Dr. James Osborne, Enology Extension Specialist and Associate Professor

Harvest is here and in the winery there are many things to prepare for before the fruit starts arriving. One key area to prepare for is yeast and nutrient management. While yeast and nutrient management are always key factors in conducting successful fermentations, extra care is needed in years like this where grape composition may lend itself to more problematic fermentations. Because of the warm and dry growing season fruit may contain high °Brix and low nutrients. This fruit chemistry can cause problems with alcoholic fermentations as yeast need to metabolize a greater amount of sugar with a lower amount of nutrients in a high alcohol environment. The end result is often a very slow/sluggish fermentation or fermentations that do not complete fermentation but rather stall out with a few Brix still remaining. One key factor in preventing stuck/sluggish fermentations is ensuring there is sufficient yeast nutrients present during the fermentation. Yeast assimilable nitrogen (YAN) is one of these key nutrients and insufficient amounts can result in stuck fermentations as well as increased production of hydrogen sulfide.  YAN is composed of nitrogen from ammonia (inorganic nitrogen) and nitrogen from primary amino acids (organic nitrogen). Luckily, we have a number of tools at our disposal to supplement YAN but how and when to perform this supplementation is a little more complicate.

The first step is measuring how much YAN is present in the juice/must. While you want to add enough YAN for a complete and clean fermentation, you do not want to add excessive nutrients as this can also cause problems. Large additions of YAN early in the ferment may lead to over vigorous fermentations and alter the aroma compounds produced by the yeast. In addition, residual nutrients in the wine may contribute to microbial spoilage during aging. So how much YAN do you need? Well, it depends. The general recommendation is between 150-250 mg/L for a 21-23°Brix must. If you have a higher °Brix must or are using a high nutrient demand yeast strain then you may want to consider higher YAN levels. These are not hard and fast rules but are YAN levels that have been reported by researchers and yeast manufacturers to result in fermentations with good kinetics. Aside from nitrogen, the other nutrients that are essential factors for yeast growth are the micronutrients such as the vitamins biotin, pantothenic acid, and thiamin. If you just want to increase YAN then DAP is an efficient way to do this. However, DAP does not contain any micronutrients so in addition to DAP you also should use a complex yeast nutrient that contains a blend of organic nitrogen (amino acids, peptides) and micronutrients. A balanced approach of both DAP and complex nutrients works best if you need to significantly increase your YAN levels. Nutrient additions should be carefully monitored and recorded as there are legal limits to the concentrations that can be added. For example there are limits to the amount of DAP (0.96 g/L), thiamin (0.60 mg/L), and pantothenic acid (0.048 mg/L) that can be added. For complex yeast nutrients carefully read the manufacturer’s instructions carefully to determine the max concentration of the product that can be added.

The timing of nutrient additions is important for successful fermentations. Yeast preferentially up-take ammonia (DAP) before amino acids. Therefore, one large addition of DAP at the beginning of fermentation may delay/inhibit uptake of amino acids and cause problems later in fermentation. It is therefore recommended to perform multiple additions of nutrients during the early to mid-fermentation stage. For example, add half the nutrients 12-24 hours after inoculation followed by the remainder of the nutrients around 1/3 sugar depletion. Adding nutrient supplements all at once can lead to a fast fermentation rate, and an imbalance in uptake and usage of nitrogen compounds. Alternatively, supplements added too late in the fermentation (after 2/3 fermentation) may not be utilized by the yeasts. This is because as the fermentation proceeds ethanol concentrations reach a point it impacts the yeast membrane and reduces the ability of the yeast to uptake nutrients.

Aside from YAN, the other yeast nutrient that can play a critical role in conducting successful alcoholic fermentations is oxygen. During the early stages of alcoholic fermentation Saccharomyces can use oxygen for the production of sterols. These sterols are a key component of the yeast cell membrane and will help the yeast resist osmotic stress at the beginning of fermentation and ethanol toxicity near the end of fermentation. There are two times during the fermentation where oxygen addition has been shown to be beneficial. First, once the fermentation has become active and a 1-3 0Brix drop has occurred. The second time is at about 1/3 0Brix drop. Addition of oxygen to the ferment after this time is not recommended. Pumping over or racking and returning can supply some oxygen to the ferment but using a macro-oxygenator or micro-oxygenator at a high rate is a more reliable way to provide air to the ferment.

