agrobacterium species causes crown gall) may be sufficient to decipher the cause of the problem.  Phytoplasmas (a special type of bacteria that lack cell walls) and viruses cannot be cultured and their identification must be carried out using molecular and serological methods.

ELISA, PCR, RT-PCR, qPCR

The Coronavirus pandemic has made some of the terminology that I use in my articles much easier to explain.  The general media talks about antibody tests (ELISA is one) and PCR (this is a molecular test).   ELISA is the abbreviation for “enzyme-linked immuno-sorbent assay, and consists of sticking the virus coat protein on a plastic test plate that was coated with specific antibodies (Fig.2 Shows the loading of an ELISA plate in the laboratory).  A positive reaction is seen when there is a change of color in the wells of the test plate (colorimetric enzymatic reaction). ELISA detection is limited to the amount of virus present in the sample. PCR, is the abbreviation for polymerase chain reaction.  The technique allows the multiplication of viral nucleic acid from the initial titer (concentration) of pathogen present in the vine. The process is specific, and utilizes copies of small portions of the pathogen’s genome (called primers) to start the copying process. The amplification is repeated many times, with each copy making more copies, so after the completion of an appropriate number of PCR cycles, more than a billion copies of the nucleic acid is produced. For RNA viruses the detection is done using RT-PCR (RT stands for reverse transcription, a molecular way of converting RNA into DNA).  PCR and RT-PCR are sensitive techniques used for the detection of grapevine pathogens.  Quantitative or Real Time PCR is a modification of PCR that can provide the relative quantitation of the pathogen present in a sample (abbreviated as qPCR).

The sensitivity and specificity of the detection of pathogens can be influenced by the season as well as the part of the vine from which samples are collected. While ELISA is generally thought to be less sensitive than RT-PCR, ELISA has a broader spectrum of detection and can detect a range of virus variants. On the other hand, PCR is very specific, this can be an advantage but also a disadvantage.  If the detection is too specific, it could miss the detection of isolates of the same virus even when small changes (mutations) are present.  This is even more true when TaqMan, a type of qPCR that in addition to specific primers uses a specific probe is applied for the detection of viruses in grapevine samples.   This is why running both ELISA and PCR consecutively is recommended for the reliable detection of grapevine viruses, as each method is designed to detect different portions of a virus.   Since Grapevine red blotch virus is a DNA virus, and no ELISA has been developed as of yet, I recommend that PCR is performed to amplify at least two different portions of the viral genome.

Single Use Strips for “in house” detection

A molecular single use strip test has been developed for the detection of Grapevine red botch virus (GRBV) that claims it can be used for in-field testing.  However, for reliable results, the assays should be conducted by experienced technicians in a clean laboratory.  If a lay person were to attempt to run this type of assay, the instructions must be carefully followed.  The protocol includes many steps that are complicated and require measuring small quantities of reagents (microliters of components).   In my opinion, it is worthwhile to have an experienced laboratory run these tests.  Laboratory personnel are used to running different protocols and are trained to keep the sample and other materials free of contamination.  In the past, a kit was available for the “in house” detection of Grapevine leafroll associated -3 (GLRaV-3).  However, many different leafroll viruses can cause leafroll disease and obtaining a negative result for GLRaV-3 would have given the false impression that the vineyard block or sample in question was not infected.

Next Generation or High Throughput Sequencing

The next generation sequencing (NGS) also known as high throughput sequencing (HTS) is a powerful method that allows the laboratory to detect any organism present in a sample.

When NGS or HTS is applied, the complete sequence of the genetic material or microbiome present in the tested plant material or soil can be obtained.  Generally, during the sample preparation, the pathogens specific sequences are enriched to increase the sensitivity of the assay (for example the lab may just amplify fungal sequences).  The data obtained is analyzed with sophisticated software that is able to list the bacteria, fungi, virus, or other organisms (beneficial or pathogenic) present in the sample.  The method can provide relative quantitative data, generally expressed in percentages, of each organism found.   The NGS has been widely used in research and has allowed the discovery and characterization of important viruses such as Grapevine red blotch virus. Presently, this technique is being applied commercially to test plant and soil samples for the detection of bacterial and fungal microorganisms.  It is recommended that a plant pathologist with expertise in bacterial, fungal, and/or viral taxonomy be available to associate the presence of the microorganisms found with disease symptoms (or potential disease development).

