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Grapevine Cold Hardiness Model Now Available for all AgWeatherNet Stations

**For a downloadable version of this article, please click here**

By Michelle Moyer, WSU Viticulture Extension Specialist

Just in time for the cold weather, the WSU Viticulture Research Team, lead by Dr. Markus Keller, in collaboration with AgWeatherNet directed by Dr. Gerrit Hoogenboom will be releasing a Grapevine Cold Hardiness Model for all available AgWeatherNet weather stations throughout Washington.

This model is based on simulations** of how grapevines respond to cold temperature throughout the winter. It provides the estimated critical low temperature thresholds for bud damage of over 20 wine and juice grape cultivars based on the locally observed temperature for each weather station.  These thresholds represent temperatures that would kill 10%, 50%, and 90% of the primary buds for each particular cultivar. The model also predicts how the cold hardiness of the selected cultivar is changing in response to local temperatures as the dormant season progresses. If a temperature threshold has been reached, a warning statement indicating the level of damage is provided.

In addition, the Grape Cold Hardiness Model page has direct links to information regarding Assessing and Managing Cold Damage in Washington Vineyards, a new WSU Viticulture and Enology Extension publication.

Official launch of the model will be December 1, 2011. It is available on the Grape Cold Hardiness Model page on AgWeatherNet.  In order to access the model, you must be a registered user of AgWeatherNet. Registration is free.

This model is the result of recently published research efforts by Ferguson et al. (2011) in Annals of Botany, titled “Dynamic thermal time model of cold hardiness for dormant grapevine buds.”

With partial funding from the Washington Association of Wine Grape Growers, the WSU Viticulture Research Team will continue to monitor cold hardiness levels for up to 20 grape cultivars at WSU-IAREC in Prosser, WA.  These real-time observations can be found on the WSU Viticulture and Enology Extension Website Cold Hardiness page.  This site also contains valuable information regarding preventing, assessing and responding to cold damage in vineyards.


**Note of caution: As with all models, there is an associated error with the temperature threshold estimate. While the warning statements may not indicate bud damage, if actual temperatures reached levels near the threshold level, damage may still have occurred.  Conversely, if the threshold temperature was met, this does not necessarily mean widespread bud damage.  Careful vineyard assessment after a suspect cold event is still a necessary part of management.

Note to Cold Soak

By Thomas Henick-Kling Professor of Enology

A note of precaution to using cold soak

The recent rains and earlier powdery mildew infections have caused damage to some grapes, the grape surface is punctured, microorganisms have entered the interior of the berries. For this to occur, we do not need clearly visible mold infection, even some slight growth of fungal hyphae in the surface layers of the berry is sufficient to open it up to spoilage yeast and bacteria. Studies at Cornell University have shown us that such damage by powdery mildew (and following Botrytis) will bring grapes that have a much higher load of yeast and bacteria than healthy undamaged fruit. The damaged fruit can have more than several million yeast per milliliter of juice compared to healthy fruit which has several hundred or at most several thousand yeast per milliliter. In addition, these yeast are not the friendly wine yeast, Saccharomyces cerevisiae, instead, they are mostly Kloeckera sp (Hanseniaspora sp), Pichia sp, and Candida sp yeasts that can produce large amounts of acetic acid and acetic acid esters. Especially Kloeckera sp yeasts can survive and grow during fermentation, even dominate some wine fermentations. This of course can cause major flavor defects.

Cold soak is very risky with such damaged fruit. Inspect the fruit carefully.

What you can do to minimize your risk when using cold soak

Use SO2 (30 to 50 PPM depending on pH) to help suppress growth of unwanted yeast and bacteria. At 50 to 60°F, Kloeckera yeasts are quite comfortable and grow faster than Saccharomyces yeasts. Therefore, if you use cold soak with white or red grapes, make sure the must is truly cold, i.e. Below 10°C or 50°F. Also, after the cold soak period warm the must quickly to 65 to 68°F to encourage the growth of Saccharomyces yeasts.

To assure the dominance of Saccharomcyes yeasts, it is best inoculate with a yeast
starter culture.

If you choose cold soak, you can add a yeast starter culture to the must immediately after you crush the grapes. Make sure that the starter culture is carefully adapted to the low temperature of the must: lower the temperature of the starter culture slowly so the yeast are not temperature shocked and stay highly viable! This addition of a yeast starter culture at the beginning of the cold soak helps suppress the growth of unwanted yeast and bacteria. Again, at the end of the cold soak period, warm the must quickly to 65 to 68 degrees F to favor the growth of Saccharomyces and start the alcohol fermentation.

