Vole Damage in Vineyards

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

I received a number of reports of vole damage in vineyards throughout the Willamette Valley this season. Evidence of their presence became visible in August with feeding damage to trunks (Figure 1) and within the canopy, including damage to shoots and rachises of grape clusters (Figure 2). Voles eat vegetation and typically feed on roots or the base of trunks. Voles do not typically cause issues until a population peak and/or environmental conditions allow for habitation. They may reach epidemic-level populations every ten to 12 years, but these population surges are not predictable and last for one year (Gunn et al. 2011). The Willamette Valley’s last reported vineyard infestation occurred in 2005, and some vineyards lost vines due to the damage.

Preventing and eradicating voles.  Our best suggestions to growers who have been observing vole presence in vineyards has been to encourage eradication. Trapping or baiting voles may not be practical on large acreage or advised with certain farming certifications. For example, zinc phosphide is not allowed in organic production. However, soil tillage or mowing may provide some level of prevention and control. Research in field crops show that tilling the soil is the most effective method of reducing vole populations (Jacob 2003), by disturbing their burrows and causing movement to other vegetated areas. Voles avoid bare ground, so tillage can prevent habitation altogether. In the Jacob (2003) study, they found voles disappeared altogether after disking to a depth of 19 inches. Mowing vegetation was found less effective than tillage, as the mulch from mowing allowed sufficient cover for the voles and did not encourage movement away from the cropped areas. Avoiding mulch layers or vegetation growth under-vine will prevent voles from inhabiting the areas near grapevine trunks and feeding on roots and trunks when food sources are limited.

Scouting for damage. Voles tend to feed on vine roots and at the base of trunks. Look for feeding damage at and just below the soil surface. Since the feeding typically occurs through the phloem and vascular cambium, the cell layers that lie between the phloem to the exterior and xylem to the interior, the vascular system is compromised. As a result, affected vines may turn color abruptly (yellow or red, Figure 3), as they have limited ability to move photosynthates (sugars) and mineral nutrients through the vines to the roots once the phloem and cambium are damaged. Roots are actively acquiring carbohydrates and mineral nutrients from the canopy during late season in preparation for the next year. Having this connection severed is a major issue.

Can anything be done to repair damaged vines? Vines with girdled trunks and root damage may not survive if the damage is done to the circumference of the vine. This is due to the lack of vascular cambium to grow new phloem tissue and “heal” the wound. The best thing to do at this time is flag vines with damage now and check back later in winter during pruning and early spring. If damage was only apparent in the canopy (rachises, berries, and shoots), vines may be able to be pruned to healthy tissue in winter. However, also be sure to flag these vines for follow-up.

Because voles do not hibernate, high populations this winter may pose a threat to vines if they continue feeding in areas where they were observed this season. It will be important to remove vegetation by way of tilling soil or removing mulch layers or vegetation under-vine to avoid any further damage.

Literature Cited

Gunn D, Hirnyck R, Shewmaker G, Takatori S, and Ellis L. 2011. Meadow voles and pocket gophers: Management in lawns, gardens, and cropland. University of Idaho, PNW 627.

Jacob J. 2003. Short-term effects of farming practices on populations of common voles. Ag Ecosyst Environ 95:321-325.

 

Figure 1. Vole damage to the base of a trunk on a mature grapevine. Photo courtesy of Ryan Wilkinson.

 

Figure 2. Feeding damage is apparent on the top of the grape cluster’s rachis (peduncle) and the lower portions of the shoot from which it originates. Photo courtesy of Ryan Wilkinson.

 

Figure 3. Vines with vole damage to the trunk show almost complete reddening of the canopy in Pinot noir vines. Photo courtesy of Ryan Wilkinson.

 

Resistance is Futile? Strobilurin resistance presence and persistence

Dr. Walt Mahaffee, Research Plant Pathologist, USDA- ARS

In 2015, we found widespread Strobilurin (QoI) resistance in Oregon, and subsequently in California and Washington when we surveyed viticulture regions in those states, it probably seemed like the sky might be falling.  Then when we showed that greater than 70% of the QoI resistant population was tolerant to very high doses of DMI (higher than can be legally applied); it really seemed like the sky would fall.  However, there was a silver lining. We kept all the DNA from all the inoculum monitoring (spore trapping) we had been doing since 2007.