Aside from adjusting your nutrient regime, you should also consider the yeast strains that you use for your fermentations. In warmer years with high °Brix grapes the choice of yeast strain can make a difference in the prevention of stuck fermentations. Saccharomyces cerevisiae strains vary in their ethanol tolerance as well as their preference for consuming glucose or fructose. In a typical grape juice glucose and fructose is present in an equivalent amount. However, most Saccharomyces cerevisiae yeast strains used in winemaking preferentially consume glucose so that near the end of a fermentation the majority of the remaining sugar will be fructose. This is why it is recommended that a fructophilic (fructose loving) yeast should be used to restart stuck fermentations. These yeast strains can also be used as the primary yeast for fermentation and may be a valuable tool when fermenting lots that have historically been problematic or that are high °Brix ferments. It is recommended that you talk with your yeast supplier about fructophilic yeast strains and their use.

Warmer years also typically present us with fruit containing lower acid. If acid additions are to be performed it is important to measure a few different components of acidity. The typical measurements of acidity are pH and titratable acidity (TA). The pH and TA of your juice/grapes will be impacted primarily by the concentrations of tartaric and malic acid. These acids have different strengths and so a different ratio of these acids will impact both pH and TA independently. For example, you can have two juices with very similar TAs but quite different pH values if their tartaric and malic acid concentrations differ. pH is also impacted by the buffering capacity of the juice/must. The major component of grapes that impacts buffering capacity is potassium. Grapes with high potassium concentrations can be resistant to pH change from acid additions because of this buffering capacity. For example, you may make an acid addition to a set TA level but not see the expected decrease in pH if the juice/must contains high amounts of potassium. Bench-top trials for acid adjustments are recommended so that you can an accurately determine how much acid will be needed to achieve a certain pH and what the resulting TA will be.

One additional note when it comes to calculating pre-fermentation adjustments (YAN and acid). When taking grape and juice samples for analysis, the more closely these samples represent the grape/juice in the tank the better. When assessing red grapes I would recommend taking the grape samples and crushing them by hand in a zip lock bag and letting the juice soak on the skins for a few hours (in the fridge). This will give you a more accurate pH value because the grape skins contain a significant amount of potassium that will soak out during this time. If you analyze the juice immediately after crushing the grapes then you will not account for this potassium. Grape skins also contain some amino acids and so soaking the grapes will give a better estimation of the YAN content of the grapes.

If you have additional questions please contact me at 541-737-6494 or email james.osborne@oregonstate.edu

Dr. Patty Skinkis, Viticulture Extension Specialist & Associate Professor

Excessive plant water stress can cause damage to grapevines, particularly young vines. The recent hot, dry seasons of 2014 and 2015 and the west coast drought drew awareness to water stress and its potential detrimental impacts. However, water stress can occur in any season, and an understanding of how to monitor and manage it is important to the production of healthy vineyards in any region.

This article briefly describes ways to determine whether vines are under water stress. This is the first step used in determining when to begin irrigation in response to stress. For sites that are not irrigated, the methods may be used to determine whether management tactics should be employed to conserve soil moisture or reduce soil water competition. The three most common methods to determine water stress include 1) visual symptoms, 2) leaf or stem water potential and 3) stomatal conductance.

Visual symptoms may be used to determine whether a plant is under stress. It requires training and understanding of the vine’s lifecycle, as symptoms may also be caused by other factors. When visually assessing canopies, it is important to look at shoot tips, tendrils, leaves, clusters, and overall growth. When vines are under water stress, tendrils become limp, shoot tips begin to flop downward, leaves begin to bend (petiole juncture at leaf blade begins to form a shepherds hook) and berries may begin to shrivel. Under prolonged water stress shoot tips stop growing and abscise, tendrils dry up and fall off, and basal leaves may turn yellow and abscise. It is important to consider that tendrils and shoot tips may dry up and fall off as a result of the natural cessation of growth late season, in preparation for dormancy and may not indicate water stress. Visual symptoms are important to document and are strengthened by quantitative measures. Keep in mind that water stress can lead to nutrient deficiencies  which may lead to other visual symptoms.

