By Bryan Hed
Since the new year was ushered in we have had several scary moments when Mother Nature unleashed an “excess of personality.” I’m referring to the cold weather events we experienced around January 1, 7, and 14, when temperatures slipped down below zero in many places across Pennsylvania, even in some south central parts of the state. As many of you might remember, the last time we saw below zero temperatures that far south (February from hell, 2015) primary bud damage was widespread and grapevine trunks in vineyards all over Pennsylvania (and certainly other parts of the Northeast) exploded in crown gall the following spring. This generated a two-year trunk renewal process that we’ve only just recovered from. Therefore, this may be a good time to review grapevine winter hardiness and the factors that affect it, as well as how we can prepare for possible remediation pruning and renewal this spring.
Now I don’t want to raise alarm bells just yet, as the conditions we’ve experienced this January haven’t been as horrific as February of 2015. But it’s always good to be prepared for any potential consequences, like bud loss and trunk damage, so we can anticipate altering our winter pruning plans and production practices this season.
Let’s start with a review of the temperature stats available to everyone on the NEWA website (newa.cornell.edu) and see just how cold it got in various places across the state during the first half of January. In the table below, I’ve listed low temperatures for January 1, 7, and 14 for many of the NEWA locations. Starting at northeastern PA and moving counterclockwise to swing back up into northern New Jersey and finally western New York, we get the following data (Table 1).
Areas of southeastern and northwestern Pennsylvania, at opposite corners of the state, appear to have escaped the below-zero temperatures for the most part, but some areas of south central Pennsylvania took a hit (look at York Springs). Areas of southwestern Pennsylvania experienced some of the most extended periods of below-zero weather, and parts of northeastern and central Pennsylvania also got quite cold. The temperature low is the most important bit to consider when sizing up vine bud damage, but the duration of those lows can affect the extent of trunk damage, especially in big old trunks where it may take longer for the core to reach ambient temperatures. Up in the northwestern corner of the state, the buffering effect of Lake Erie probably played a role in our relatively mild temperatures during that period, and we expect little to no damage to most of our vines as our wine industry there is heavily invested in tougher hybrids. The Erie area was also blessed (?) with a heap of snow (10 feet!) before the cold snap that provided added protection to bud unions of grafted vines.
If you’re anticipating primary bud damage, here’s a review of the ranges of temperatures for the LT50 (low temperature at which 50% of primary buds fail to survive) for the cultivars you’re growing. For Vitis vinifera, the LT50 range of the most winter sensitive cultivars falls between 5o and -5oF. This includes cultivars like Merlot and Syrah. But for most cultivars of V. vinifera, LT50 values fall more in the 0o to -8oF range (Chardonnay, Cabernet Sauvignon, Pinot gris, Pinot noir, Gewurztraminer). And finally, there’s the tougher V. vinifera and sensitive hybrids that have buds with LT50 values of -5o to -10oF. This includes cultivars like Riesling, Cabernet franc, Lemberger, and Chambourcin. On the flip side, most hybrids fall into the -10o to -15oF range (which is why Northeastern U.S. vineyards are perhaps still more invested in hybrids than V. vinifera). Then there are the V. labrusca (Concord) and the Minnesota hybrids that range from -15o down to -30oF for cultivars like Frontenac and LaCrescent. Unfortunately, we don’t have such helpful ranges for determining trunk damage, which often comes with more profound consequences and is costlier to address.
Rapid temperature drops are often the most devastating in terms of the extent of damage. Fortunately, December temperatures this winter descended very gradually giving vines time to fully acclimate to cold weather extremes. In fact, recent data from the Cornell research group in the Finger Lakes region of New York shows that LT50 values for primary buds of several cultivars were close to, or at, maximum hardiness. Therefore, it is hoped that many Northeastern U.S. vineyards were well prepped and close to their hardiest when these cold events occurred. On the other hand, any given cultivar in central New York is likely to be a bit more cold hardy than that same cultivar growing in southern Pennsylvania, simply because vines farther north will have accumulated more cooling units than those farther south. So there is the possibility of bud and—worse yet—trunk damage in parts of PA, to the more sensitive cultivars of V. vinifera.
We also had a balmy warm period during the second week in January that pumped temperatures up into the 60s in some places before plunging back down into single digits. However, it’s unlikely the brief warm period was long enough to cause any deacclimation of vines before cold temperatures resumed, and little, if any harm, is expected from that event.
The capacity for cold hardiness is mostly determined by genetics. As I alluded to above, V. vinifera cultivars are generally the most sensitive to cold winter temperature extremes, French hybrids are generally hardier, and native V. labrusca cultivars are often the toughest. Nevertheless, other site specific factors can come into play to affect cold hardiness, and this is often the reason for the range in the LT50 values. For example, there’s vine health to consider; vines that finished the season with relatively disease-free canopies and balanced crop levels can be expected to be hardier (within their genetic range) than vines that were over-cropped and/or heavily diseased. At times like these, we can’t emphasize enough how important it is to maintain your vines and production strategy with a view to optimizing their chances of surviving every winter. Other stresses like drought or flooded soils (during the growing season) that we can’t do much to control, and infection by leafroll viruses, can also play a significant role in reducing vine cold hardiness.
If you suspect damage, you should delay winter pruning of your vines, according to Dr. Michela Centinari. Feel free to revisit her previous blog posts and others at psuwineandgrapes.wordpress.com. Type “cold hardiness” or “winter injury” into the search box, and you’ll quickly and easily gain access to several timely blogs.
Bud damage can be estimated from 100 nodes collected from each potentially compromised vineyard block. Typically, gather ten, 10-node canes from each area, but do not sample from blocks randomly, unless the block is relatively uniform. If a block is made up of pronounced low and high areas (or some other site feature that would affect vine health and bud survival) make sure you sample from those areas separately as they will likely have experienced different temperature lows (Zabadal et al. 2007). You may find that vines in high areas need no or less special pruning consideration than vines in low areas that suffered more primary bud damage and will require increased remediation.