New Fungicides for Grapevine Powdery Mildew Management (2011)

Click here for a downloadable version of this article

By Gary G. Grove and Mark E. Nelson

WSU-IAREC, Prosser, WA

As of spring 2011 grape growers in Eastern Washington have several new fungicides at their disposal for managing powdery mildew on wine grapes. Notice of these registrations was not received in time for inclusion in the WSU 2011 Pest Management Guide for Grapes in Eastern Washington. New products included in the powdery mildew toolbox include Adament (tebuconazole + trifloxystrobin), Inspire Super (difenoconazole + cyprodinil), Unicorn (tebuconazole + sulfur) and Vivando (metrafenone). Adament and Inpsire Super, along with the existing products Flint (trifloxystrobin) and Pristine (pyraclostrobin + boscalid), provide the added benefit of (when applied at proper rates) also controlling Botrytis bunch rot. The full component of powdery mildew compounds is presented in Table 1. The table includes fungicide class information, and Fungicide Resistance Action Committee (FRAC) group number or code. The FRAC code represents the mode of action of the fungicide. This information is helpful when designing a fungicide program that conforms to FRAC resistance management guidelines. It is important to remember that if a pathogen population develops resistance to fungicides within a FRAC group, it is likely to be resistant to all members of that group. Resistance is more likely to develop if the pathogen is frequently treated with one or multiple fungicides within a given FRAC group. Included in the table are members of the fungicide classes (or FRAC Groups) known as benzophenones (metrafenone, Group U8), DMI (demethylation inhibitors, Group 3), QoI (quinone outside inhibitors; previously called strobilurins, Group 11), quinolines (quinoxyfen, Group 13), sulfur (Group M2), various “biological” fungicides (Group 44), petroleum derived spray oils, and potassium bicarbonate. Petroleum spray oils and potassium bicarbonate are listed as “Not Classified” (NC) by FRAC. Several products are formulations or “premixes” of two different fungicide classes, modes of action, of FRAC groups. Consult product labels for appropriate rates and spray intervals. The resistance risk is product-dependent (Table 1). All of the aforementioned “new” products have performed well in efficacy trials at WSU-IAREC.

The availability of “premix” or combination fungicide formulations is a relatively recent trend in agriculture. The grape toolbox contains several of these product types: Adament (tebuconazole + trifloxystrobin), Inspire Super (difenoconazole + cyprodinil), Pristine (pyraclostrobin + boscalid), and Unicorn (tebuconazole + sulfur). Both active ingredients in these compounds, with the exception of Inspire Super, have activity against powdery mildew (only the tebuconazole component of Inspire Super is active against the disease). When both modes of action have activity against the target organism, some level of resistance management is built into the products provided that they are used rationally. The use of “premix” types of products can provide better disease control, provide disease control security if there is field resistance to one of the two active ingredients, and help prevent resistance if there is not.

A recent survey revealed that QoI (Group 11) or QoI-containing fungicide products (Abound, Flint, Pristine, and Sovran) were the industry’s first line of defense against powdery mildew. The resistance risk of these Group 11 fungicides (formerly known as strobilurins) is high while the risk of other important classes (DMI, quinolones, and benzophenones) is considered medium. The resistance risk of contact fungicides sulfur, narrow range petroleum oil, and potassium bicarbonate is low. We have no evidence of fungicide resistant mildew populations in Eastern Washington but this could change rapidly given the nature of powdery mildew and the resistance history (in grapes) of Group 11 and Group 3 fungicides. Therefore it is imperative that resistance management guidelines be followed beginning with the introduction of the group.

General resistance management guidelines include the incorporation of cultural practices that lower disease pressure. Cultural practices such as vigor management, shoot removal and positioning, and leaf removal lower disease pressure and improve spray penetration. The incorporation of these practices serves to lower selection pressure on pathogen populations. Always use fungicides in a protective, rather than reactive, manner: It is far easier to prevent powdery mildew than to cure it. Additional guidelines include limiting the number of applications of individual modes of action per season and limiting sequential applications. Do not tank mix or alternate fungicides with the same FRAC number in a spray program. Medium risk compounds such as DMI (Group 3) and quinoline compounds (Group 13) should be applied no more than 3 times per season and no more than twice in sequence. High risk QoI (FRAC Group 11) compounds or premixed formulations containing them (Adament, Flint, Sovran, Pristine, and Abound) fungicides should be preferably alternated 1:1 with other modes of action or Groups. It is preferable to make only one application of any resistance-prone compound and then switch to a fungicide from a different class or FRAC group, but the cost of this approach can be expensive in Eastern Washington. Never exceed more than two QoI applications in sequence. If two sequential applications of a QoI fungicide are made, this “block” should be alternated with at least two applications of one or more fungicides of a different mode of action or FRAC group. When QoI compounds are used as a solo product (Abound, Flint, and Sovran), the number of applications should be no greater than 1/3 of the total number of fungicide applications per season. In programs utilizing tank mixes or pre-mixes of a Group 11 fungicide with a fungicide of another group (e.g. Adament or Pristine), the number of Group 11 fungicide (QoI)-containing applications should be no more than 1/2 of the total number of fungicide applications per season. It also helps to tank-mix fungicides from different groups that are both effective against powdery mildew. Sulfur is a relatively inexpensive and effective companion product for mixing with medium- or high-risk compounds. Try to include it in every spray tank aimed at powdery mildew if permitted according to usage instructions on product labels. Always follow label instructions pertaining to application rates and intervals and always use a properly calibrated sprayer and sufficient spray volume to provide good coverage.