Leaf water potential is the most common measure conducted by commercial vineyards to determine whether vines are under water stress. A pressure chamber is used to measure the amount of pressure required to push water out of the cut end of the petiole and reflects the amount of water potential (or tension) of the water column in the leaf. It is a measure of negative pressure (- bars), although the gauge on most pressure chambers does not indicate a negative number. Typically, irrigation is initiated when leaf water potential readings reach -12 bars, which is considered moderate stress. Stem water potential, also uses a leaf to measure plant water stress, but it requires additional steps in the process, including covering a leaf with a special reflective bag for at least one hour prior to measurement. Covering the leaf limits transpiration, equalizing the water potential in the leaf close to what is experienced in the shoot (or stem). Stem water potential is usually 1-2 bars less negative as shoots are under less tension than leaves. For example, if leaf water potential readings are at -12 bars, the stem water potential on the same plant may be at -10 bars, and the leaf reading would suggest that you need to start irrigating while the stem reading does not. More information about monitoring plant water stress can be found here.


Above: The pressure chamber. The leaf is placed inside a sealed chamber and pressurized gas is added to the chamber slowly. As the pressure increases water will be forced out of the xylem and will be visible at the cut end of the stem. Note the magnifying glass for easier viewing.


Above: Stem water potential, also uses a leaf to measure plant water stress, requires additional steps in the process, including covering a leaf with a special reflective bag for at least one hour prior to measurement. Covering the leaf limits transpiration, equalizing the water potential in the leaf close to what is experienced in the shoot (or stem).


Above: When measuring water or leaf potential, make sure to cut end of the petiole for an accurate measurement.


Above: A leaf attached to a petiole is placed inside a sealed chamber and pressurised gas is added to the chamber slowly.

Some find the pressure chamber to be cumbersome due to its bulky size and have been interested in using a portable leaf porometer. A leaf porometer measures the rate of water that moves out of the stomata, known as stomatal conductance. When a vine is under water stress, stomata close and stomatal conductance of water is reduced. A vine that is not under any water stress can have stomatal conductance of >250 mmol H20/m2/s while a vine under moderate stress has <150 mmol H20/m2/s. There is a porometer on the market that is affordable for commercial vineyard use, and the cost is comparable to a pressure chamber. It may be small, but it requires training, attention to detail in collecting the data, and requires a calibration step before using the meter. This calibration needs to be done each day, before sampling begins, and again hen environmental conditions change (approximately every hour).

Both leaf water potential and stomatal conductance measures require the right equipment and training. Both tools should be used on clear, cloudless days within 1 hour before and after solar noon and not under extreme heat events, to give the most accurate readings. We have tested both pressure chambers and porometers in various trials under western Oregon conditions to monitor plant water stress (Skinkis and Schreiner Labs), and both can be good tools to determine when vines are under stress. If you are interested in those findings, contact Patty Skinkis or Paul Schreiner for more information. Whenever using quantitative measure of plant water stress, it is important to make note of visual symptoms, as they may help interpret conditions of the vines.

NOTE:  The reference to porometers and pressure chambers are for local companies that have developed these devices. There may be other companies that provide similar products, and the mention of these two companies does not imply recommendation or endorsement of those products over any other similar product.

Additional Reading

The Pressure Chamber (The Bomb) – UC Davis Fruit & Nut Research Information

Measuring Water Status Using a Pressure Chamber – eXtension.org

Grapevine Management under Drought Conditions

Irrigation Basics for Eastern Washington Vineyards

Dr. Patty Skinkis, Viticulture Extension Specialist & Associate Professor

There has been an increase in the number of reported cases of stunted vine growth and potential trunk disease this spring in the Willamette Valley. The symptoms ranged from delayed bud break to lagging shoot growth compared to healthy blocks, and in some cases led to shoots with distorted and almost tattered-looking leaves. The symptoms looked different than the typical culprits of herbicide drift, frost damage, rust/bud mite feeding, or micronutrient deficiency. Upon closer inspection by sawing into cordons and trunks, significant cankers (dead areas within the vine trunk) were found, and this suggested the potential cause of the limited shoot growth. Although visual symptoms suggested trunk disease, samples were submitted to OSU Plant Clinic to confirm which disease organisms may be causing the damage.

