Category: Vineyard Info

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!

PR For Release: 6/1/20

In helping to lead the defense against PD, Carter Creek Winery Resort & Spa, located in Johnson City in the heart of the Texas Hill Country, has just planted more than seven acres of Pierce’s Disease (PD) resistant vines from Wonderful Nurseries. After several years of preparing and working with UC Davis to obtain licensing to sell the vines, Wonderful Nurseries delivered the first batch this spring and will continue to grow these PD resistant vines and supply them to growers throughout the United States.

Caused by the bacterium Xylella Fastidiosa, PD has become a common scourge for grapevines and the grape growing industry at large. Carter Creek winemaker Jon McPherson noted that, as one of the country’s first vineyards to plant the PD resistant vines, a new day may be dawning for growers everywhere in large part due to this transformational breeding project spearheaded by Andy Walker, Ph.D., Genetics, University of California at Davis. “With these new vines, our Texas estate vineyards will now be 100 percent Pierce Disease-resistant,” said McPherson.

Wonderful Nurseries, growing one success after another, is proud to play a part in this game-changing industry innovation. These newly planted vines; the Walker Clones of Paseante Noir and Errante Noir are both red grape varieties with ample balance. Offered too are Camminare Noir (red) and two white varieties, Ambulo Blanc and Caminante Blanc.

Carter Creek Winery Resort & Spa is a new winery resort in the rolling hills of the Texas Wine Country with tasting rooms, an onsite microbrewery, outdoor event center and 78 guest villas, owned by Carter Hospitality Group, LLC. This is the same team that owns and manages award-winning South Coast Winery Resort & Spa, in Temecula, as well as many other wine and hospitality establishments.

It’s always “Growers First” at Wonderful Nurseries, whether it’s PD-resistant grapevines or any number of industry innovations. For more information call Wonderful Nurseries at (661) 758-4777 or visit their website at WonderfulNurseries.com.

By: Judit Monis, Ph.D.

You probably know that I worked and developed several grapevine disease detection labs in the past.  Now I am on the other side and am able to choose the lab that is able to fir with the needs of the specific project I am working on and evaluate their practices.

  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 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 for grapevine diagnostic laboratories in USA.  Therefore, each laboratory is free to develop their own testing and sampling methodologies.  

  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 accreditation of testing laboratories should be adopted by the grapevine industry

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, many times, the grower may suspect disease in the vineyard due to specific symptoms.  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.  However, microorganisms may compete among each other.  Generally, the microbe(s) with the most competitive growth capacity will overshadow slow microbes that grow slower, making the diagnosis difficult or even sometimes 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 (see NGS/HTS section).  However, 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, and RT-PCR

  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.  The detection can be 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 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 = a copy of the viral RNA via reverse transcription) before PCR can start.  PCR and RT-PCR are sensitive techniques used for the detection of grapevine pathogens.

  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, the ELISA has a broader spectrum of detection but is available only for grapevine viruses and can detect a range of virus variants. On the other hand, PCR can be too specific, and miss the detection of isolates of the same virus even when slightly different. Using both ELISA and RT-PCR consecutively is recommended to reliably detect grapevine leafroll viruses, as each method is designed to detect different portions of a virus.

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 can be used for in-field testing.  Although, this test is marketed for use in the field, for reliable results, the assays should be conducted by experienced technicians in a clean laboratory.  If a lay person were to attempt to run the assay, they the instructions must be carefully followed, as the steps are complicated and require measuring small quantities of material (microliters of components).   In my opinion, it is worthwhile to have an experienced laboratory run these tests.  It is expected that laboratory personnel 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 associated virus. Presently, this technique is being applied for the commercial testing of plant and soil samples to detect bacterial and fungal microorganisms.  A plant pathologist with expertise in bacterial, fungal, and viral taxonomy is able 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 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 pathogens.  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, the 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 on new planting material and 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.  Please visit juditmonis.com for information or contact juditmonis@yahoo.com to request a consulting session at your vineyard.

By: Tracey L. Kelley

  Spring pruning is one of the most vital applications vineyard managers can control, so it’s always beneficial to cross-check your processes with an expert or two. Depending on the air temperatures in your region, you might be edging into budburst (also referred to as budbreak) right now, and believe most of your pruning is complete.