Once you have your sample, bring the canes inside to warm up a bit and make cuts (with a razor blade) through the cross section of the bud to reveal the health (bright green) or death (brown) of primary, secondary, and tertiary buds. You’ll need a magnifying glass to make this determination as you examine each bud. You should figure that primaries will contribute two thirds of your crop and secondaries, one third when considering how many “extra” buds to leave during pruning. And remember that some bud damage, up to 15% or so, is normal. If you’ve lost a third of your primaries, leave a third more nodes as you do your dormant pruning. If you’ve lost half your primaries, double the nodes you leave, and so on. However, when bud mortality is very high (more than half the primary buds are dead), it may not be cost effective to do any dormant pruning as it is likely there are more sinister consequences afoot, like severe trunk damage that is much harder to quantify. A “wait and see” strategy, or at least very minimal pruning, may be best for severely injured vines (Figure 1) and trunk damage will manifest itself in spring by generating excessive sucker growth (Figure 2). And one more thing: Secondary buds are often more hardy than primaries, may have survived to a larger extent, and in some cultivars, can be incredibly fruitful. This is especially true of some hybrid varieties like DeChaunac. So, to make more informed decisions when winter damage is suspected, you have to know the fruitful potential of your cultivar; and in cases where primary bud mortality is high, it’s therefore important to also assess the mortality of secondary buds.
Another great fear is the appearance of crown gall, mainly at the base of trunks. This disease is caused by a bacterium that lives in the vine. However, the bacterium generally doesn’t cause gall formation on trunks until some injury occurs, usually from severe winter cold damage near the soil line or just above grafts on grafted vines (if you hilled over the grafts last fall). Another search at psuwineandgrapes.wordpress.com will bring up information on how to deal with this disease. You can also visit What we have learned about crown gall for an update on research into this disease from Dr. Tom Burr and his research group at Cornell University. Tom has devoted a lifetime to researching grape crown gall and many advances have been made over the years. But it’s still a huge problem for Northeastern U.S. grape growers; and crown gall problems will likely increase as our industry becomes more and more heavily invested in the most susceptible cultivars of V. vinifera.
With more sensitive detection methods, Tom’s group is getting us closer and closer to crown gall-free mother vines and planting stock, but they’re also discovering that the crown gall bacterium is everywhere grapevines are located. Not restricted to internal grapevine tissues; it’s also found on external surfaces of cultivated and wild grapevines. So, clean planting stock may still acquire the pathogen internally down the road and management of crown gall, once vines are infected, will continue to be an important part of life in any vineyard that experiences cold winter temperature extremes. However, there is potential for a commercial product that inhibits gall formation, which can be applied to infected vines. The product is actually a non-gall-forming, non-root-necrotizing version of the crown gall bacterium that is applied to grape wounds and inhibits the gall-forming characteristic of the pathogenic strains of the bacterium. This product is still under development in lab and greenhouse tests, awaiting field nursery trials soon.
If you do happen to meet up with some crown gall development this spring, galled trunks can be nursed through the 2018 season to produce at least a partial crop while you train up suckers (from below the galls) as renewal trunks. When our Chancellor vineyard was struck with widespread crown gall in the 2015 season, we were able to harvest a couple of decent sized crops while trunk renewal was taking place (Figure 2), and we never went a single season without some crop. There’s also the issue of crop insurance to think of; adjusters may want you to leave damaged trunks in place so they can more accurately document the economic damage from winter cold.
Lastly, a great guide to grapevine winter cold damage was published about 10 years ago by several experts. In fact, information from that guide was used in composing large parts of this blog and I highly recommend you read it. It’s an excellent publication, the result of many years of outstanding research by a number of leading scientists and extension specialists from all over the Northeastern U.S. The details of that publication are found below and you can purchase a hard copy for 15 bucksby clicking here: Winter Injury to Grapevines and Methods of Protection (E2930).
For those of you who can spend hours reading off of a computer screen without going blind, you can also access a web version of the document at msue.anr.msu.edu/uploads/files/e2930.pdf.
Zabadal, TJ, Dami, IE, Goiffinet, MC, Martinson, TE, and Chien, ML. 2007. Winter injury to grapevines and methods of protection. Extension Bulletin E2930. Michigan University Extension
By: Michela Centinari and Bryan Hed
As harvest ends it is a good practice to review the season carefully, before getting busy with winter pruning and preparation for the next growing season. In the fall issue of Grape Press, the quarterly newsletter of the Virginia Vineyards Association edited by Bob and Chris Garsson, you can find some good examples of regional reports of the growing season written by wine grape growers across Virginia. It is interesting and informative to read growers stories and learn what they experienced in the vineyard and their perception of the current vintage. In addition, Drs. Tony Wolf and Mizuho Nita (Viticulture and Grape Pathology Extension Specialists, respectively, at Virginia Tech University) contributed to the quarterly publication. The final seasonal issue of Veraison to Harvest, electronic newsletter of the Cornell viticulture and enology Extension personnel, also provided a comprehensive overview of the grape and wine season in New York state, which was written by Chris Gerling .
With this short article we will provide a succinct overview of the season in Pennsylvania (PA) and we will share some of the data collected during the season for the research project NE-1020 “multi-state evaluation of wine grape cultivars and clones.” Our observations are based on the data we collected and on feedback we received from some of the PA wine grape growers throughout the state. We welcome more PA wine grape growers to share their stories with us by adding a “comment” on this blog post.
Let’s start once again with the winter:
It was a cold winter in many regions of Pennsylvania, but in the Lake Erie region, it was extremely cold. At the Penn State Lake Erie Regional Grape Research and Extension Center (LERGREC) temperatures bottomed out at about -21 °F (-30 °C) on February 16, 2015. Unfortunately more cold events (-13, -14 and -15°F) were recorded over the following ten days. As expected, extensive freeze injury was observed in the Erie region not only on Vitis vinifera cultivars, but also on inter-specific hybrids and native wine grape cultivars. Among the inter-specific hybrids Traminette, Cayuga White, Vidal and Valvin Muscat were some of cultivars that experienced extensive damage as reported by growers. Even Concord and Niagara sustained bud and trunk injuries . Luke Haggerty and Kevin Martin reported that many Concord growers retained more buds than they typically do to compensate for observed winter bud injury. Large berries and more buds helped Concord growers to maintain crop levels near average .
After budbreak bud mortality data were collected on 10 hybrid cultivars established in the cultivar evaluation vineyard at the LERGREC (Figure 1). The vines were planted in 2008 as part of the NE-1020 project. Bud mortality was not evaluated in the V. vinifera cultivars due to the extensive level of winter injury (e.g., 100% bud mortality, and trunk injury in some of the cultivars). On a positive note, only 20% or lower bud mortality was recorded in Marquette, La Crescent, and MN1235, cold-hardy cultivars developed by the breeding program of the University of Minnesota (Figure 1). However, other hybrid cultivars, such as Vidal, Chambourcin, and NY 81.0315.17 (Cayuga White X Riesling) sustained 60% or higher bud mortality. Trunk injury was observed mostly in Noiret, NY81.0315.17 and Traminette. Fifty, 17, and 8% of the Noiret, NY81.0315.17 and Traminette vines, respectively, collapsed during the summer.