We analyzed all those samples for presence of the genetic mutation responsible for the QoI resistance and found some interesting results. First, we weren’t able to detect QoI resistance before 2013. Second, we detected QoI resistance at least two years prior to growers reporting management problems. This means we had a tool to monitor resistance development which could be useful for warning growers of resistance developing.

Another remarkable finding was that the number and frequency of detecting resistant spores was much lower than the wild-type spores even when QoIs were being used in the vineyard, and we found far more resistant colonies than wild-type on leaves.

These results indicated that there might be a fitness cost to the mutation causing QoI resistance. Given that the mutation alters a protein involved in fungi producing energy, it makes sense that the fungus would not grow as well. This should also mean that moving away from using QoIs should allow the wild-type to out-compete the QoI resistant isolates, and eventually QoIs would become effective management tools again. Sarah Lowder, a PhD student, also made another discovery this past winter – Chasmothecia (the mildew overwintering structure) of QoI resistant populations do not survive as long as wild-type populations. This is more good news.

Now the big question is how to determine how long we need to rotate away from using chemistries with resistance and how to determine when we can use them again. That will be the future work of three graduate students in the lab.

Sarah is going to be working on how to rapidly and efficiently monitor for resistance. She has already made significant advances in this area. Sarah’s work this summer shows that we can swab worker gloves after manipulating the canopy (e.g. shoot thinning, lifting wires, leaf pulling, dropping crop, etc.) and get estimates on the presence of mildew and its resistance. These results are similar to spending hours scouring for mildew colonies. Sarah also developed a simple procedure to test for potential resistance by collecting bark in the winter. Simply grab bark off several vines and stuff it into a mason jar, add ice cold bottled water, shake, then decant through mosquito netting. The material adhering to the net can then be processed using our molecular assays.

Next, Chelsea Newbold (a new MS student) will be examining how the QoI resistance mutation impacts colony formation and sporulation in relation to various environmental conditions?  The big question is can we make predictions about the potential for field failures similar to how we estimate disease risk with the disease forecasting models.

Alex Wong (a new PhD student) will be looking at how fungicide resistance persists and transfers through a population. We need to understand this because resistance to other fungicides will develop, and we will need to know how to manage these resistant populations while they are still in the minority.

Since you might be wondering, here is the results of our 2018 survey for QoI (G143A) resistance. These data are thanks to funding from the Oregon Wine Board, American Vineyard Foundation, and Washington State Wine Commission. It is also a product of numerous folks in each region taking the time to send in samples.  If you would like to send sample, please contact us walt.mahaffee@ars.usda.gov and we will send you kits and instructions.

Figure 1.  Sample frequency categorized as containing only grape powdery mildew with wild-type genotype
(QoI sensitive – green), the G143A mutation for resistance (QoI Resistant – red), sample having both wild-type and
resistant genotypes (yellow) and no GPM detected (purple) in the sample.  Several Oregon vineyards are scouted
on a bi-weekly basis with extensive swab sampling leading to numerous no detection of mildew – that is good news
– since no mildew was found with the early scouting either.

Managing mycorrhizal fungi and soil health in vineyards

Dr. R. Paul Schreiner, Research Plant Physiologist, USDA-ARS

Renewed interest in vineyard soil health driven in part by advances in microbiome research provides a rationale for reviewing what we know about the foremost component of the root microbiome in grapevines, the arbuscular mycorrhizal fungi (AMF). While other soil bacteria and fungi play important roles in vineyard health and productivity, AMF are unique because of the broad range of benefits they confer. These benefits include improving nutrient uptake from soil (particularly phosphorus (P) and other less mobile ions), increasing soil carbon storage, maintaining soil aggregate stability, and increasing tolerance to drought and pathogens. In the red hill soils of western Oregon, grapevines cannot obtain enough P to grow beyond a few nodes if AMF are absent. They are an integral component of grape and wine production here, and how we treat our soils and vines influences their abundance and the benefits they can provide. There are a few basic issues for viticulturists to consider in managing AMF to get the most from our below-ground fungal partners. These fall under pre-plant and post-plant considerations.