However, according to Fritz Westover, owner of Westover Vineyard Advising and Virtual Viticulture Academy in Texas, there are always reasons to examine the results of pruning not only at the start of the season but also throughout, to understand what worked and what should be remedied. Watch helpful instructional pruning videos from Fritz Westover.

  “I do a lot of post-pruning site visits with growers, and it’s always informative to learn what you did wrong after you did it!” Westover joked. “The number one mistake I correct is the retention of small wood, followed by the retention of too many buds per vine. Both can result in an inefficient canopy, poor fruit quality and overall less balanced vines. The good news is that it’s easier to take buds off than to put them back on.”

Spur and Cane Pruning: Reasons for Each

  “Ideally, the decision to spur or cane prune should be made before designing and planting a vineyard,” Westover said. “However, most varieties can adapt to either a cane- or spur-pruned system. Also, I’ve found both vertical shoot positions or high-fruiting wire training systems can adapt to spur or cane pruning.”

  “A lot of our decisions regarding spur vs. cane pruning is based upon varietal,” Kim Myers told The Grapevine Magazine. Myers , co-owner, Laurel Gray Vineyards and Yadkin Valley Wine Company, along with her husband, Ben, co-stewards land in North Carolina that’s been in the family for 10 generations. Their 10.5-acre vineyard, Laurel Gray, features estate French vinifera vines such as Chardonnay, Viognier, Pinot Gris, Merlot, Cabernet Sauvignon, Cabernet Franc and Petit Verdot. Their winery, Yadkin Valley Wine Company, produces award-winning selections, including a signature Bourdeaux blend, Scarlet Mountain; Estate Barrel Fermented Chardonnay; and Estate Cabernet Sauvignon, Merlot and Viognier.

  “Spur pruning is used for varieties that show high fruitfulness on basal buds. For example, Cabernet Sauvignon works very well on spur pruning—until it’s time to renew the cordons. When renewing, we cane prune in order to establish a new healthy cordon,” she said. “Viognier produced best when cane-pruned because this technique allows more light on to the cordon and into the canopy.”

  “Generally, spur pruning, once established, is less labor-intensive. It’s easy to do and easy to teach, especially for vines that are trained on fences or trellises,” Myers added.

  Westover provided further recommendations. “In general, sites that require in-row vine spacing wider than four feet are better adapted to a cordon/spur-pruning system to best utilize the space in the fruiting zone, as laying canes longer than 18-24 inches can result in poor shoot size uniformity in many varieties,” he said.

  “Cane pruning, on the other hand, results in a vine that has a lower number of pruning wounds than a vine that is spur-pruned. Therefore, there might be less opportunity for certain fungal diseases that infect pruning wounds and cause grapevine trunk diseases,” he said. “Additionally, there’s less old wood on a cane-pruned vine and less potential area for disease spores to overwinter, such as phomopsis or other GTD-associated pathogens. Some varieties are also known to be more fruitful when cane-pruned, such as Nebbiolo or Malvasia Bianca.”

  “Cane pruning requires a high level of expertise, is more expensive and takes more time,” Myers added. “You have to make very educated choices about each and every vine. However, cane pruning has many advantages: frost protection, even production and even spacing of growing shoots in the spring.”

  Similar to what Myers does at Laurel Gray, Westover incorporates both methods for individual vines on some of his clients’ properties. “This isn’t typical, but can help increase the yield on vines that have high vigor but low yields due to small cluster size or shading of lower bud position of the spurs,” he said. “Careful consideration should be made as to where to use this practice, as the extra buds can cause crowding in the canopy, which can increase disease pressure in wet, humid climates.”

  Another mitigating factor for following a pruning method is the rumbling advance of mechanized or “no-touch” vineyard operations. The University of California Agriculture and Natural Resources Department released data in 2019 from a 53-acre Merlot research vineyard in the San Joaquin Valley—where more than half of all California grapes are grown— that indicated mechanical pruning “reduced labor costs by 90%, resulted in increased grape yields and had no impact on the grape berry’s anthocyanin content.”

  Kaan Kurtural, UC Cooperative Extension specialist in the UC Davis Department of Viticulture and Enology; and George Zhuang, UCCE viticulture advisor in Fresno County; conduct conference panels and webinars about the process, which they say is the future of pruning for operations of 150–300 acres.

  So keep in mind as you strategize production growth and processes, “one of the greatest disadvantages to cane pruning in our future shift to mechanization is that it cannot be easily machine-pruned,” Westover said.