Knowing what trunk disease organisms are present is helpful in understanding next steps for managing the disease. Dr. Melodie Putnam, OSU Plant Clinic Director, summarized the importance of identifying the disease-causing organisms and provides visual examples of trunk disease symptoms in a seminar archived online here. Trunk disease has become more of a “hot topic” in recent years both nationally and internationally. In 2015, Dr. Jose Urbez Torres visited OSU and growers in the north Willamette Valley and southern Oregon to share his expertise and research about trunk diseases in California and British Columbia. His archived seminar is available online here. Research on trunk diseases of grapevines is currently being led by Dr. Kendra Baumgartner, a USDA-ARS plant pathologist from Davis, CA. The work is funded by a federal grant and is aimed at understanding both basic and applied aspects of managing trunk diseases in grapevines and other tree fruit and nut crops. You can learn more about the research here.

Grapevine trunk diseases don’t lead to immediate vine decline. The vine symptoms that are being expressed this spring are likely due to infection years ago, and the vineyards are just now showing the symptoms due to some prior vine stress. The two record breaking yield and heat/drought vintages of 2014 and 2015 may have led to more nutrient and/or water stress that could lead to poor nutrient or carbohydrate storages for early spring growth. The research team on the federal trunk disease grant are working to understand how water stress impacts the disease.

Please see the links below for more information.

The Oregon Wine Research Institute is pleased to announce that Alexander Levin will be joining the OSU Department of Horticulture as Assistant Professor of Viticulture in early fall, 2016. He will be based at the Southern Oregon Research and Extension Center in Central Point.

Dr. Levin completed his Ph.D. degree in horticulture and agronomy at UC Davis under Drs. Mark Matthews and Larry Williams. Prior to pursuing a Ph.D., Alexander completed a bachelor’s degree in psychology at University of Michigan. He gained hands-on experience
in the wine industry while working in Napa Valley, CA as a harvest intern, and at Beringer Vineyards in St. Helena, CA. His primary research interests include investigating genetic differences on drought response between cultivars, evaluating plant water status, leaf conductance and vegetative growth, and the development of deficit irrigation regimes to optimize production goals. He conducted a multi-year field study investigating vine performance of 17 red winegrape cultivars under deficit irrigation.

Alexander’s future research and Extension plans include working with grape growers to identify appropriate management practices, developing suitable irrigation practices for the region, and utilizing field data to optimize grape and wine quality. He also looks forward to collaborating with other researchers, Extension specialists, grape growers, and stakeholders to further develop the Southern Oregon grape and wine industry using effective
management practices.

For more information, please contact: Richard Roseberg, Director- Southern Oregon
Research & Ext. Center. Phone: 541-772-5165, email: richard.roseberg@oregonstate.edu.


Dr. Patty Skinkis, Viticulture Extension Specialist & Associate Professor, OSU

Canopy management, including hedging, leaf and lateral removal, is of paramount importance at this time of year. These practices can change canopy microclimate and thereby influence how fruit develops and how well your fungicides are deposited to control powdery mildew and Botrytis bunch rot. It is important to consider how and when to apply these practices. If canopy management tasks are not done at the correct time, there may be issues that arise. Below are some important considerations with regard to leaf removal, one of the more queried practices in canopy management.

Leaf removal in the cluster zone is an important practice for vineyards with moderate to high vine vigor. Leaves should be removed between fruit set and bunch closure. I often receive reports of berry sunburn due to leaf removal, and in many cases, this was the result of leaf removal at or just prior to véraison. The cluster is relatively resistant to sun exposure in earlier stages of development from bloom to bunch closure. However, once berries begin to ripen (near véraison), the cells of the berry skin become less able to withstand high sun and heat exposure. Studies show that clusters with earlier exposure have more phenolics that likely help prevent damage from exposure.

No pull and 100 percent leaf pull Sept AS 2010
Results of no leaf removal (left) and 100% cluster zone leaf removal (right) in a trial conducted in a commercial Pinot noir vineyard in the Dundee Hills AVA during 2010. Leaves were removed well before bunch closure, and the photo was taken in early September that year. Poor fruit set that is visible in the 100% leaf removal due to the year, not the treatments.