Need for Accreditation of Laboratories

As mentioned earlier, at the moment, there is no accreditation system for laboratories performing grapevine diagnostic testing.  The closer we have gotten to these efforts is a ring (comparative) test run by the Lodi Wine Grape Commission.  A ring test consists in providing laboratories with “blind” samples of known infection status to determine if the laboratory’s in-house procedures are able to detect the correct infection status in each sample. In the past, while affiliated to various laboratories I was a participant of such ring tests.

In the fall of 2018, the Lodi Wine Commission ran a ring test to evaluate the different labs that offer testing for the diagnostics of grapevine viruses.   The laboratories received a large number of homogenized samples that were infected with various grapevine viruses.  The results of each laboratory were shared privately with the participant laboratories.  To the best of my knowledge no accreditation was granted.  While it is a great first step to carry out a ring test with the laboratories, future tests could be improved by providing the laboratory with portions of grapevines rather than a homogenized powder.  While it is understanding that homogenized samples may avoid the possibility of uneven distribution of viruses in the grapevine material, the capacity of the laboratory to process whole samples is important.  The integrity of the samples would determine if the laboratory is proficient on processing each sample without cross contamination or degrading the potential viruses present.

Conclusions

The standardization of the diagnostic methods for the detection of grapevine pathogens should be a goal for the viticulture industry in the near future.  The accreditation of laboratories is of upmost importance for evaluating the reliability of testing labs.  Standardization of sampling and testing is common in other fields of food and plant biotechnology.  It is puzzling that the grapevine industry has not adopted a system given the importance of this perennial crop.  My philosophy is that a vineyard must be planted with the healthiest available material as vineyards must live a long healthy life.  If a vineyard is planted with diseased material, its life expectancy is reduced (not to mention the possibility of perpetration and spread of pathogens in the vineyard and neighboring vineyards).

It is encouraging to know that new and more sensitive pathogen detection methods are being developed and applied for the diagnostic of grapevine pathogens.   The next generation sequencing or HTS is becoming more affordable and available for the detection at the species level of microorganisms in plants and soil.  It is expected that in the near future, these methods will be applied at the nursery and on new planting material to help develop healthy vineyards.

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.  During the Coronavirus pandemic, you can also schedule virtual vineyard consultations.  Please visit juditmonis.com for information or contact juditmonis@yahoo.com to request a consulting session.

By Dana Hinders

Most vineyards in North America and Europe will harvest grapes in August, September, and October. Typically, sparkling wine grapes are harvested first to ensure lower sugar levels, followed by the white wine grapes. Red wine grapes take a bit longer to reach full maturation, so they’re harvested later in the season. Finally, the grapes for ice wines make their way to crush, as it’s desirable they dehydrate on the vine to create a raisin-like grape with highly concentrated sugars.

  In most cases, a vineyard manager will check the grapes every day during the week or two before the scheduled harvest date because each part of the vineyard must be harvested at precisely the right moment. Matthew Clark, Assistant Professor of Grape Breeding and Enology at the University of Minnesota, says that understanding basic juice chemistry isn’t as difficult as it sounds. “The question is ‘Do I have enough sugar to make my wine product?’ Higher sugar grapes provide you with higher alcohol content in your wine. If there’s not enough sugar in your grapes, you can’t make wine without adding additional sugar. The best way to test sugar levels is with a handheld refractometer, either analog or digital. Each variety has a known point at which sugar levels won’t increase.”

  It’s usually preferable to harvest when temperatures are coolest. The cooler temperatures during the evening hours make grapes firmer and easier to de-stem, as well as creating better working conditions for those in the field. And, by harvesting at night, your grapes will already be closer to the temperature needed during the cold soaking process. “In order to reduce high fruit temperatures during harvest, which accelerates deterioration and demands more energy to cool fruit down further, harvest should be carried out early in the morning when temperatures are cooler or at night if a grower has sufficient lighting,” according to Elizabeth Wahle of the University of Illinois Extension Office. “Morning harvested grapes should be kept shaded until moved to a cooling unit.”

Choosing a Harvest Method

  Traditionally, all vineyards were harvested by hand. Hand harvesting gives you more control over the process and has the advantage of doing a better job of protecting the grape’s juice content from the oxidation caused by damaged skins. Mosbah Kushad, Postharvest Horticulturist at the University of Illinois, recommends hand harvesting if possible. “The biggest concern is fruit injury,” he said. “Damaged fruits enhance the rate of fungal and bacterial growth due to the seepage of their sugars. Damaged fruits also attract insects that could affect the quality of the finished product. For a small grower, hand harvesting is the way to go.”