The last two winters are a reminder of the importance of cultivar and site selection, and how crop diversification can help growers to maintain sustainable yields in cold climate regions.
The yield data collected at harvest from the cultivar evaluation trial established at LERGREC are shown in Figure 2. For the second consecutive year no crop was harvested from the V. vinifera cultivars. Within the hybrid cultivars, crop level varied from 1.8 tons/acre in Norton to 5.3 tons/acre in Chambourcin. The only cultivar that needed crop adjustment was Chancellor. The lower than average yield recorded in Marquette was attributed mostly to high levels of bird damage to the fruit. Due to its early fruit ripening, earlier than the nearby Concord that seems to work greatly as bird repellent, Marquette seems to be the preferred bird target.
Overall, we did not receive many inquiries from growers in the other regions of the state concerning cold injury as we did last season. Although it was a cold winter, fewer temperature fluctuations were recorded in 2014-2015 as compared to the previous winter (2013-2014). The long stretch of cold temperatures may have provided a positive, reinforcing maintenance of the vines’ mid-winter cold hardiness. Freeze damage was observed in Northeastern Pennsylvania in some of the V. vinifera cultivars, such as Pinot Grigio and Dornfelder. Growers attributed part of the damage (i.e., crown gall) to the previous winter (2013-2014) low temperatures. No above-average winter damage was observed in the southern part of the state.
Please note that these are general observations. The level of winter injury varies greatly with genotype, along with other factors. So these observations may not match what you experienced if, for instance, you grow tender V. vinifera cultivars (i.e., Tannat, Malbec, Syrah, etc.) in a cool/cold climate region. For example, we harvested only 0.4 tons/ acre of Tannat and Malbec grapes at the Penn State Fruit Research and Extension Center in Biglerville (South Central PA). Those extremely low crop levels were due to bud and trunk injuries sustained by those cultivars in the last two winters.
The vast range of varietal winter hardiness expressed in the NE-1020 vineyards over the past two brutal winters has left us with many good lessons for grape growing in the Northeastern U.S., and will serve as a rich source of science based information toward more sustainable grape production in PA.
Weather during the growing season:
In Figures 3 and 4 we reported the cumulative precipitation and growing degree days (GDDs) recorded at the two Penn State research stations located in the South Central (Biglerville) and Northwest (North East) part of the state. We also included the 2013 and 2014 data, so you can compare this season’s heat accumulation (GDD) and precipitation’s pattern and amount with those of the two previous seasons.
Precipitation: June will be definitely remembered as the wettest month of the season in 2015 (Figure 3). For instance, in Biglerville (South Central, PA) around 10 inches of rain were recorded in June. High precipitation level during bloom may negatively affect the rate of fruit set (Fruit Set in Grapevines 101). Although some clusters with reduced fruit set level were observed, growers did not report reduced crop level. In the Northwest region of PA, 6 and 5 inches of rain were recorded in June and July, respectively.
The best note of the summer was the warm and dry weather conditions observed in August and September in a majority of the state. In Biglerville the cumulative precipitation recorded from April to October was lower than that of the two previous seasons (Figure 3). However, in late September heavy rainstorms came through several areas of PA, raising concerns about bunch rot infections. Indeed some of the white cultivars and most of the reds were still hanging in Central and North PA. Despite the heavy rain, wine grape growers were mostly happy about the health of their grapes. Tony Wolf (Professor of Viticulture and Extension specialist at Virginia Tech University) offered some thoughtful advice on the dilemma: “Should I pick or wait out the rain?” which you can find on Grape Press, page 7 “How to Assess When Rain Threatens” .
Temperatures: High (or above-average) heat accumulation was recorded in many areas of PA in 2015. In Biglerville (South Central PA) GDD accumulation from April 1 to October 30 was 3500 in 2015, compared to 3089 in 2014 and 3270 in 2013 (Figure 4C). Specifically May, August and September 2015 were warmer than in 2013 and 2014 (Figure 4A). In the Northwest GDD accumulation in 2015 (2800) was similar to that of 2013 (2760), but higher than in 2014 (2590) (Figure 4 B). The greatest difference in heat accumulation among the three seasons was recorded in September (Figure 4D). Indeed both white and red wine grapes harvested at the LERGREC in 2015 reached a good level of ripeness.
Insects: Several growers reported problems with Japanese Beetles. Damage was worse than average, and in many cases required extra sprays (for more information please check: What’s Bugging your Vines?). In the Lake Erie region, the severe cold of the past two winters appears to have had no negative impact on populations of the grape berry moth, according to entomologist Jody Timer. Her research has indicated that this insect continues to cause heavy damage in vineyards, particularly in rows bordering wooded areas, and has in some cases made inroads deeper into vineyards over the past two years. It’s imperative to remember that brutal winter temperatures do NOT necessarily reduce the threat of this grape insect pest; grape berry moth is well adapted to life in Pennsylvania and growers will need to continue to be vigilant with regard to timely insecticide applications, regardless of the winter cold.
Fungal disease: Frequent and sometimes heavy rainfall in June and July was very conducive to the development of downy mildew and black rot on fruit (Figure 5). For example, at the Penn State lab at North East (LERGREC), we recorded 10.7 inches of rainfall from June 7 (immediately before bloom) to July 14 (about 3-4 weeks after bloom), that fell on 22 of those 38 days!!! This time period marks the peak period for fruit susceptibility to downy mildew and black rot for all wine grape varieties, and symptoms of these diseases could be found in many (most?) Lake Erie vineyards. In unsprayed research plots of Concord grape where black rot mummies were hung in the trellis (at LERGREC), almost two thirds of the crop was lost to black rot! So, conditions were nearly ideal for the development of this disease in the growing season of 2015.
However, very few serious problems were reported from commercial growers in the Lake Erie region and growers appeared to have, generally speaking, kept these diseases well under control during this challenging fruit loss period. After fruit became resistant, rainfall thinned out during August and September (even though the rainfall total for September was well above average, rainfall frequency was about half that recorded for the fruit susceptibility period). ‘Seasoned’ growers were watching their vineyards closely, and the potential threat of downy mildew leaf infections during ripening did not materialize to any great extent in most vineyards.