How much leaf area should be removed? There have been numerous leaf removal studies conducted in Oregon and elsewhere. The industry standard of removing leaves from the cluster zone on only the morning-sun side of the canopy (east side of N-S rows) has been shown to be effective from the standpoint of aroma and color development in Pinot noir. You can read more about this in a recent article by OSU researchers. This research compared no leaf removal to 50% and 100% of leaves removed in the cluster zone and the industry standard of east-side leaf removal. Leaf removal enhanced color and aromas more than no leaf removal (Feng et al. 2015). Several other studies have also been conducted in Pinot noir with 100% leaf removal in the cluster zone where leaves were removed on both sides of the canopy from 2008 to 2015. These studies showed increases in Pinot noir anthocyanin (color) compared to no leaf removal without any issues with sunburn (Lee and Skinkis 2013). Despite complete exposure from shortly after fruit set, there was no excessive sunburn, even in hot seasons like 2014 and 2015 (Reeve & Skinkis, in preparation). Research conducted in eastern Washington’s hot, arid climate with 100% leaf removal of white grape cultivars showed enhanced late season spray coverage and no difference in sunburn compared to no leaf removal (Komm and Moyer 2015). It is important to note that some berry burn may occur due to other factors and not simply from leaf removal itself, including use of certain adjuvants or applying sprays at a certain time relative to the heat of the day.

Although leaf removal is a common and popular practice in western Oregon, it is not necessary in all vineyards and may not result in the same outcomes. Vines that are of low vigor have more well-exposed clusters than high vigor vines, and they may not require additional exposure. Also, leaf removal in low vigor vines may lead to insufficient canopy leaf area for vine productivity and fruit ripening. Furthermore, vines that are under water stress may experience different levels of sunburn/heat stress to the berries with leaf removal, and care should be taken to ensure sufficient coordinated management of irrigation and canopy management.

Additional Reading

Feng, H., F. Yuan, P.A. Skinkis and M.C. Qian. 2015. Influence of cluster zone leaf removal on Pinot noir grape chemical and volatile composition. Food Chemistry. 173: 414-423. http://www.sciencedirect.com/science/article/pii/S0308814614015374. Published with permission in Practical Winery & Vineyard Magazine in June 2016: http://files.ctctcdn.com/27fc1a43201/85469b81-aef1-46a9-aa2a-b256e7f2a34b.pdf

Komm, B.L. and M.M. Moyer. 2015. Effect of early fruit-zone leaf removal on canopy development and fruit quality in Riesling and Sauvignon Blanc. American Journal of Enology and Viticulture 66: 424–34. http://www.ajevonline.org/content/66/4/424

Lee, J. and P.A. Skinkis. 2013. Oregon ‘Pinot noir’ grape anthocyanin enhancement by early leaf removal. Food Chemistry. 139:893-901. http://ir.library.oregonstate.edu/xmlui/handle/1957/39412

Skinkis, P.A. and A.J. Vance. 2013. Understanding Vine Balance: An important concept in vineyard management. Oregon State University Extension Service. EM 9068. https://catalog.extension.oregonstate.edu/em9068

Vance, A.J., A.L. Reeve, and P. A. Skinkis. 2013. The Role of Canopy Management in Vine Balance. Oregon State University Extension Service. EM 9071. https://catalog.extension.oregonstate.edu/em9071

The OWRI is excited to announce our first annual Sparkling Wine Symposium on Thursday, April 14. This all day symposium is led by experts from Oregon, California and Champagne, France, and designed for wine industry members seeking a comprehensive understanding of sparkling wine.

This workshop will cover the theories and economics behind sparking wine production and guide participants through two wine tastings. By working through several sparkling examples, participants will review the climate, soils, sub-regions and winemaking process of sparkling wine in an interactive format. Come prepared to sip, savor and discuss the factors that make sparkling wine unique and distinctive.
For more information, visit this link: http://blogs.oregonstate.edu/champagneworkshop/
Do We Need to Sterilize Pruners?  
Jay W. Pscheidt, Ph.D.                                                                     

Professor of Botany and Plant Pathology and Extension Plant Pathology Specialist, Oregon State University                