  The main disadvantage of hand harvesting is the amount of labor required. If you can’t recruit temporary laborers or volunteers from the community, you may need to advertise on a site such as WineBusiness.com. However, Clark stresses that your labor force has to be flexible. “The biggest mistake I see smaller growers making is picking when labor’s available,” he said. “If you arbitrarily schedule harvest for Saturday and the grapes aren’t ready until the following Wednesday, you won’t happy with the results. Garbage in, garbage out is a computer science mantra with relevance to winemaking. For quality wine, you need quality fruit.”

  When hand harvesting, you’ll need to make sure your buckets are cleaned and sanitized before the big day. Sharpen your picking slips and lubricate them with a bit of olive oil. Provide cotton picking gloves for all your workers to protect against small cuts as well as the risk of bee stings.

  Mechanical harvesting is efficient and cost-effective. “Labor availability and quality is a big factor in choosing mechanical harvesting,” says Eric T. Stafne, an Associate Extension/Research Professor at Mississippi State University. “Economics is another. There is a certain economy of scale that makes it worthwhile to have harvest equipment. The market for the fruit may also dictate which method is used.”

  The mechanical harvest method works best for large vineyards that lay on a flat patch of ground, where the rows have been laid out straight, and the posts are of uniform height.  Additionally, harvesters shouldn’t be operated near ditches, embankments, holes, steep slopes, or within 15 feet of electrical wires.  Even for vineyards prepared with mechanical harvesting in mind, it’s always a good idea to do a pre-harvest survey for low hanging limbs, wires, or any obstacle that could obstruct the path of the harvester.

Post-Harvest Essentials

  As a winemaker, you want to avoid “reinventing the wheel” with each vintage you produce. This is why it’s crucial that you keep accurate records throughout the harvest process. Don’t expect to rely on your memory to recall the exact brix and pH you want or your average crop load per vine. Jot down relevant details on a notebook in your pocket or use a voice recording app on your smartphone. When the harvest is over, transfer everything to a spreadsheet so you’re ready for the following year.

  “At a minimum, records should be maintained to monitor vine balance: dormant pruning weights and yields are used to calculate crop load (Ravaz index),” Wahle said. “Over the years, this helps determine the impact of management and fruit quality. Yield can be estimated by keeping track of the number of vines per block, the average number of clusters per vine, and average cluster weights annually at harvest.”

  You’ll also need to tend to your field after your grapes have been picked. “Don’t forget the vines after harvest,” Stafne said. “They may need fungicide and insecticide applications to retain leaves, irrigation during dry periods, etc. to reduce vine stress and promote good health going into fall and winter. This will reduce chance for winter injury and encourage bud fruitfulness in the following year.”

  Vines should be pruned in winter when they are fully dormant. Without the leaves in the way, it’s easier to see the structure of the plant. When pruning, promptly remove and dispose of any diseased wood with lesions or sap, grapes that didn’t ripen, mold, and discolored leaves. Sterilize your pruning equipment by dipping the cutting blades in a solution of isopropyl alcohol after you’ve finished with each vine.

Harvest Time at Adelaida

  Located just 14 miles from the Pacific Ocean, Adelaida’s family-owned vineyards are in the mountainous terrain of Paso Robles’ Adelaida District. “We are one of the oldest wineries in Paso Robles, established in 1981,” explained Glen Mitton, winery and vineyard ambassador. “Our estate vineyards are planted between 1,650 ft. and 1,980 ft. We own the oldest continually producing Pinot Noir Vineyard in the Central Coast, planted in 1964. Our soil is a diverse combination of limestone, chalk, and clay with amazing water retention properties to enable us to dry farm 30% of our vineyards and also 100% of our 700 plus acres of walnuts.”

  The vineyards are farmed with Earth-friendly practices, which earned Adelaida the honor of being named a Certified California Sustainable Winegrowing Winery & Vineyard (CCSW) in 2015. “We pick our grapes based on flavors and condition of plant, as our winemaker is in the vineyard daily,” remarked Mitton. “We hand harvest all of our 157 acres of estate vineyards at night usually starting at midnight. Grapes are placed and transported from vineyard to winery in 20 lb. trays. While each year is different, we find our estate vineyard is a four to six weeks harvest process.”