Everything we experience in one season is related, to some extent, to what happened in the previous season. For example, when planning your disease control strategy for 2016, keep in mind that inoculum levels for black rot and downy mildew are likely to be starting at higher levels next year, especially if you saw more disease in your vineyard (or your neighbor’s vineyard) than usual in 2015. This means that those first infection periods in spring could be more potent than usual, and if weather is consistently wet, fungicide application timing and frequency, and choice of material, will be more critical. For downy mildew control, be prepared to rotate chemistries to delay the onset of fungicide resistance, especially if you’re using the newer materials (Revus, Revus Top, Presidio, Zampro, any of the strobies, Ranman, Ridomil, and even the phosphorous acid formulations). Be aware that in southern PA there is downy mildew resistance to the strobies in some vineyards already, and that a wet year (and the resulting increased use of strobies to control downy) only serves to exacerbate the problem. On the up-side, we have lots of fungicide options for downy mildew control (as you can see), including the old standards like Captan, copper, Ziram, and any of the mancozeb products that carry a very low risk of resistance development. As for black rot, I know of no resistance problems associated (yet) with our long time ‘heavy hitter’ black rot materials like the sterol inhibitor containing fungicides (Rally, Elite, Mettle, Revus Top, Inspire Super, etc), the strobies, and Captan/Ziram/mancozeb formulations.
So, record your observations of your vineyards from the 2015 season: These are important questions growers should be asking themselves and recording now in order to understand what worked and what didn’t and prepare for the 2016 growing season:
- How well did your weed and canopy management strategies work this season?
- How was the overall vine balance?
- Were there any obvious vine nutrition issues?
- How well did your disease and pest control program work? How much disease did you observe on your fruit, on your leaves?
- Any other important observations or notes.
Final notes on the 2015 harvest: Harvest weather was, for the most part, pleasant. Overall, growers are very happy with the quality of the fruit although in some cases crop level was lower than average due to winter injury. The warm and mostly dry conditions recorded in August and September helped the grapes to reach full ripeness within their specific region with good development of flavor and aromas.
As a general reminder, we will taste a series of the 2015 wines produced from various research trials conducted at Penn State University at the 2016 PA Wine Marketing and Research Board Symposium. We may also feature a few of these wines at various Extension events across the state. You can review some of the winemaking experiments on Denise’s previous blog post: Reflections: Winemaking at Penn State, and we look forward to sharing these wines with many of you in the months ahead.
 Gerling C. (2015) The 2015 Grape & Wine Season: Redefining Normal. Veraison to Harvest issue # 8, pp1-4. Cornell University
 Haggerty L., Martin K. (2015) Concord Crop Average Despite Winter Injury; Niagara Crop Reduced. Veraison to Harvest issue # 8, pp5-6. Cornell University.
 Wolf T. (2015) How to Assess When Rain Threatens Grape Press, The quarterly Newsletter of the Virginia Vineyards Association. Vol. 31 No. 3.
By: Michela Centinari
Denise Gardner, Penn State Enology Extension Associate, and I visited the Lake Erie region, Northwest of Pennsylvania, on June 25 and 26, 2015. We first visited the Lake Erie Regional Grape Research and Extension center (LERGREC) and later met with wine grape growers and winemakers at the South Shore Wine Company. The second day I visited three vineyards with our hosts Andy Muza, the horticulture Extension agent in Erie County, Bryan Hed and Jody Timer, research technologists at Penn State that focus on plant pathology and entomology, respectively.
Regional visits are always a great opportunity to connect with growers and winemakers, discuss production issues, gather information on topics of interest for future educational workshops, and also to learn about grower/winery relationships.
The wine industry in the Northwest region of Pennsylvania is growing, both in size and reputation. Most of the growers I met are experienced juice grape growers transitioning to wine grapes. One of the growers pointed out that he chose, among his 200 acres of existing Concord vineyards, the very best location to plant and grow his Vitis vinifera wine grapes. He had a clear understanding of how site selection is critical to successful cultivation of V. vinifera varieties, and site selection is one of the key areas we discuss with growers upon entering the wine grape industry.
During the two-day visit, most of the discussion focused on winter injury sustained by V. vinifera, inter-specific hybrids and also V. labrusca/native grapevines (mostly Niagara) over the past two winters. The last two years provided record low temperatures in Erie area during the 2013-2014 and 2014-2015 winters, which have proved challenging for farmers (Figure 2). Variation in cold hardiness among grape genotypes, the impact of a diversified crop, and vineyard management practices to reduce/minimize future winter injury losses were discussed to great length.
Growers have been busy assessing the extent of winter injury, training suckers to be used as new trunks and cordons (Figure 3) and making re-planting decisions. One industry member pointed out that winter injury losses have forced growers to make strategic decisions in terms of variety selection. It was recommended that growers use this opportunity to substitute varieties that did not produce well with others that are more suited for the region and individual vineyard sites. In terms of crop diversification, the use of cold-hardy hybrid varieties released by the University of Minnesota may be a viable option for growers, but wineries should be consulted with regards to their interest in those varieties. Local market opportunities still need to be explored in Pennsylvania with regards to cold-hardy hybrid variety sales in the tasting room.
From a research prospective, these two consecutive severe cold winters provided a good opportunity to evaluate the cold hardiness of V. vinifera and inter-specific hybrid wine grape varieties at the variety evaluation planting established at LERGREC in 2008, as part of the NE-1020 multistate project. For more information about the NE-1020 trial, please refer to the article “NE-1020… What? The Top 5 industry benefits affiliated with the NE-1020 variety trial” by Denise Gardner.
During our visit we noticed, as expected, further damage to the cold tender V. vinifera varieties. Among the V. vinifera, Grüner Veltliner and Cabernet Franc are recovering better than Pinot Grigio and Pinot Noir, which are either dead to the ground or showing a weak recovery (Figure 4a, b). Very good bud survival was observed in Chancellor (Figure 4c) which produced about 3-4 clusters per shoot despite the extremely cold events recorded over the last two winters. Overall, Marquette, a cold-hardy hybrid variety released by the University of Minnesota, has shown encouraging results. In addition to the cold sensitive V. vinifera varieties, a poor survival was observed in the NY81.0315.17 (Riesling x Cayuga White) selection (NE-1020 vineyard) and in Traminette at several vineyards within the Erie region (Figure 4d).
Protecting vines and fruiting potential from winter injury
Growers had several questions about best practices to protect trunks and the fruiting potential of the vines against winter injury.
Hilling up the soil around the vines in the fall and taking out hills in the spring is the most common practice used by growers to protect the graft union and some of the scion tissues above the graft union against low winter temperatures. A few growers showed concerns about the wet conditions of the soil in the fall/spring which makes this operation difficult. Heavy, wet soil may be thrown up under the trellis in large clods which can result in imperfect burial of the vine trunk, and makes the take-out operation difficult . Other growers mentioned using straw, or hay, or plowing snow (if there is sufficient snowfall) around the vines to insulate vine tissues. In the spring, it is critical to remove the soil around the graft union to avoid scion rooting, which defeats the purpose of rootstock and may result in vine decline .