In late May 2015, José Úrbez-Torres, Research Plant Pathologist, Pacific Agri-Food Research Centre, Summerland, Canada visited Oregon. Dr. Úrbez-Torres’ research focuses on identifying and managing grapevine trunk diseases. Trunk pathogens infect grapevines through injuries and wounds; even those made annually during dormant season pruning,. Prevention is the key to manage these diseases. Many growers came away from his seminar believing that sanitation of pruners was required.
Dr. Úrbez-Torres explained that it was a misunderstanding and that he was not recommending or promoting this practice. He did outline some recent research from Spain (Agustí-Brisach et al 2015) that showed that many of these trunk pathogens could be detected on pruning shears and could be transmitted to healthy vines through pruning, but the devil is in the details. The research group used a very sensitive technique (nested PCR) to find specific pathogens on the pruning shears. The technique can detect extremely small amounts of DNA that may represent a few pathogen propagules (such as live or dead fungal spores or mycelia). So, yes, the pathogens (alive or dead) can be found on shears after pruning an infected vineyard, but in very small numbers.
The research group in Spain also placed a huge amount of spores or mycelial fragments (ten thousand to a million) on pruning shears to see if just cutting a healthy vine with contaminated shears could transmit them to the wound. So, yes, at these high levels, pruning shears can transmit these trunk pathogens (with a frequency below 50% at the highest inoculum level). These inoculum levels, however, are far above would be found in a normal, practical situation. Given this information, Dr. Úrbez-Torres says the risk of transmission via pruning shears is “insignificant.”
I know there are those of you who are risk-adverse and will want to clean your pruning shears. If you choose to do this, here are some practical suggestions that will make this task both effective and efficient. First, you must start with clean and sharp shears. Cuts made with sharp shears heal much more quickly. Sharpen shears at every worker rest break. Most crews already bring sharpening tools since it is so much less tiring pruning all day with a sharp shears.
Disinfesting shears can be done with a wide variety of solutions but the key is starting with a clean pruning shear and using long contact times. Think soaking rather than dipping. I recommend you carry at least two sets of shears, one to soak and one to use while the other soaks. When you need to change the shears after every (insert your own tolerance statement) vine, row, section, vineyard, etc. place the used shear to soak in the disinfestant and pick up the one that has been soaking and continue pruning.
Although the bleach solution (10% Clorox – 1 part bleach to 9 parts water) that Dr. Torres mentioned is very quick and effective to oxidize pathogen propagules, it also oxidizes your shears – they rust! You can use other solutions as long as you soak for the duration mentioned above. This includes various alcohols (70% ethanol or isopropanol-rubbing alcohol), peroxides (OxiDate or ZeroTol), or quaternary ammonia (KleenGrow or Physan 20). Many of these products have labels to follow but other general cleaning solutions may also be useful. Change the solution frequently – each break, day, etc.
Managing grapevine trunk diseases will require more tactics such as a wound protectant after pruning. These tactics can be found at:
Bottom Line: No, you don’t need to sterilize or disinfest your pruning shears.
Reference: Agustí-Brisach, C., León, M., Garcia-Jimenez, J. and Armengol, J. 2015. Detection of Grapevine Fungal Trunk Pathogens on Pruning Shears and Evaluation of Their Potential for Spread of Infection. Plant Disease 99:976-981.

The sky is falling!

(Well, maybe not.)

Jay W. Pscheidt, Ph.D.
Professor of Botany and Plant Pathology and Extension Plant Pathology Specialist, Oregon State University

The new Compendium of Grape Diseases, Disorders and Pests (Wilcox et al 2015) points out the multitude of problems that can beset grapes. Oregon’s grape industry has done well to avoid many of these troubles using geographic isolation, unique climate conditions and planting stock quarantines. Grapes are still susceptible to all these problems, which could arrive and cause havoc on any growing season. When one of these problems does come along, we may sound a lot like “Chicken Little” declaring that the sky is falling. Several disease issues have fallen onto our doorstep that need to be discussed. Although some are very serious and not unexpected, all can be dealt with. These issues include Xylella, sterilizing pruners, fungicide resistance and climate change, which we will address throughout the season.


In October, 2015, the presence of the bacterium Xylella fastidiosa was confirmed by the Oregon Department of Agriculture (ODA) in several pear trees growing in the field germplasm collection at the USDA Repository in Corvallis. Grape growers may be alarmed knowing that Pierce’s Disease is caused by Xylella fastidiosa subsp. fastidiosa. Pierce’s Disease has been a high-profile and rapidly increasing disease in California and other southern states but has not been known to be in the Pacific Northwest. At this time, the preliminary DNA sequence data suggests the bacterium on pear is X. fastidiosa subsp. multiplex, which can cause a chronic leaf-scorching disease in many different species of woody landscape shrubs and shade trees, including oak, elm, and other trees – but not grape. (Whooh!)

There are still a ton of questions that need to be answered in the coming months and years about this find. Keep half an ear open on this problem.