Pre-plant AMF Management.  The key pre-plant issue is whether or not the population of AMF is ample enough to ensure that vine roots are quickly colonized. In most cases the answer to this question is yes. AMF are naturally present in almost all soils worldwide because over 80% of all plant species form this type of mycorrhizal association. However, in modern farming systems certain practices can destroy or greatly reduce AMF in soil. While their use is rare in viticulture, pre-plant soil fumigants (methyl bromide, metam sodium, dichloropropene/chloropicrin, and dimethyl disulfide) typically used to control nematodes and soil-borne fungal diseases can wipe out AMF populations. AMF can also be reduced if host plants are absent for an extended period prior to planting a new crop. This can result from long term fallow periods or from the cultivation of non-host plants. Work in Australia to understand the phenomenon of “long fallow disorder” showed that a fallow period of 1 year or more reduced AMF propagules in soil resulting in poor AMF colonization and P deficiency in subsequently planted crops. Soils from long fallow plots could be rescued by adding AMF back to the system from recently cropped soils. Weeds can also maintain AMF populations in soil and may be important in some cases. For example, my lab showed that soil solarization conducted in the summer reduced AMF populations the following spring in western Oregon because solarization suppressed weeds over the fall and winter that acted as bridge to maintain AMF. Growing cash crops or cover crops that are not hosts for AMF can also reduce AMF propagules in soil. A number of plant species do not form mycorrhizal associations of any type or form other types of mycorrhizas that will not maintain AMF propagules in soil. Common ones used as cash crops or cover crops in agriculture are the mustards (Brassicales) including numerous vegetables, rapeseed, and meadowfoam, as well as spinach, buckwheat, amaranthus, and lupine. A new vineyard planting that follows these crops may benefit from adding AMF at planting or boosting the native AMF population by growing a host plant cover crop before planting. Planting a vineyard after hazelnuts is the most likely scenario where adding AMF will be needed in western Oregon because hazelnuts are ectomycorrhizal and because the orchard floor is kept bare for many years (not allowing host plant weeds or cover crops to maintain AMF).

Exactly when the AMF population is too low for healthy vine establishment is not clear. I conducted numerous AMF inoculation trials when I first began working on grapevines over a decade ago in nurseries and new vineyards. Results from the vineyard trials showed that inoculation with AMF (produced in my lab) enhanced root colonization and improved vine growth in only one of five experiments conducted in the Willamette Valley. By year 2, however, the non-inoculated control vines no longer differed from inoculated ones, and in no case in the nursery or vineyard was vine survival significantly altered by inoculating with AMF. Viable AMF were present at all the sites where we conducted inoculation trials so that the control vines became colonized at every site to at least a small degree.

Post-Plant AMF Management.  Even though grapevines rely heavily on AMF to obtain ample P and often other nutrients, they also can reduce the extent of AMF colonization within their roots when nutrient status (particularly P) is high. Therefore, avoiding fertilizer applications unless a nutrient is demonstrated to be low or deficient is a good practice to reduce negative impacts on AMF. For example, AMF colonization of Pinot noir roots was reduced in vineyards receiving foliar P fertilizer sprays. Root colonization was also negatively correlated to leaf P and leaf nitrogen (N) concentrations across a survey of 31 Chardonnay and Pinot noir vineyards in the Willamette Valley. There is evidence from other farming systems that organic forms of nutrients are less harmful to AMF than synthetic fertilizers, but even organic sources including manure can reduce AMF and potentially reduce other benefits they provide if applied at high rates.