Harvest Time at Laurita Winery

  Central New Jersey’s Laurita Winery is committed to creating wines that derive as much character from the fruit as possible. They pride themselves on being responsible stewards of the land, with 43 fully cultivated acres of vineyards and 200 acres of woodlands, meadows, and pasture. “We hand pick based on what varieties are ripe at the time,” noted Nicolaas Opdam, Oenologist/Vineyard Manager. “The process is monitored carefully. We take samples for two to three weeks to monitor sugar levels and pH. Since each grape variety ripens at its own pace, we usually have a few days between harvest sessions. This makes us fortunate to have a little flexibility in scheduling our labor force.”

  Laurita Winery employs staff members, their families or friends, and seasonal labor to pick the grapes. The pickers are taught to pay close attention to the vines, only picking the highest quality grapes. A second sorting occurs after picking to make sure damaged grapes or foreign material is removed. Opdam commented, “We’re an old school winemaker.  We watch the weather forecast and the condition of the vines carefully, but there’s a family feel to the whole harvest process.”

Harvest Time at Garvin Heights Vineyards

  In Winona, Minnesota, Garvin Heights Vineyards specializes in the growing of cold climate grapes developed by the University of Minnesota and Elmer Swenson. Made by cross breeding native American varieties with those from Europe, their grapes can withstand Minnesota’s colder temperatures while producing wine similar to what you might find in more traditional growing areas.

  According to co-owner Linda Seppanen, deciding when to harvest involves several factors. “Our primary chemistry considerations are the brix (sugar level) plus the acid level for the style of wine that we are intending to make,” she shared. “Along with this is when we can get a picking crew, what the weather will be, if we are having a lot of bird pressure even through the netting, and when the Asian Lady Beetles numbers are getting bad.”

  To find supplemental labor for their hand picking, Garvin Heights Vineyards enlists the help of local students. They also work with clubs that want to earn money for extracurricular activities, thereby streamlining the harvest process while also helping to support the community.

By: Becky Garrison

At the Oregon Wine Symposium held in Portland, Oregon from February 11-12, 2020, Dr. David Montgomery, MacArthur Fellow and University of Washington professor of geomorphology, presented his work researching and writing about farming methods that use less fossil fuel, fertilizer and pesticides than traditional farming. In his books, “Dirt: The Erosion of Civilizations” and “Growing a Revolution: Bringing Our Soil Back to Life,” Dr. Montgomery digs into the history of traditional farming methods and how these practices negatively impact the health of vineyard workers, the vigor of the soil and profitability.

  Dr. Montgomery advocates that, if we want to feed people in the next century, we need to change agriculture in this century. He cited the United Nation’s 2015 State of the Soil Assessment, which presented a global review of the world’s soils. According to this assessment, each year, the world loses 0.3% of net agricultural production capaci-ty to ongoing soil loss and separation.

  “If we play this out for the next hundred years, we are slated to lose about a third of our agricultural production capacity at a global scale. Our population is slated to rise by about a third,” Montgomery said. Furthermore, about a third of the world’s cropland has been degraded to the point where it’s no longer in production. 

The History of Soil Erosion

  While working on several continents, Dr. Montgomery noticed the connection between the degraded state of soils and the impoverished state of people living in different landscapes. He observed how soil erosion contributed to undermining civilizations around the world, starting with the earliest agricultural civilizations such as Neolithic Europe, Classical Greece, the southern United States Neolithic and more.

  In a review of over 1,500 scientific studies, soil erodes at the rate of one inch every twenty years. At this rate, the soil of a large civilization outside major river flood plains depletes in roughly 500 to 1,000 years. Dr. Montgomery described how flood plains like the Tigris and Euphrates bring sediment and silt, tires, school buses and whatever is coming down the river. “These places can maintain balance, as what the plow takes away on average is replenished by flooding. Nature is fixing the damaged of the plow.”

  His findings debunk the traditional theory of soil erosion found in environment history textbooks, that deforestation led to erosion, which undermined civilizations. “I found out it was the plow that followed that did it. The villain of this tale is tillage.”

  He described soil as akin to a bank account, whereby it is the natural capital that fi-nances civilizations, as it’s used to grow food, wine and everything else people grow from the ground.

  According to Dr. Montgomery, the plow leads to soil degradation because, by design, it inverts soil. “It provides incredibly good weed control, which is why it’s often used in organic systems. A plow takes those nasty weeds upside down and makes fertilizer out of them.”