Why don’t find Pierce’s Disease in the Pacific Northwest? Our climate may be too cold for the pathogen to survive. Infected grapevines do not retain the pathogen after a cold dormant season typical of continental climates. Also the majority of leaf hoppers (xylem feeding insects that vector the bacterium) found in PNW surveys are Western grape leafhopper which are not efficient vectors of Xylella. The Blue-green sharpshooter will vector Xylella and has been found in the Willamette Valley, Columbia Gorge, Medford and Milton-Freewater areas of Oregon. This leafhopper is usually found in surrounding vegetation but less in vineyards. The glassy winged sharpshooter, a very efficient vector, has not been found in or around Oregon vineyards nor is it abundant in the PNW.

If you are still worried, you can keep an eye out for various symptoms. Pierce’s Disease first appears as water stress in midsummer and gradually gets worse. Leaves become slightly yellow or red along margins in white and red varieties, respectively, and eventually leaf margins dry or die in concentric zones. Fruit clusters shrivel or raisin. Dried leaves fall, leaving the petiole attached to the cane. Wood on new canes matures irregularly, producing patches of green, surrounded by mature brown bark. ‘Pinot Noir’ and ‘Cabernet Sauvignon’ have highly regular zones of progressive marginal discoloration and drying on blades. Unfortunately, any other problem that blocks, inhibits or limits water from getting to the leaves will produce similar symptoms. Fungal cankers, damaged trunks, girdling roots, gopher damage, herbicide injury and root rots also can produce similar symptoms.

Bottom Line: Finding Xylella on pears in Oregon is not, at this time, a worry for grape growers.

Reference: Wilcox, W. F., Gubler, W. D. and Uyemoto, J. K. 2015. Compendium of grape diseases, disorders, and pests. Second edition. St. Paul, MN: APS Press.

Clive Kaiser, Extension Tree Fruit Specialist
Oregon State University, Umatilla County

On July 21, 2015, a dedicated group of growers from Oregon and Washington gathered in the Walla Walla Valley to listen to renowned experts about how to minimize cold damage to grapevines and fruit trees.

Dr. Glenn McGourty, viticulture and plant science advisor, University of California Cooperative Extension in Mendocino and Lake counties, outlined the basics of frost protection, offering practical examples of passive and active frost protection techniques and the role of ice nucleating bacteria and how to control them. He also discussed remediation of frost-damaged vines and differentiated between winter injury, when temperatures drop below -12°F and frost events when temperatures drop below 32°F.  During the latter, ice crystals form between the cells and disrupt the cell membranes. With cell membrane integrity gone, the cell contents desiccate and the cells fail. The foliage turns black in spring and brown in fall. Glenn also distinguished between radiation frosts- when inversions occur- versus advective frosts, when a large, cold air mass is usually accompanied by wind and low humidity.

Measures to avoid frost exposure include:

  1. Careful site selection; uplands are best if you have the choice. Glenn cited the age old Latin saying “Bacchus amat colle” which translates to “Bacchus loves the hillock” and further suggested south and west facing slopes tend to be the warmest – one upside to other aspects is that bud break may be delayed in spring, thus helping to avoid early spring frosts.
  2. Manage brush, trees and other air dams that trap cold air in the vineyard.
  3. Soil water management: bare, packed soils offer the most protection but present risk of erosion, loss of soil organic matter, destruction of soil structure, and poor footing for early spring spraying.
  4. Maintain the soil moisture near field capacity: wet the top 12 inches of the soil surface 2-3 days in advance of a predicted frost event. It is not necessary to wet the entire profile as the top layer provides insulation and protects soil lower in the profile from losing heat. Glenn also compared different types of vineyard floor management systems ranging from bare, firm, moist ground (being the warmest) to tall cover crops with restricted air drainage, which can be6-8°F cooler.
  5. Delay pruning where practical: consider double pruning by leaving long spurs (6-10 buds), which can be cut back to two spurs later in spring. This will result in delayed bud break and can avoid frost damage by gaining a week of delay.
  6. Mow cover crop as close to the ground as possible in late winter before bud break and the first spring frost.
  7. If available, utilize overhead sprinklers as frost protection, especially where cover crops are present.