Soil applied fungicides will obviously harm AMF, but what about foliar fungicides? At this time, there is no evidence that the fungicides used in our spray programs to control powdery mildew and grey mold have a negative impact on AMF. However, reducing tillage can benefit AMF because tillage breaks up their hyphal networks in soil. Indeed, we showed that in-row cultivation reduced AMF colonization in Oregon vineyards as compared to herbicides (mainly glyphosate) used to suppress in-row weeds. Finally, in separate studies both east and west of the Cascades, AMF colonization in grapevine roots was lower in vines at wetter sites (west) or in vines that received more irrigation water (east). Therefore, applying less water will also enhance AMF in vineyards. Since AMF provide other benefits beyond their key role helping grapevines obtain P, choosing management options that enhance their abundance (or at least do the least harm) also improves other aspects of soil health.

Wine Clubs – Can we do better?

Dr. James Sterns, Associate Professor, Department of Applied Economics, Oregon State University

The 2018 Direct to Consumer Wine Shipping Report, published collaboratively by the information technology company SOVOS and the trade publication Wines & Vines, has just been released and an overriding message within it is clear – Direct to Consumer (DtC) sales are growing rapidly in both volume and value of sales. The reported numbers are eye-catching: total U.S. consumer spending in 2017 on DtC wine shipments of $2.69 billion, with 5.78 million cases shipped. And reading further into the report, there are even more impressive quotes to be found:

  • “Oregon is clearly having its day. Due to larger than average harvests in 2013-2015, along with increased attention from investors, the trade, media and consumers, Oregon’s sales and shipments are flourishing.”
  • “Since 2012, the volume of wine shipments from Oregon wineries has increased by 214%, with the value of those shipments increasing by 227%…Oregon kept rolling in 2017, delivering the greatest DtC shipping increase of all six regions tracked.”
  • “As in past years, the small winery (5,000 to 49,999 cases) and very small winery (1,000 to 4,999 cases) categories drove the DtC shipping channel, accounting for 70% of the value of U.S. winery shipping.”
  • “By nearly every measure, the winery DtC shipping channel continues to outperform every other retail channel in the United States, be it grocery stores, independent fine wine shops or convenience stores.”
  • “…tasting rooms and wine club sales still drive the lion’s share of DtC growth…”

With news like that, Oregon wineries are obviously aware of and intent on continuing their efforts to sell more wine directly to the consuming public. But there remains an open question about at least one component of DtC marketing, and it’s a question that I have heard repeatedly in the past 18 months. It’s a sentiment shared by many Oregon winery owners and managers. Simply put, there’s a shared sense that, “we really don’t know that much about how to effectively manage our wine clubs.”

As part of a new OWRI initiative, my colleague Catherine Durham and I are studying how wine clubs throughout the state of Oregon are managed, and more importantly, what are the preferences and motivations of wine club members. This research is progressing through two phases – first, this past Fall we solicited responses to a questionnaire from Oregon wineries about how they manage their wine clubs.  These results are in and are helping to inform our next phase of research – sending questionnaires directly to wine club members, asking them about their participation in wine clubs. Our lines of inquiry are focusing on the following: What features and benefits of club membership do they value most?  When and why did they join the wine club, and what incentives will motivate them to stay in the club? How many clubs have they participated in, both historically and currently and what has motivated them to change or leave a club?

We know of at least one other recent project that asked similar questions. A study published by researchers at Sonoma State University was based on a small sample of 25 students majoring in wine business, which limits how much we can generalize the findings. And yet their study does help support our efforts, in part by identifying a set of common wine club attributes, which included wine club levels (ranging from one to six), ways to differentiate across wine club levels (most commonly by price points), allowing customized ordering, the number of shipments per year (ranging from one to six), the number of bottles per shipment, price range of bottles shipped, and associated tasting room benefits (such as allowing non-club members accompanying club members in a tasting room complimentary tastings and/or discounts). These are some of the specific topics that we plan to include in our club member questionnaire.

We hope to have the club member survey ready to use within the coming weeks. We will be completely dependent upon the cooperation of Oregon wineries and their wine club managers to distribute this questionnaire. In appreciation of the proprietary nature of club member lists, we are asking that the wineries distribute an email with a link to a web-based questionnaire to all of their club members. Results should be available by late spring.