Questions of the Advisor

  Since Westover consults for dozens of vineyards east of the Rocky Mountains through his onsite visits and victual academy, we asked him to provide answers to the top three questions he gets regarding pruning. They are:

1.   When should I start pruning?

      A: Depending on vineyard size, time and labor, if a grower in the Northern Hemisphere uses pre-pruning or partial pruning, I encourage them to start in January and move to final pruning at a time that allows them to complete it prior to budburst. So, for example, a small grower may be able to prune in a week and can start the process 10-to-14 days before the historical average budburst date in their area. Larger vineyards obviously need more time and may be pruning steady until budburst.

2.   Do I need to protect pruning wounds from GTDs?

      A: Fungal diseases associated with GTDs are primarily spread by splashing rain. Therefore, it’s important not to prune when it’s raining or when rain is predicted within the next few days—I advise my growers to wait until after the rain. In some cases, registered fungicides can be applied to protect pruning wounds from infection, such as Topsin M—check your state registry status. If pruning wounds have healed over, or if no rain is predicted, then protective sprays can be avoided. There are also products available now that can be painted over the top of larger pruning wounds to create a physical boundary against pruning wounds, such as VitiSeal.

3.   What if I don’t finish before budburst?

      A: Ideally, all final pruning will be completed a week or so before budburst. When shoots begin to grow, they first emerge on the most distal part of a cane, which is referred to as “apical dominance” of shoots across a cane. Some growers intentionally hold off final pruning until the onset of budburst on distal bud positions, as this can delay the budburst of the lower buds retained as spurs near the cordon. This small delay in budburst can result in the avoidance of a late spring freeze by 7-to-14 days, depending on site and variety. However, if a grower doesn’t complete final pruning before the shoots on the distal nodes reach greater than two inches in length, the lower bud positions can lose fruitfulness. The bottom line: pruning needs to be completed by bud swell—and not later.

Education, Sterilization, and Clean-Up Ensures Successful Results

  Many vineyard managers hire crews with pruning experience, while some do a crash course each season with trusted volunteers. In either scenario, Westover said, you need to ensure people do what your vines require.

  “Cut-and-paste pruning strategies won’t address the needs of each block. A pruning crew is only as good as its instructor, and it’s often necessary to have a lot of supervision the first few days of pruning—and again any time the pruning strategy changes between vineyard blocks,” he said. “Educate your crew and stick with them until the end. I share videos with my clients from my website, and on a rainy day, the crew watches those. Repetition of key pruning concepts is a great way to empower your crew to make decisions on their own and quickly.”

  One example he provides is that vigorous vines with large cane diameters can retain spurs with two-count buds, whereas smaller vines or vines with some small canes may need to have several spur positions pruned back to a one-count bud. “The motto I use in my academy is ‘no wimpy wood’—which seems to resonate with growers and results in less wimpy shoots that produce inferior fruit,” Westover of Virtual Viticulture Academy told The Grapevine Magazine.

  “Weather can also cause a shift in a standard pruning protocol. For instance, in a year with high primary bud death due to freeze conditions, a grower needs to first assess the percentage of bud death in the vineyard, and then adjust the final number of count buds per vine to compensate,” he said. “This isn’t easy to do, but it can certainly help keep a vineyard in business through a tough season if done properly—and some live buds remain!”

  Myers’ pruning team includes two people on staff for a 40–plus workweek who are in the vineyard daily. One of her primary takeaway tips is proper sterilization. “Clean pruning tools at the end of each row, and especially when changing varietals.”

  Westover agreed. “This is an area of research that we have little information on at this time, but sterilizing shears after each row and—at a minimum—between blocks is a good practice. Solutions of 10% bleach or 70% isopropyl alcohol are inexpensive options to spray on shears,” he said.

  So is the work done once buds break? Not necessarily. “Stay proactive on your vineyard management programs from pruning until frost to avoid uncontrollable problems,” said Myers of Laurel Gray Vineyards. “Watch for split vines that may have happened due to extreme cold weather when the sap was rising. Remove all cut wood from the vineyard floor and spray while still dormant with lime sulfur to kill any disease spores that overwintered in mummified fruit, dead wood or old leaves.”

  Also remember that not removing enough canes “will cause over-production with a too-dense canopy, under-ripe fruit and conditions for disease,” she said. “These conditions require more labor through the growing season because the vineyard manager is constantly trying to combat these issues through summer hedging, spraying and leaf removal.”