Glenn discussed ice nucleating bacteria, which are ubiquitous in nature. Common examples include Pseudomonas syringae, Pseudomonas flourescens, Psuedomonas viridflava, Erwinia herbicola and Xanthamonas campestris var. vesicatoria. The presence of these bacteria will lead to increased freezing. For example, snow-blowing freeze-dried Pseudomonas syringae, which will produce snow at 27°F versus water at 15°F, is an obvious effect of these pathogens, therefore controlling the bacteria will help prevent ice nucleation. Applying up to three copper hydroxide sprays one week apart in spring, after bud break but before a frost event, will have a beneficial effect of protecting foliage against frost damage as long as temperatures do not drop below 25°F.

Glenn also discussed his regeneration pruning work on damaged vines. This research indicated that comparing no pruning to breaking damaged shoots, cutting out spurs, or cutting damaged shoots, yields mixed results and is cultivar dependent. Positive impacts of pruning were seen in Chardonnay but not Cabernet Sauvignon. Pruning did not impact fruit quality on either cultivar, however, significant differences occurred in shoot emergence of spurs which may result in lower pruning costs in future years.

Dr. Imed Dami, research and extension viticulturist at Ohio State University discussed his research using vegetable oil to delay bud break.  He discovered that an application of eight percent vegetable oil (v/v) with an emulsifier applied mid-winter can delay bud break by seven to ten days without affecting yield or fruit quality.  He also discussed other practices such as “hilling up” (burying graft unions with soil) the vines to protect the stems against cold damage. When temperatures dropped below 15°F in Ohio, the best pruning technique as found to be give-bud hedging. When regrowth from the ground took place, training and pulling the new shoots immediately resulted in the best recovery over time. Bull canes (vigorous canes greater than pencil thickness) must be removed since they often do not harden off properly resulting in more cold damage the next winter.

Dr. Mark Battany, University of California Cooperative Extension farm advisory in San Luis Obispo County and a self-confessed gizmologist, presented his findings on active versus passive control of frost. He highlighted the importance of managing cover crops and delaying bud break in spring, as well as the importance of knowing the temperature at both five and 35 feet above ground level. Wind machines only work when an inversion exists due to radiant conditions. In fact, when an advective freeze (polar express) occurs you can cause more damage by running a wind machine, as the air temperature at 35 feet can be substantially colder than at five feet. He also explained that for a wind machine to work well the temperature difference between the two different heights needs to be at least 8°F for the wind machine to have an effect. Mixing the air from the warmer layer will result in averaging of the two temperatures and a 4°F gain temperatures can be expected.  He also presented work showing that wind machines which blow warm air down are far more effective that those that blow cold air up.  He suggested using black float ball modified sensors rather than standard shielded air temperature readings as the latter are not accurate measures of plant tissue temperatures at night because objects exposed to the sky are subject to radiation heat losses. Consequently, the leaf temperatures are actually colder that those in the standard shielded sensors.

Finally, Dr. Kevin Kerr of Brock University provided an overview of the cold management techniques utilized around the Niagara peninsula in Canada. The focus of Kevin’s work is to understand and predict when freezing temperatures are going cause issues. His team has developed an extensive network of differential thermal analysis (DTA) using programmable freezers and measure cold hardiness of buds throughout the region. This is presented to participants through a novel VineAlert system. This includes both rates of acclimation and de-acclimation of bud. This information is being used by the growers to determine precisely when the wind machines will be required to help protect buds and as a result has saved their industry more than $13.8 million in lost grape revenue as well as saving another $1 million in operating costs of the wind machines. Lessons learned include: – early shutting down of vines in fall result in hardier buds; a wet harvest season results in slower vine acclimation; excessive crop load result in less hardy vines; too little crop leads to excess vigor which results in less hardy vines; de-acclimation begins in late January with a very rapid rate of de-acclimation during March; once the vine de-acclimates, there is no going back to maximum hardiness vines need 72 hours of sub-32°F re-exposure to stop de-acclimation from continuing.; maximum hardiness is achieved by prolonged exposure at 32°F or colder but does NOT require extremely cold temperatures (<20°F) to reach maximum cold hardiness.

All in all, the volume of information imparted by the speakers was vast. Both theoretical knowledge and practical applications were abundant and useful to all the participants, who expressed their sincere thanks to all the speakers for making the trek to the Walla Walla Valley.

If you have any additional questions about this workshop, please contact me at: clive.kaiser@oregonstate.edu.