If you have any questions or thoughts about this research, please contact me at your convenience. My email address is jasterns@oregonstate.edu and the direct line to my office is 541.737.1406.

Further reading:

“What are the Attributes of Winning Wine Clubs in Napa and Sonoma?” by Liz Thach. Posted online by Wine Business.com, at https://www.winebusiness.com/news/?go=getArticle&dataid=192707

“2018 Direct-to-Consumer Wine Shipping Report” published in collaboration with SOVOS and Wines & Vines, available online at https://www.shipcompliant.com/library/

Bunch Rots in the Pacific Northwest

Dr. Jay W. Pscheidt, Professor and Extension Plant Pathology Specialist, OSU Dept. of Botany and Plant Pathology
Dr. Patty Skinkis, Associate Professor, Viticulture Extension Specialist, OSU Dept. of Horticulture

As we get into fall with a little rain, we wanted to highlight the potential for various bunch rots. These bunch rots are weather-, disease- and insect-related. Botrytis bunch rot and sour rot are the two most frequently encountered in this region, but others that are important around the world are not common here.

Botrytis Bunch Rot
We in Extension have written about the ubiquitous Botrytis bunch rot off and on over the years. Water in the form of rain or irrigation drives this disease, especially at bloom and near harvest. The fungus can infect (gain entrance to) ovaries and colonize floral tissue at bloom. It then becomes inactive (quiescent) and does not reactivate until berries begin to ripen in the fall. Open training systems and cluster zone leaf removal help create an environment that does not favor the disease. Fungicides are less effective than canopy management but are useful in wet years. Fungicide use can be challenging since sprays need to go on well before you know whether it will be a wet season, and fungicide resistance is common and complicated by fungicides used in your powdery mildew program. Read more about Botrytis bunch rot here:

Powdery Mildew
Powdery mildew is not really a bunch rot. Depending on how early infection occurs, the result may be poor fruit set or small and split berries. By the time véraison rolls around there is not much of a cluster to rot.  Small or light infections of the berry, however, can also allow Botrytis to get a foothold. Good powdery mildew control will aid Botrytis bunch rot control. 

Sour Rot
New research out of New York has defined sour rot and given us clues as to how to manage it in the vineyard. Very specifically, sour rot occurs when the berry becomes brown AND has both ethanol and acetic acid accumulation, which gives it the characteristic sour vinegar smell. The ethanol is no surprise as it comes from yeasts, but the acetic acid comes from bacteria. There is a sequence of events that is required for sour rot to occur, and it starts with wounding.

Somehow the berry skin breaks, allowing entry of these organisms. This can happen through berry growth, rainy weather during ripening (as we had a few years ago) and/or insect or bird damage. The yeasts produce ethanol that is then converted to acetic acid by the bacteria. This is still not enough to get sour rot symptoms. In New York, fruit flies were critical for sour rot symptom development. They do not need to introduce the microorganisms but are a factor all in themselves, and that factor is unknown at this time. It is unknown whether other insects, such as yellow jackets, can also induce symptoms. Targeting fruit flies with insecticides in the vineyard did result in less sour rot development. Interestingly, targeting the microbes with anti-microbial sprays alone was not effective. You can learn more by reading:

Other Grape Rots
A few other grape rots have been reported or observed in the PNW. Several more have been described in other viticultural regions of the world, including the following list. (We mention these various rots because it is always possible for new exotic organisms to be introduced into our region. They may just be a temporary “flash in the pan” problem or could establish as an annual concern over time)

  • Phomopsis: I have seen Phomopsis fruit rot only once in my 30 years here in Oregon and that was in an unmanaged vineyard used for nursery stock. A disease with similar symptoms from the southeastern USA is called bitter rot. The only way to tell the difference is by taste, which I had enough of during my postdoctoral research in New York!
  • Black rot has been reported from eastern Washington on Concord grapes but is not a common problem.
  • Anthracnose (or better named “bird’s eye rot”) and ripe rot are also fungal fruit rots more commonly found in the southeast USA.
  • White rot is a real fungal disease of grape and not someone just joking around about bird doodoo on a leaf!
  • Downy mildew: This is not a problem here but is common in many other regions of the world.