Burying sucker canes under the soil or straw in the fall is a method that can be used to avoid winter injury and insure the retention of a ‘marketable’ crop the following year. A comprehensive description of the ‘burial cane’ technique can be found in: Winter Injury to Grapevines and Methods of Protection, Extension bulletin available for $15. Growers in Ontario and in New York State used this technique to protect some fruiting potential of the vines. As a brief explanation, shoots are grown on wires near the ground during the growing season and they are covered with soil or straw in the fall (Figure 5). Another option is to place canes near the ground after the vines go dormant. “A wire on the ground that is tensioned either permanently or temporarily is very helpful to hold canes near the ground” . The buried canes need to be extracted from the soil as soon as the risk of low winter temperatures is past.
The cane burial technique and its effects on vine bud survival and production have been examined at Cornell University with the help of cooperating growers of V. vinifera varieties. For detailed information on the study please check Understanding and Preventing Freeze Damage in Vineyards: Workshop Proceedings (21-38) .
The main finding in this study was:
- Sucker canes buried in the fall do avoid the freeze injury suffered by the aerial canes of the vines.
- After canes were unburied, buds appeared to suffer injury unrelated to freezing. Buried canes showed more “blind nodes,” they were less productive (e., significantly fewer clusters) than canes not buried. Buried canes also showed a delayed bud and shoot emergence compared to aerial, not buried canes.
- Cane burial is not a cheap operation: “typical extra costs per acre for cane burial in the Finger Lakes Region is about $400 to $500. This includes labor needs for laying out ground wire, wrapping them with suckers, hilling, and buried cane extraction, pruning, and tying in spring” .
- “In normal or warm years, burying cane can result in production and economic losses. However, in extremely cold winters, buried canes allow a “half crop” and no dead vines” .
- Zabadal, TJ, Dami, IE, Goiffinet, MC, Martinson, TE, and Chien, ML (2007) Winter Injury to Grapevines and Methods of Protection. Extension Bulletin E2930. Michigan University Extension.
- Goffinet, MC (2007). Grapevine Cold Injury and Recovery After Tissue Damage and
Using Cane Burial to Avoid Winter Injury. In: Understanding and Preventing Freeze Damage in Vineyards, Workshop Proceedings. University of Missouri Extension. 21-38.
By Michela Centinari
It seems like yesterday we were looking at the weather forecast and worrying about cold winter temperature events and the potential for grapevine injury. Now that it is finally starting to get warmer here in Pennsylvania, we may be faced with another threat: spring frost. A grape grower is never bored!
It was another cold winter in Pennsylvania, particularly harsh in the Lake Erie region (Figure 1). At the Penn State Lake Erie Regional Grape Research and Extension Center (LERGREC) temperatures bottomed out at about -21 °F (-30 °C) on February 16, 2015. Unfortunately several cold events (-13, -14 and -15°F) were recorded over the following ten days. On a ‘positive’ note, the week before these extreme cold events, temperatures were lower than normal, with daytime temperature highs well below freezing, except for one day (34°F). These temperatures may have provided a positive, reinforcing maintenance of the vines’ mid-winter cold hardiness . Bryan Hed and the LERGREC’s crew have been checking the extent of bud and trunk damage on Concord and other hybrid varieties.
Information available on cold winter injury on grapevine
At the 2015 Mid-Atlantic Fruit and Vegetable Convention I reviewed the factors that can affect grapevine cold hardiness, explained how to assess bud, cane and trunk cold damage, as well as how to manage cold-injured vines. For information on grapevine cold injury you can refer to the Grapevine cold injury, end of the season considerations blog post and references within.
If you are looking for specific information on winter injury to vine phloem you can check this recent and comprehensive review: Viticulture and Enology Extension News, spring 2015, Washington State University written by Michelle Moyer (Assistant Professor and Viticulture Extension Specialist at Washington State University).
Percentage of winter injury does not equal percentage of crop loss
In March, I attended The Northern Grapes Project Symposium in Syracuse, NY. Tim Martinson (Senior Extension Associate at Cornell University) and Imed Dami (Associate Professor and Viticulture Extension Specialist at Ohio State University) highlighted that the percentage of bud cold damage does not always equal percentage of crop loss. The answer often lies in the pruning adjustment strategies adopted by growers. Dami reported that, despite 40% of bud winter damage, Marquette produced about 5 tons/acre in Ohio last year. Those vines were pruned to 5 bud-spurs (‘hedge pruning’) to compensate for winter injury . .
Tim Martinson reported that last year many growers in the Finger Lakes region (NY) left more buds to compensate for winter injury experienced during the 2013-2014 winter. The growers left up to five-fold more buds than they would have done in a normal year. Many cane-pruned VSP vineyards were spurred to 5-6 bud spurs. It was a pleasant surprise that in 2014 widely planted V. vinifera varieties such as Riesling, Chardonnay, and Cabernet franc, came through better than was expected based on bud mortality estimates. I know that many growers prefer cane pruning, and I understand the reasoning behind that, but please take into consideration that cane pruning is not recommended following winter injury .
How to train suckers of cold injured vines?
Imed Dami recommends that growers “actively” train vines back to their original training system in the same season in order to resume production quicker. Therefore, instead of training suckers vertically (they can become extremely vigorous!) they should be trained horizontally along the fruiting wire. With extremely vigorous vines, four shoots should be selected and then two can be laid horizontally on the fruiting wire. With less vigor, two shoots can be selected and laid horizontally, one to each side. Then, shoots should be tipped to stimulate lateral shoot growth. Lateral shoots growing vertically and upward will become the future spurs next season . Latent buds on the lateral shoots will develop like buds from primary shoots. As long as they are exposed to sunlight and clean from disease and insects, they should have the same cold hardiness as any other buds.
Here is a valuable video regarding pruning with regards to cold injured vines: https://www.youtube.com/watch?v=r1Yhv8Rw38o
A few words on spring frost
As we get close to bud-break, the threat of spring frost is approaching. In the spring of 2014, no frost damage was recoded in grapevines in Pennsylvania and hopefully we will have another frost-free spring. If you would like to get information about frost protection strategies you can check the following websites and newsletters. Unfortunately, there is no new exciting or infallible frost protection method. Site selection remains the best way to protect vines from frost injury.