  In addition, tillage accelerates the breakdown of the organic matter in the soil by stimu-lating microbial activity. In effect, this draws down the batteries of the soil by degrading its organic matter. Also, tillage leaves the soil vulnerable to erosion until the next crop. If this process goes on for long enough, the soil’s organic matter can deteriorate to the point of impacting the fertility of the land, negatively affecting the health of the crop.

Is Soil Restoration Possible?

  “The problem with long-term soil degradation is not that we farm. The problem is the way we’ve been farming. Tillage has been a major destructive element in human histo-ry,” said Dr. Montgomery.

  While traditional farming methods account for the loss of a millimeter to a millimeter and a half of soil each year, no-till farming only erodes less than a tenth of a millimeter of soil during the same period.

  When Anne Biklé, Dr. Montgomery’s biologist wife, turned their degraded yard into a garden, she added organic matter consisting of compost and mulch. After a decade, their yard went from 1% organic matter to 12% in some places. In their book, “The Hidden Half of Nature,” they attributed this shift to the work done by trillions of micro-organisms that were feeding underground. This zone, called the rhizosphere, is one of the most life dense areas on the planet. Dr. Montgomery described the rhizosphere as “a biological bazaar where microbes and plants trade nutrients, metabolites and exu-dates.” Like any living organism that consumes something, the plants metabolize the organic matter and produce waste products like growth hormones.

  Understanding the symbiotic relationships between soil microbiota and plants presents farmers with two very different diets for feeding their plants. The first is the fertilizer diet, where if you give a plant enough fertilizer, even bad soil can produce big yields. How-ever, as Dr. Montgomery assessed, once the plants get all the significant elements they need for growth, they stop investing in their root system. “This means they’re not get-ting as many micronutrients, like zinc and copper, that they need for health, which those microbial partners provide.”

  In comparison, growing plants in healthy, fertile soils that have more organic matter to feed those microbes will produce comparable growth. In addition, farmers get the ben-efits of mineral micronutrients and microbial metabolites. Simply put, organic matter produces higher carbon in the soil.

Principles of Conservation Agriculture

  To assess if these theories could be implemented on a large scale, Dr. Montgomery visited farms in Equatorial Africa, Central America and all across North America. What he found was a common recipe for rebuilding soils.

  First, he said, ditch the plow. Minimal tilling can produce better results, but more car-bon generates when not using a tiller. Second, cover up the soil by maintaining perma-nent ground cover using cover crops and retaining crop residues. Finally, grow diversi-ty. Rotating three to four crops will break up pathogen carryover. In a vineyard, one can achieve this by rotating what’s growing between the vines.

  According to Dr. Montgomery, these principles could be scaled up or down, depending on the farm, within two decades. Restoring agricultural soils in this manner can help increase farm profitability, feed the world, help with climate change and prevent envi-ronmental degradation through non-chemical practices.

How Microbes Relate to the Wine World

  Discussions about terroir focus on climate and soil; however, Dr. Montgomery sug-gests rethinking terroir in terms of the microbes, which are related to climate, soil and geology. “As we examine the relationship between the soil, the vines and the wines people enjoy, we should think about how the microbial ecology is a big part of that foundation.”

  Recent journal articles have begun to cover the landscape of microclimates, including those of a particular vineyard. Microclimates affect the microbes that live in the rhizo-sphere around the roots of grapevines and can carry through to the winemaking pro-cess.

  “Microbial abundance and diversity come into play on leaves, roots and fruit, and then carries on into the fermentation process. How you operate your vineyard will determine what you will have in terms of the fungal community,” said Dr. Montgomery. “Hence, understanding the role of microbial ecology is important for rebuilding soil organically, but also in understanding every step of the wine production process.”

  Addressing the practicalities of soil management in the vineyard, Dan Rinke, proprietor of Roshambo ArtFarm and Director of Vineyard Operations at Johan Vineyards, said, “If you are continuously tilling and depleting organic matter from the soil, those resultant soils are going to be more prone to compaction. But you can have more resilient soil through no-till systems.”

  In Rinke’s estimation, the best way to rotate cover crops is to use a no-till seed drill, which can be rented from some soil and water conservation districts. However, he added that he’d like to see research done in this area to see more comprehensive re-sults using conventional, reduced and no-till means specifically for vineyards.

  More research is needed to confirm Dr. Montgomery’s findings and develop and under-stand the implications for vineyards. For biodynamic farmers like Barbara Steele of Cowhorn Vineyard & Garden, carbon farming is not unique. “Carbon cycling in the soil is the basis of successful dirt farming,” she said.