In the Winery
Grapes affected by fruit rot diseases can cause problems in the cellar as well.  Dr. James Osborne wrote this article titled, Dealing with Compromised Fruit in the Winery, for Wines & Vines magazine in August, 2014.

Bottom Line
It is most important to manage powdery mildew and Botrytis bunch rot, and to scout for fruit flies around harvest. Also, keep an eye out for unusual problems or rots. If you find some suspect diseases or unusual rots, contact your local Extension team member. We hope that the harvest will go smoothly with few problems.

Vine nutrition sampling at veraison can help you identify issues

Dr. Patty Skinkis, Viticulture Extension Specialist & Associate Professor, OSU
Dr. R. Paul Schreiner, Research Plant Physiologist, USDA-ARS

Véraison marks the start of fruit ripening in the vineyard, and it is one of the two main time points to consider evaluating vine nutrient status. Sampling petioles at bloom was the long-time standard recommendation for measuring grapevine nutrient status. However, more recently we have been suggesting that growers consider sampling vine tissues at véraison for macronutrient assessment, particularly nitrogen (N), phosphorous (P), potassium (K), and magnesium (Mg). Sampling should be conducted at approximately 50% véraison (50% color change/softening), and leaf blade or petiole samples can be taken. However, leaf blades are better for diagnosing many nutrients compared to petioles (Schreiner and Scagel 2017). Recent studies conducted in Oregon by both of our labs show that leaf blade samples at véraison serve as a good indicator of vine N status and fruit N levels (yeast assimilable N). To learn more about research into leaf and petiole nutrient guidelines and to learn about how to collect tissue samples and interpret results, see the articles listed below.

Further Reading

Schreiner RP and Scagel CF. 2017. Leaf blade versus petiole nutrient tests as predictors of nitrogen, phosphorus, and potassium status of ‘Pinot Noir’ grapevines. HortScience. 52: 174-184.
http://hortsci.ashspublications.org/content/52/1/174.abstract

Schreiner P. and Skinkis P. 2014. Monitoring grapevine nutrition. eXtension.org.
http://articles.extension.org/pages/31517/monitoring-grapevine-nutrition

Role of Auxin-Response Factor 4 (ARF4) in the Ripening Process of Grape Berry

Dr. Laurent Deluc, Associate Professor, Dept. of Horticulture, OSU Oregon Wine Research Institute

As part of the research project studying the role of the regulatory protein Auxin-Response Factor 4, namely ARF4, on the ripening initiation of grape berries, our group has lately invested time and research efforts in promoting the microvine system at OSU, which was developed by our Australian partner Dr. Mark Thomas at the Commonwealth Scientific and Industrial Research Organization (CSIRO) (Chaïb et al. 2010). In early May, we received the first plant materials from Australia (see Figure 1 & 2), which includes in vitro material from white and red-grape varieties. One question that we are often asked about the microvine system is “what is the microvine system and why is it important to research?” If recent advances in sequencing technologies and genomic tools are very helpful to build new hypotheses on complex molecular processes, such hypotheses still need to be validated in planta in order to prove the concept. When one gene from genomic data has been identified as potential link with a trait of interest (fruit quality, disease resistance, stress tolerance), one way to prove the relationship between the genetic marker and the trait of interest is to perform “genetic engineering” or molecular breeding. To do so, this approach requires the use of a reliable model system that must combine several advantages that include small space requirements for growth, short generation time (constant flowering trait), tractable system for genetic engineering (genetic transformation), and small-size genome. The microvine system offers all of these advantages.