- Frost Injury, Frost Avoidance, and Frost Protection in the Vineyard, eXtension website, by Ed Hellman, Texas AgriLife Extension
- The ABCs of Frost Management by Robert Evans, Supervisory Agricultural Engineer with the USDA-ARS (retired)
- Viticulture Notes Vol.30, April 2015 by Tony Wolf, Professor and Viticulture Extension Specialist at Virginia Tech University
- Comprehensive presentations on active and passive frost protection strategies can be found at the University of California, Davis Cooperative Extension website
To the often asked question: If my vine gets frosted, should I remove the injured shoots?
The answer is: “There’s not much of a point,” according to Tony Wolf, Professor and Viticulture Extension Specialist at Virginia Tech University. A detailed explanation on how to handle damaged shoots and potential consequences on yield production can be found at Viticulture Notes, Vol.25, May-June 2010
Testing the cryo-protectant properties of KDL
KDL (potassium dextrose lactose; Agro-K corporation, Minneapolis, MN, USA) is a potassium based fertilizer. According to the manufacturer’s literature, spraying KDL shortly before a frost event (24-48 hours) would increase the potassium and sugar levels within the plant and reduce the frost injury on young vine tissue. Although attractive to growers, there is not scientific literature that supports the effectiveness of this product in preventing/reducing frost damage. Numerous grower testimonials are available, but growers usually do not leave an ‘untreated’ control area where the material is not applied, which is critical in order to evaluate the efficacy of KDL as cryo-protectant.
A large scale study coordinated by Tim Martinson (Cornell University) and in collaboration with the Agro-K company (KDL manufacturer) has been set up this spring to evaluate the effect of KDL at several vineyard sites located in NY and PA. Penn State is a collaborating university that is helping to work with six commercial growers that agreed to participate in the study in addition to the Penn State LERGREC in North East, PA.
Although, I’m hopeful there will not be a spring frost that growers have to deal with, if we do end up with a spring frost during the 2015 growing season, this study will hopefully provide some useful recommendations for grape growers.
- Wolf T.K., 2015. Viticulture Notes. Vol. 30 supplement, 17 February 2015
- Dami, I.E. , Ennahli S., Zhang Y. (2012). Assessment of winter injury in grape cultivars and pruning strategies following a freezing stress event. American Journal of Enology and Viticulture, 63: 106-111.
- Dami, I.E. 2009. Ohio Grape-Wine Electronic Newsletter Vol.3: 2-5, 6 Feb 2009.
- Dami I.E., 2014.Ohio Grape-Wine Electronic Newsletter, Vol.25, 3 July 2014.
By: Michela Centinari
I imagine as winter approaches one thought on every grower’s mind is: “Is this winter going to be anything like the previous one?”
The winter of 2013/2014 was one of the most severe since 1994 and we can hope another 20 years or more pass before we must endure another of the same magnitude. The extent of damage and crop loss varied among regions, individual vineyard sites, wine grape varieties (Figure 1) and the health of the vines going into the cold season. In this regard, during a vineyard visit in Chester County (Southeast Pennsylvania) in August, a grower pointed out a block of Cabernet Franc (Vitis vinifera L.) vines with winter cold injury symptoms. The vines had a healthy green canopy but, surprisingly, no clusters. That was unusual because other Cabernet Franc vines in the area were fine. However, the grower highlighted that those vines had already experienced severe frost damage in the previous spring (2013). Frost damage may contribute to a low overwinter carbohydrate reserve and negatively affect bud cold hardiness as well as the development of shoots and inflorescences in the following spring. Concentrations of non-structural carbohydrates are closely related with cold hardiness in grapevine buds and canes .
Could delaying fruit harvest for ice wine production negatively affect vine health and compromise winter bud cold-hardiness?
A recent 5-year study conducted in Ohio reported that neither crop level (16 vs 32 clusters per hedgerow meter) or harvest date (beginning of October vs middle of December) had an impact on winter bud cold-hardiness in ‘Vidal blanc’ vines . This is very good news for growers. However, as the authors suggested, the effect of crop level on cold hardiness may depend on the variety  and its vegetative and reproductive characteristics (i.e., tendency for excessive vigor and/or over-cropping).
Ongoing research at Penn State is being conducted to assess the impact of crop load management practices on bud cold acclimation, de-acclimation, and maximum cold hardiness, as well as carbohydrate reserve storage. We plan on highlighting these developments as results are determined over the next few years.
How to assess cold injury in grapevine, and manage cold injured vines?
After budbreak, when the extent of the damage started to become more clear, many growers wondered how to assess the extent of the damage and what the best practices were for rapid vine recovery. Our grape and wine team at Penn State put together a list of resources to help growers during this difficult growing season. Here are some of those resources:
You can start reading the article published on eXtension Cold Injury in Grapevine by Mark Chien, former Penn State Viticulture Extension educator and now Program Coordinator, Oregon Wine Research Institute, and Michelle Moyer, assistant professor at Washington State University. At the end of the article you can find of comprehensive list of recommended resources that can be used to assess and manage cold damage in the vineyard. Among these resources I would like to highlight:
- Winter Injury to Grapevines and Methods of Protection by Tom Zabadal, Michigan State University;
- Assessing and Managing Cold Damage in Vineyards, Washington State University
- Evaluating bud injury prior to pruning Part 1 and Part 2; two brief video presentations from the Finger Lakes Grape Program;
Other resources that you may find useful are:
- Managing Winter-Injured Vines published on Appellation Cornell, June 2014, by Tim Martinson (Senior Extension Associate, Cornell University);.
- Managing Winter Injury published on the Lake Erie Regional Grape Program, Cornell University, Viticulture Notes, Issue # 3, June 2014, by Kevin Martin (Penn State University, LERGP Business Management Extension Associate). The article provides useful guidelines of the cost associated with re-training and re-planting a vineyard.
What did we learn?
The severe cold winter provided a good opportunity to evaluate the cold hardiness of Vitis vinifera and inter-specific hybrid wine grape varieties at the two variety evaluation plantings established in Pennsylvania (PA) in 2008, as part of the NE1020 multistate project. The two plantings are located at the Lake Erie Regional Grape Research and Extension Center (LERGREC, Northwest Pennsylvania) and at the Fruit Research and Extension Center (FREC) in the southern side of PA. For more information about the NE-1020 trial please refer to the article “NE-1020, What? The Top 5 Industry Benefits Affiliated with the NE-1020 Variety Trial” by Denise Gardner.