  Biodynamic practices include building a fresh compost pile every year and growing plants whose sole purpose is to create carbon. “By increasing organic matter in the soil, we slowly increase the cation exchange capacity or CEC (the measure of the soil’s ability to hold positively charged ions), and thus the carbon cycling in the soil,” said Steele.

  For more information about soil health, check out the resources available from the USDA National Resource Conservation Service at…https://www.nrcs.usda.gov/wps/portal/nrcs) and www.dig2grow.com

By: Judit Monis, Ph. D.

As I write this article, the world is experiencing the SARS-COV-2 pandemic responsible for causing COVID-19 disease.  Generally, I find it difficult to explain quarantine measures.  Today, I am sure that all of my readers might had practiced some sort of “sheltering in place” or “social distancing”.  Therefore, the concept of quarantine will feel closer to home at this time. I am revisiting the quarantine and certification topic as this time; it is expected that my audience will be more receptive to the concepts.

Years ago, when I worked at the United States Department of Agriculture – Animal and Plant Health Inspection Services- Plant Protection and Quarantine (USDA APHIS PPQ), my group learned about the interception of citrus cuttings (intended for planting) that were packed pretending a box of chocolates was in the shipment.  I am sure that you have heard before about “suitcase clones”.  These are grapevine clones that people have brought from abroad before or after quarantine measures were developed  It is my hope, that what we learned about the introduction and spread of SARS-COV-2 world-wide will provide a lesson to people to think twice before breaking the law by introducing plant material without import permits or respecting quarantines. 

  Plant quarantine programs have been developed worldwide to reduce the risk of introducing plant pests and/or pathogens that do not occur in a country or region.  My expertise is plant pathology and throughout my career I have specialized in the study of bacteria, fungi, and viruses that affect the vineyard and fruit orchards.  In spite of the current existence of plant quarantine programs, all grapevine pathogens with rare exceptions occur in all grape growing areas worldwide.  The reason for this is that in most cases, quarantine programs were implemented after the introduction of the infected plant material.  In addition, modern techniques for the detection of these pathogens were developed after the plant material was introduced. In other words, the majority of grapevine pests and pathogens were moved unknowingly. 

  The advancement of science and the use of sophisticated detection methods for grapevine pathogens has helped keep certain viruses outside of Australia.  For example, Grapevine fanleaf (GFLV) and Grapevine red blotch viruses (GRBV) have not been reported in Australia as of yet. But even now with the use of advanced methodologies, pathogens continue to be discovered. As science progresses with the development of more refined technology (e.g., next generation sequencing also known as high throughput sequencing), it is expected that new (or unknown and established) pathogens will be discovered. In practice, most grapevine pathogens have originated at the centers of origin of the Vitis (a plant genus that includes both table, wine, and rootstock grapevine varieties) species and moved to many grapevine growing regions in the word when plant material was introduced. 

  In the United States, the USDA APHIS PPQ regulates the introduction of plant material for planting from foreign countries.  However, the USDA does not have a centralized government plant quarantine system.  Instead, APHIS issues permits to specific clean plant centers with proper containment facilities and approved protocols to manage the quarantine of specific crops. For grapevines, two import centers are available for introducing quarantined planting material: The Foundation Plant Services (FPS) at the University of California at Davis and the Clean Plant Center at Cornel University in Geneva, New York.  

  Since pathogens are present in most grapevine growing areas, certification programs are needed to produce tested plant material that is free of known important pathogen.  These plants are be distributed to nurseries that further propagate and sell them to growers.   In the United States, certification programs are voluntary and are managed by individual states.  I am most familiar with the certification program in California, and many US grapevine growing regions purchase planting material from California nurseries. 

  The Grapevine California Registration and Certification (R&C) Program was first written into law in the 1980’s.   The Grapevine R&C Program is administered by the California Department of Agriculture (CDFA) and provides for the testing of source vines for grapevine viruses that cause important diseases. Registered sources and certified nursery stock are periodically inspected by the CDFA staff and are maintained by the participant nurseries.   Starting in 1996, I participated and provided input at the industry meetings that lead to the revision of the California Grapevine R&C program many years later.   In 2010 the Grapevine R&C program was revised to include testing of foundation mother vines for the presence of a comprehensive list of viruses. With funding from the National Clean Plant Network, a new of foundation block “Russel Ranch” was started at the University of California at Davis in 2009.  