Dr. Satyanarayana Gouthu, Research Associate in the Deluc lab, is currently visiting Dr. Mark Thomas’s lab at the CSIRO in Australia to receive the necessary training for the different steps related to microvine propagation and genetic transformation. From my interaction with Dr. Gouthu, it is clear to me that he is learning a lot about microvine, which is essential for him to “master” when he eventually initiates the genetic engineering work at OSU. Meanwhile, another aspect of his research project is also in its final phase. By the end of the summer, we hope to identify a series of potential “interactors” with ARF4. This information is necessary to understand how a protein (ARF4) is regulated and what ARF4 interacts with during the process of berry ripening? We also made significant progress in terms of adapting a new method called Atmospheric Pressure Gas Chromatography Mass Spectrometry (APGC-MS) for metabolite identification in grape berries, in collaboration with the OSU Mass Spectrometry Center. Our colleague from the center has built a database containing around 75 individual analytes belonging to different classes of metabolites (organic acids, amino acids, sugar-related compounds, and pigment- related compounds). Our goal is not only to use this database for routine metabolite analyses in our lab, but also over time to improve the depth of the database by adding new metabolites. We are currently running samples from another experiment with promising results. We are very excited using this new analytical method for our current research project on ARF4 and future research projects as well.

By using the microvine, we expect to connect the function of proteins to important traits for grapevine production. Our goal is to specifically connect the timing of ripening initiation to the protein ARF4. This information could be useful by providing the industry with a potential genetic marker associated with véraison that could serve be used to validate new practices in the field, and to identify new or existing cultivars/clones for advanced or delayed ripening more amenable to local changes in the environment due to climate change. We hope to collaborate with OWRI, OSU and other external partners in pursuit of our research objectives.

Figure 1. Microvine embryonic cells of white grape variety

 

Figure 2. Microvine plantlet of red grape variety

Literature cited:

Chaïb J, Torregrosa L, Mackenzie D, Corena P, Bouquet A, Thomas MR. 2010. The grape microvine- a model system for rapid forward and reverse genetics of grapevines. Plant J. 62(6):1083-92. doi: 10.1111/j.1365-313X.2010.04219.x

Red Blotch and Wine Quality

James Osborne, Enology Extension Specialist, OSU, Oregon Wine Research Institute

The impact of Grapevine red blotch associated virus (GRBaV, commonly referred to as red blotch) on wine quality is largely unknown, with most of the information available focused on fruit composition. A recent study on how GRBaV interferes with grape ripening at the molecular level (Blanco-Ulate et al., 2017) has been published, which may provide insights on how to mitigate the impact of the virus on fruit development in the vineyard. There are very few peer reviewed publications that have reported on winegrape compositional changes due to red blotch and most information regarding the impact on wine quality is anecdotal. A number of studies are currently being conducted in the US to determine the impact of red blotch on wine composition but results from these experiments have not yet been published. Early data from other studies suggest that the impact of red blotch is affected by site and year more than cultivar by cultivar, indicating that impact needs to be evaluated over multiple growing seasons. Based on the few published reports the two main effects on fruit quality have been:

  • A decrease in sugar accumulation leading to reduced Brix levels in grapes at harvest compared to grapes from non-infected vines. The reduction in Brix has been reported to range from 1 to as high as 5 with some varietal differences being noted (Poojari et al 2013), though in this publication the vines were co-infected with Grapevine fanleaf virus. To date the sample size is too small to make any conclusive statements about consistent differences between varietals but early reports indicate this may be the case. Other anecdotal information suggests site and season are more important than cultivar in the degree of impact GRBaV has on grape quality.
  • Lower anthocyanin concentration in grapes from red blotch infected fruit (Poojari et al 2013). Early results from studies being performed in Washington State and California also indicate lower Brix in fruit from red blotch infected vines as well as higher titratable acidity and lower anthocyanins.