At the LERGREC station all the V. vinifera varieties experienced extensive winter injury. High incidence of vine mortality was recorded in Syrah, and Muscat Ottonel; trunk injury was mostly observed in Pinot Noir and Pinot Grigio. Among the V. vinifera varieties, Cabernet Franc and Grüner Veltilner vines are recovering the best; healthy suckers are growing from above the graft union and they will be used for trunk renewal next spring. For information regarding the level of bud injury observed on the 17 grapevine varieties established at the LERGREC site please refer to the article “Grape Growing in PA In Spite of the Weather” by B. Hed and M. Centinari
As expected, lower levels of winter injury were recorded at the FREC station in the Southern part of Pennsylvania. The most significant winter injury was observed in Tannat (almost 100% vine mortality). Some of the other varieties experienced cold damage, limited primarily to primary buds. Although, some of the Syrah and Malbec vines suffered conductive tissue damage (phloem and xylem) and collapsed during the summer (Figure 2).
As a consequence of primary bud damage some of the V. vinifera varieties produced low crop yield (Table 1). Specifically, average yields of Malbec, Albarino and Cabernet Sauvignon were much lower than those of the previous season (second column, Table 1). Cluster number per vine in Sangiovese and Viognier were lower than usual. Data such as “percent live buds per total buds left (% live buds/total buds)” and “shoot number per vine” were also recorded. This will provide a comprehensive picture of the differences among the genotypes and their ability to adapt to extreme environmental conditions such as the cold temperatures we experienced in the winter of 2014.
Table 1. Yield components of 20winegrape cultivars in the NE-1020 cultivar trial at Fruit Research and Extension Center (FREC) in the southern side of PA. Vines spacing is 6’ between vines and 9’ between rows.
- Jones, K.S., J. Paroschy, B.D. McKersie, and S.R. Bowley (1999). Carbohydrate composition and freezing tolerance of canes and buds in Vitis vinifera. J. Plant Physiol. 155:101-106.
- Dami I.E., S. Ennahli, and D. Scurlock (2013). A Five-year Study on the Effect of Cluster Thinning and Harvest Date on Yield, Fruit Composition, and Cold-hardiness of ‘Vidal Blanc’ (Vitis spp.) for Ice Wine Production. HortScience 48(11):1358–1362.
- Dami, I.E., D.C. Ferree, S.K. Kurtural, and B.H. Taylor (2005). Influence of cropload on ‘Chambourcin’ yield, fruit quality, and winter hardiness under midwestern United States environmental conditions. Acta Hort. 689: 203–208.
By: Bryan Hed
Throughout this grape growing season, we are reminded of the extreme cold temperatures earlier this year that damaged grapevines in many eastern US vineyards, especially those of Vitis vinifera. In addition to outright death of vine trunks and arms, there has been the widespread appearance of crown gall. What’s the connection? The pathogen causing crown gall is a bacterium, Agrobacterium vitis, that can be present in vines for years without causing any disease symptoms until a trunk damaging event occurs like the extreme cold brought on by the polar vortex in January. In spring, as cambium cells attempt to restore cold damaged vascular tissue, the bacterium causes the multiplying vine cells to create masses of unorganized callus tissue instead of new vascular tissue. Therefore, instead of repairing the conductive capacity of damaged vine trunks, the growth of callus tissue (the galls) progressively compromises injured conductive tissues and leaves many vines weak or dead. So, the presence of the bacterium does not in itself cause crown gall, but the susceptibility to crown gall is related to susceptibility to winter cold damage and we often find varieties of Vitis vinifera to be most affected by this disease in cold climate viticulture. Susceptibility among hybrid wine varieties can vary greatly and natives, like Concord, appear to be among the least affected. There may also be varietal differences in the tolerance to crown gall. For example, in our Vitis interspecific hybrid ‘Chancellor’ vineyard, most vine trunks appear to have exploded in crown gall this summer, and yet not a single vine has collapsed, canopies are lush and loaded with crop, and we hope to mature and harvest that crop. In contrast, in our Vitis interspecific hybrid ‘Chambourcin’, many galled vines have either collapsed or are turning yellow despite aggressive crop thinning, and the fate of that crop hangs in the balance. Site factors may also play a role in crown gall development as they affect low temperature extremes. Sites that minimize winter cold extremes will minimize problems with crown gall. There is no cure for crown gall and a vine that develops crown gall may die within the current season, or linger for a few seasons before collapsing. The speed at which galled vine trunks collapse within a season may be affected by stress factors, particularly availability of water.
Regardless of how quickly the disease is progressing, replacement of whole vines or galled trunks of infected vines will be necessary to maintain optimal vineyard productivity. If galls appear on newly planted vines, it would be best to replace them rather than spend time trying to renew them. When removing vines, it is important to extract as much of the root system as possible as the bacterium can be present in roots and remain viable in the soil for many years. For this reason, there is no guarantee that replacement vines won’t become infected from A. vitis bacteria already in the vineyard soil. On the other hand, older established vines can often be renewed if the rootstock is healthy and they are throwing healthy shoots from the scion below the galls. These scion shoots or suckers can be trained up to become new trunks. For example, ten years ago a rough winter at our site in Erie county caused our mature Chambourcin block to explode with crown gall; we had no idea crown gall infection was so widespread in the block. However, rather than starting over, crown gall expert, Dr. Thomas Burr, advised us to train up new vine trunks from suckers emanating from below the galls, and we enjoyed many more years of full production from that block. Unfortunately, 10 years down the road, we are now faced with repeating that renewal task. If you choose to renew, you have some options. If the old trunks are dead or obviously dying and will not ripen a crop, you can remove the old trunks now or at your convenience. On the other hand, if galled vines have developed some canopy on the old trunks, or if galled vines still appear reasonably healthy otherwise, you can leave the old trunks as (i) a support for training of new trunks (ii) as a competitive sink to reduce overly vigorous sucker growth (which will result in poor quality renewals), and (iii) as a means of harvesting some crop from what remains of the tops, if it appears cost effective to do so. In this case, old, still living trunks can be removed later during dormant pruning or in successive seasons, when new trunks are ready to make up a reasonably full complement of buds.
For the future, if you’re growing cold sensitive varieties (especially V. vinifera) in the northeastern U.S., maintain multiple trunks and expect to do regular trunk renewal as standard procedure. For grafted vines, hilling soil to bury grafts in fall will help to ensure the survival of scion buds for trunk replacement.
Down the road, through the Clean Plant Network and funding from USDA, a clean vine program is well underway to make ‘crown gall free’ vines more available from nurseries. I am told the new Farm Bill will provide funding over the next five years for this work to continue. The goal is to enable growers to start with a crown gall-free vineyard. And while we are not there yet, detection of crown gall in grapevines continues to improve, making the work of establishing clean mother blocks more trustworthy. Though the main source of crown gall remains infected nursery stock and nurseries may not yet be able to guarantee crown gall free planting material, the quality of planting stocks continues to improve.