  The planting material (both scion and rootstock varieties) included in the new foundation block had to pass a rigorous testing program and have been propagated using the “apical micro-shoot tip culture” technique.   The apical micro-shoot tip culture process is a plant tissue culture technique that is used to eliminate pathogens from vegetative propagated plant material.  The testing program is known as Protocol 2010.  The maintenance and testing of the scion and rootstock mother blocks are performed by UC Davis FPS personnel.  Shortly after the update of the California Grapevine R&C Program, GRBV, a virus of significant importance for the vineyard industry, was discovered.  Consequently, the California Grapevine R&C Program was revised again to include the testing of foundation and nursery increase blocks for the presence of GRBV.  

  The California Grapevine R&C Program rules can be found in CDFA’s website:  https://www.cdfa.ca.gov/plant/pe/nsc/nursery/regcert.html

  The testing of the foundation mother plants includes a list of well characterized viruses, Xylella fastidiosa, and phytoplasmas using biological, serological, and molecular testing techniques (https://fps.ucdavis.edu/fgr2010.cfm).  The nursery increase blocks are inspected and tested by CDFA personnel.  The nursery increase blocks are only tested for GFLV, Tomato ring spot (ToRSV), and Grapevine leafroll (GLRaV)-1and -3 using the Enzyme linked Immuno assay (ELISA). The updated Grapevine R&C added the testing for the detection of GRBV using the polymerase chain reaction (PCR) to vines in the foundation and nursery increase blocks. 

  Unfortunately, other insect vectored viruses such as GLRaV-4, Grapevine virus A (GVA), GVB are not being tested at the nursery.  Related to nursery certified plants, the rules are vague and state that these plants may be tested (particularly if after inspection suspected symptoms are observed). 

  According to CDFA, the goal is to test a statistical sample with a 95% confidence level assuming a 1 % disease incidence.  It is disappointing that in spite of the importance of the decline and canker diseases caused by fungal pathogens (and how easily the pathogens can be transmitted by activities carried out at the nursery), the regulations do not include inspection or testing for fungal pathogens in mother or increase blocks.  

  In the past few years, the Russell Ranch foundation block became progressively infected with GRBV.  The infection status is so high that last year FPS suspended the sale of plant material to nurseries.  I will not elaborate on this issue as I have recently written about this topic.

  Obviously, in spite of the limitations of the R&C program mentioned above, the use of certified material is expected to be less risky than planting field selections of unknown infection status.  However, it is always prudent to consult with me to assure that the planting material meets the expected cleanliness standards.

  An important piece of advice when working on the procurement of clean planting stock is to plan in advance.  Most nurseries in California collect cuttings for bud wood as soon as the vines are dormant.  However, grafting activities are performed during the spring of the following year.  Planning with time will allow for inspection of the increase blocks early in the fall before a freeze.   Being familiar with the nursery’s operations and their staff is important.  Good communication will help with scheduling inspections and testing of the increase blocks from which bud wood and rootstock cuttings will be collected. 

  Diseases, pathogens, and/or their vectors do not know or respect the borders between vineyard blocks (at the nursery, foundation block, or your vineyard).  Even if the planting material came from a reputable certification program, paying attention to the surrounding vineyards as well as having knowledge of the potential presence of disease prior to planting is important. 

  The planning of a new vineyard is not trivial and requires specialized knowledge.  I am available to help look for suspicious symptoms (inspect scion and rootstock source blocks), evaluate the planting site, develop a testing plan based on science and statistics, and review nursery and vineyard disease testing history.  

  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 or virtually.

By: Dr. Richard Smart, vinedoctor@smartvit.com.au, www.smartvit.com.au

Where is the best place to grow wine grapes,” I am often asked. The answer I give surprises many people. I say, “A cool desert, that is where! Deserts are typically sunny, but should be cool, and with sustainable supplies of irrigation water.” A desert is preferred because rainfall can be a problem for quality wine production.

  There are two significant problems associated with rainfall, both relating to how difficult it is to control, in terms of timing and quantity. Firstly, rainfall induces many fungal diseases on leaves, shoots and fruit, which may have direct or indirect effects on fruit ripening and wine quality. Secondly, and often less appreciated, is that water supply is a principal means of regulating vine growth and physiology to maximize fruit ripening and potential wine quality.

  In brief, we prefer to have slight moisture stress during the period of active shoot growth after flowering to inhibit lateral shoot growth and to limit leaf expansion and size. In association with an appropriate training system, this will help maintain a light, porous canopy—essential for wine quality. Secondly, and critically, we can use moisture stress to stop shoot tip growth in the period just before veraison. This is essential to avoid carbohydrate competition between the active growing shoot tip and the ripening berries.