While it would be expected that lower Brix will lead to wines with lower alcohol, the impact on other wine parameters such as flavor, aroma, mouthfeel, color, and sensory is relatively unknown. An upcoming presentation by Anita Oberholster (UC Davis) at the OWRI Grape Day will discuss results from some of the trials she has been conducting in California. This includes data regarding changes in wine anthocyanins and tannins as well as sensory attributes. This type of information will be vital for the development of strategies to manage this issue in the winery. If the only significant impact of GRBaV is lower Brix and higher acidity then that can be amended in the winery. However, if red blotch significantly impacts concentrations of tannins and flavor and aroma compounds then red blotch fruit will be more challenging to manage in the winery.  Sensory studies also need to be conducted to determine the specific sensory impact across different wines as well as what percentage of red blotch fruit can be used before sensory impacts become noticeable. It is likely that the percentage of red blotch fruit needed before sensory differences are noted will vary between different red wines as is seen with other taints/faults such as Brettanomyces taint where higher concentrations of volatile phenols are required in a Cab. sauvignon compared to a Pinot noir to be noticeable. We are really only at the very starting line when it comes to understanding both the specific effects of red blotch on wine quality and how these could be managed at the winery.   

Literature cited:

Blanco‐Ulate, B., Hopfer, H., Figueroa‐Balderas, R., Ye, Z., Rivero, R.M., Albacete, A., Perez-Alocea, F., Koyama, R., Anderson, M.M., Smith, R.J., Ebeler, S.E. and Cantu, D. 2017. Red blotch disease alters grape berry development and metabolism by interfering with the transcriptional and hormonal regulation of ripening. J. Exp. Bot. 68:1225-1238.  doi:10.1093/jxb/erw506

Poojari, S., Alabi, O.J., Fofanov, V.Y., and Naidu, R.A. 2016. A leafhopper-transmissible DNA virus with novel evolutionary lineage in the family Geminiviridae implicated in grapevine redleaf disease by next generation sequencing. Plos One. 8(6): e64194. doi:10.1371/journal.pone.0064194

2017 Pest Management Guide for Wine Grapes in Oregon

Now available through OSU Extension is the 2017 Pest Management Guide for Wine Grapes in Oregon. This guide is co-authored by viticulture, horticulture and pathology extension faculty at Oregon State University and updated annually. It provides chemical and cultural control information for insects, weeds, and diseases based on grapevine phenology (growth stages throughout the year). Updated information from fungicide efficacy trials is included as well as other resources and an air blast sprayer calibration worksheet.

Worker Protection Standards Regulation Changes Take Effect in January 2017

Dr. Patty Skinkis, Viticulture Extension Specialist & Associate Professor

Effective January 2, 2017, all farms, including vineyards, will require that their agricultural workers receive annual training, have easy access to information about all pesticides used on the farm, and receive necessary safety information while working around pesticides. The Worker Protection Standard (WPS), which is administered by the Environmental Protection Agency (EPA), was revised in 2015 to enhance the protections of farm workers and pesticide applicators from the risks associated with pesticides. It now requires more frequent training of agricultural workers and makes pesticide use recordkeeping a federal directive. See the employer checklist for the requirements.The revised regulations require that all farms, where agricultural plants are produced, must provide annual training of employees who work in and around pesticide application areas. This includes full, part-time or temporary employees, and it applies to areas even after pesticides are applied. Specifically, these rules apply to areas where products with “Agricultural Use Requirement” on the label are applied, which includes nearly all pesticides whether organic or not, see an example here. To determine the need and type of training to provide, see this decision guide.

It is important that you are aware of these changes, especially since it enables you as an employer to take steps in protecting workers from physical harm associated with pesticide use. If you want to do your own training of workers in-house, this will require that you have a qualified trainer which is defined as one of the following:  1) the trainer is an employee with a current ODA pesticide applicator licensed, 2) the employee completed an 8-hour Train the Trainer Course, or 3) the trainer is a third party certified trainer. Because any paid worker coming onto the farm needs to have this training BEFORE they begin work, being trained in-house may be a more convenient option for some. A number of Train the Trainer Courses are being offered by Oregon State University and may be a quicker route to being certified to train if none of your employees are ODA licensed pesticide applicators. Also, training must be done with approved WPS training materials, which are available in English and Spanish online.

All resources for the WPS  regulations and training are available online through the Pesticide Educational Resource Collaborative, including the full “How to Comply” guide. Also refer to the National Pesticide Information Center for more information about WPS and to access further resources on pesticides, their use, and training.  Please share these important updates with your colleagues and neighbors in the winegrape community.