For further information, these are some excellent references:
- Winter injury of grapevines. 2007. T. Zabadal et al. (eds.) 106 pps. Michigan State University.
- Tim Martinson and Thomas Burr. How Close are We to Crown Gall-Free Nursery Stock? Appellation Cornell; Research Focus 2012-1. http://nationalcleanplantnetwork.org/files/144948.pdf
By: Bryan Hed and Michela Centinari
The winter of 2014 will be remembered as one of the harshest for Pennsylvania grape growers. To begin with, the polar vortex that brought the ‘arctic’ to Pennsylvania in early January, caused severe damage to many wine grape varieties, especially cultivars of Vitis vinifera. During that event, temperatures in the Lake Erie region of Pennsylvania, fell from 47 F to below zero within 16 hours. Temperatures bottomed out at about -12 F (-24 C) and remained below zero (F) for about 20 hours. This was followed by steadily rising temperatures over the next several days, warming back up into the 50s. But the rollercoaster ride didn’t end there; there were several more severe cold events over the next 8 weeks as wave after wave of frigid air flowed through Pennsylvania vineyards. Our initial mission was to assess the damage to grape buds and compare the hardiness of the many grape varieties grown at two of our research farms: Rock Springs near the main Penn State campus (dead center of the state) and the Lake Erie Regional Grape Research and Extension Center in Erie county (northwestern corner of the state). Weather stations at both locations enabled us to track daily low temperatures through the period of the most intense cold (Figure 1 &2). As the ‘bad news’ came in regarding bud and vine cold damage, we began to rethink our plans for the 2014 growing season and see what we could learn from it. Our initial data are presented in the figures below.
Bud survival on different node positions among different dormant pruning strategies (Erie site).
As spring sprang, we began collecting data on Chardonnay and Riesling at the Erie site, examining shoot emergence at different node positions after the application of three different pruning strategies. Patterned after work conducted several years ago by Dr. Imed Dami on Pinot Gris in Ohio (Dami, 2012), we examined the effects of (i) no pruning, (ii) pruning to 5-6 bud spurs, and (iii) pruning to 2-3 bud spurs. Vines in our Chardonnay block had taken a major hit from severe cold over the winter and bud break was delayed with the loss of nearly all primary buds. Gradually, secondary and tertiary shoots appeared from a few node positions and percent bud survival (buds producing a shoot) among the different pruning treatments varied from 17% (average of first 10 nodes on non-pruned vines), to 21% (average of first 5 nodes on 5-6 bud spurs) to 26.5% (average of first 3 nodes on 3 bud spurs). Primary bud survival was thought to be less than 1%: of 2,600 nodes examined, only 5 produced shoots with two clusters (0.2%) and 11 produced shoots with one cluster (0.4%). Vines pruned to 2-3 bud spurs showed the highest percent bud survival among the most basal 3 nodes and shoot emergence at node position 2, was significantly higher on vines pruned to 2-3 bud spurs, when compared to ‘no pruning’ and ‘pruning to 5-6 bud spurs’. Among vines pruned to 2-3 bud spurs, shoot emergence at node position 1 (35 %) was significantly higher than shoot emergence at node position 3 (20%). Among non-pruned Chardonnay vines, there were no significant differences observed in bud survival among any of the first (most basal) 10 node positions.
Riesling vines appeared to suffer less severe winter cold damage than Chardonnay. Percent Riesling bud survival among the different pruning treatments varied from 24.3% (average of first 10 nodes on non-pruned vines), to 38.8% (average of first 5 nodes on 5-6 bud spurs) to 50.7% (average of first 3 nodes on 3 bud spurs). Of 1300 Riesling nodes examined, 6.5% produced shoots with one cluster, and 13.5% produced shoots with two or more clusters. So, about 20% of Riesling nodes examined were fruitful, whereas just 0.6% of Chardonnay nodes examined, were fruitful. Some trends in Riesling were similar to Chardonnay, where the highest percent bud survival (buds producing a shoot) among the most basal 3 nodes occurred among vines pruned to 2-3 bud spurs (44% (no pruning) and 47% (5-6 bud spurs) compared to 51% (2-3 bud spurs)). Among non-pruned Riesling vines, node 1 showed significantly higher survival (64% of nodes producing a shoot) than nodes 2 through 10 (which were not significantly different from each other).
Percent bud survival among different grape varieties at Rock Springs and Erie
As expected, there was tremendous variation in bud survival among the many grape varieties at the two research stations (Figure 3&4).
At Rock Springs in the center of the state, the most severe damage was observed in cultivars of Vitis vinifera, whereas French hybrids like Noiret, Corot Noir, La Crescent, Arandell, and Marquette showed fairly high levels of bud survival.
At the Lake Erie Regional Grape Research and Extension Center (Erie county; northwestern corner of the state), similar trends between V. vinifera and French hybrid/Native American varieties were observed. Old standards like ‘Vignoles’ and ‘Chancellor’ and the Minnesota hybrids were the winners, and appeared to fare as good as or better than even native varieties like Concord and Niagara. At both locations, Riesling, though seriously damaged, was generally the winner among the cultivars of V. vinifera.
Throughout the season, we will continue to evaluate the recovery of the different varieties and the effects of different pruning strategies in our Penn State research vineyards. Vine renewal will be a primary objective in many of our vineyard blocks. Sucker growth appearing at the base of our V. vinifera cultivars and our more heavily damaged hybrids, will be groomed as trunk replacements for 2015.
We are also beginning to see outbreaks of crown gall at the base of trunks where winter trunk damage has occurred on vines infected with the crown gall bacterium (Agrobacterium vitis). Some varieties, like Chancellor, are very susceptible to crown gall, and winter trunk damage may result in collapse of otherwise healthy looking vines with full canopies and full crops. So, don’t be too hasty to remove all sucker growth from otherwise healthy looking vines until you are reasonably sure the trunks are not developing crown gall. You should be able to observe new gall development on crown gall infected vines before the end of June (NOW). Areas developing galls will appear unnaturally swollen and the bark will appear to be splitting. New gall development can be detected if the bark is peeled from these swollen areas. The outside of new galls may initially appear dark on the surface, but the fresh white gall tissue beneath can be revealed with the scrape of a fingernail. If you find yourself renewing trunks on crown gall infected vines, always make sure to select scion-wood sucker growth emerging from below the gall affected area. Trunks with galls do not have to be removed this season, but can be retained for now to produce a potential crop and as a means of support for fastening suckers/new trunks. Diseased trunks can then be removed during winter dormant pruning, and replaced by the new trunks.