  If grapes are grown in a desert, of course, we need to irrigate. This gives us a chance to manipulate vine water stress at our will, in the absence of rainfall. The rest of this article discusses how to manage the desired level of water stress.

Irrigated Vineyards

  Irrigation research was one of my first projects when I started a viticulture career in the mid-1960s in Australia. Then, drip irrigation was very new, and I published one of the first studies on the method with wine grapes, comparing drip to flood irrigation.

  This was also a time of new technology for measuring plant and soil moisture. Gypsum block and tensiometers were common then, and soon soil capacitance meters were to be introduced to measure soil moisture.

Evaluating the Pressure Bomb

  In the late 1960s, pressure bombs used to measure leaf and stem water potential were introduced. The pressure bomb was a powerful tool to directly measure plant water stress, and help understand how grapevines respond to soil moisture conditions and the daily pattern of weather conditions.

  After sunset, grapevines recover gradually from the water stress of the day before. Then, at sunrise, the plants begin to experience mild water stress. As air temperature increases, and as humidity decreases, so water stress experienced by the plant increases, being at a maximum in early afternoon. As sunlight levels decrease towards late afternoon, the water stress experienced by the grapevine recovers somewhat, again declining substantially after sunset.

  Our published studies determined a major impact of current weather conditions on grapevine water stress. Grapevines experience the most water stress with bright sunlight, high temperatures, low humidity and high wind speed. These are all conditions that cause the most rapid water loss from the vines.

  As soils dry out, the level of plant water stress is higher during the morning and in the afternoon. However, one must be careful to distinguish the effects of soil moisture from those of higher sunlight, temperature, wind speed and lower humidity. It is challenging to take spot measurements with the pressure bomb during the day to predict soil moisture conditions. Direct measurement of soil moisture profiles is preferred, which are much less variable over the day.

Use of Plant Appearance

  I had almost side-by-side vines with different soil moisture conditions in an irrigation trial I conducted, and I soon learned how the appearance of vines change as they develop water stress. One of the most obvious symptoms is that shoot tips stop rapid growth, and eventually, they stop growth altogether. This symptom relates to moisture stress over several week’s duration.

  Another of the visual effects of water stress is on leaf inclination. Initially, the petioles droop a little, and as stress continues and becomes worse, the leaves first hang vertically and then begin to cup by folding inwards along the main vein.  When very stressed, you will see the backs of several leaves if you look along the row. I was working with the Shiraz (Syrah) variety, and the leaf backs are hairier than the front, so they are easy to distinguish. These symptoms may take several days or a week to develop.

Leaf Temperature Assessment

  This assessment relates to present vine water stress. When vines are water-stressed, stomata (leaf pores controlling water loss on the leaf underside) partially or fully close, and so the loss of water from the leaf ceases. Transpiration (like evaporation) acts to cool leaves. So a sunlit leaf will have a temperature not so different from that of the air, perhaps a little warmer or cooler. However, when the vine is water-stressed, sun-exposed leaves are noticeably hotter than air temperature because the stomata close, and shade leaves are around air temperature.

  I proposed a leaf temperature-based water stress index, which is in Table 1 (Below).  Measurement is suggested in the early afternoon, or when it is sunny and air temperature reaches its maximum. Mid-shoot leaves well exposed to the sun are tested. I suggest pressing the leaf blade between fingertips and palm and quickly sensing leaf temperature on the palm. One must take an instantaneous impression of leaf temperature, as holding a leaf will quickly bring its temperature to that of your hand!

  The reader might be thinking, “Why not use an infrared thermometer to measure air temperature as we have seen used recently to indicate forehead temperature with Covid-19 virus detection?” Indeed, such devices are now quite cheap, portable and accurate, but be careful always to measure leaves with the same angle to the sun.

Conclusion

  Leaf temperature will give an instantaneous measure of vine water stress. In contrast, leaf inclination and shoot tip growth assessment will indicate water stress over the previous two weeks or longer. Therefore, leaf temperature can give a better indication of water stress, and so, irrigation needs, while shoot growth will advise how effective the irrigation has been.

  The clever vine irrigator might believe these visual guides more than those of randomly taken pressure bomb tests to manage vineyards to optimize wine quality. Modern irrigation monitoring is developing systems based on thermal images, either close up or remote, related to my simple system of using one’s hand!