The most critical period for powdery mildew control is from immediate prebloom to three weeks postbloom. Our most effective compounds should be utilized during this period. Bloom is also a critical period for the establishment of Botrytis bunch rot in the vineyard. As noted above, several of our highly effective powdery mildew fungicides/fungicide premixes (Adament, Flint, Inspire Super, and Pristine) provide (when used at appropriate rates) activity against both powdery mildew and bunch rot. These compounds are logical for deployment during bloom but remember to keep applications of QoI (Group 11) compounds or mixtures containing them to a minimum.

Table 1: Fungicide choices for powdery mildew management in Washington Wine grapes for 2011.
Trade Names1 Active Ingredients Class FRAC Group2 Resistance Risk
Abound azoxystrobin QoI 11 High
Adament tebuconazoletrifoxystrobin DMIQoI 311 MediumHigh
Amicarb potassium bicarbonate Carbonate NC Low
Flint trifloxystrobin QoI 11 High
Inspire Super difenoconazolecyprodinil DMIAP 39 MediumMedium
JMS Stylet Oil narrow-range petroleum oil PDSO NC Low
Kaligreen potassium bicarbonate Carbonate NC Low
Pristine pyraclostrobinboscalid QoICarboxamide 117 HighMedium
Rally myclobutanil DMI 3 Medium
Regalia extract of  Reynoutria sachalinensis Plant host inducer P Low
Serenade MAX Bascillus subtilis Biological 44 Low
Sonata Bascillus pumilis Biological 44 Low
Quintec quinoxyfen Quinoline 13 Medium
Rubigan3 fenarimol3 DMI 3 Medium
Sovran kresoxim-methyl QoI 11 High
Sulfur4 sulfur sulfur M2 Low
Unicorn tebuxonazolesulfur DMIsulfur 3M2 MediumLow
Vivando metrafenone benzophenone U8 Medium
1 Trade names in bold/italic are new to the industry in 2011
2 Fungicide Resistance Action Committee
3 Active ingredient (fenarimol) available under different trade names (e.g. Focus and Vintage)
4 Various formulations may be available

Use pesticides with care. Apply them only to plants, animals, or sites listed on the labels. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.

YOU ARE REQUIRED BY LAW TO FOLLOW THE LABEL. It is a legal document. Always read the label before using any pesticide. You, the grower, are responsible for safe pesticide use. Trade (brand) names are provided for your reference only. No discrimination is intended, and other pesticides with the same active ingredient may be suitable. No endorsement is implied.

Managing Botrytis Bunch Rot in 2011

To download this article in PDF form, click here

By Drs. Michelle Moyer and Gary Grove, WSU-Prosser

Please note: Much of this information will be available, in an expanded format, in the Spring 2011 issue of the Viticulture and Enology Extension News, available in April 2011. 

Bunch Rot BBR is a disease of sporadic occurrence in Eastern Washington’s normally arid climate.  However, unseasonably moist weather during May-June and again in September 2010 resulted in a severe epidemic of BBR. Climates with higher annual rainfall, and cooler conditions during bloom and harvest, such as those in Western Washington, are prone to annual outbreaks of BBR.

BBR can infect fruit at two different stages: from bloom to bunch closure, and again from véraison to harvest.  BBR is favored by cool, moist conditions. During the first stage, BBR infects clusters through cap scars, dying stamens, and survives on floral and other debris that gets stuck inside the cluster during closure.  These infections remain latent (inactive) until véraison, where they can then express classic BBR symptoms.   At the end of the season, BBR can infect ripening fruit through wounds, often caused by insect feeding, powdery mildew damage, or berry splitting as a result of compact cluster architecture.

If we fall into our general summer weather patterns, there is the possibility of over spraying for BBR as a reaction to what happened last year.  To avoid this, WSU in collaboration with WAWGG, held a grape disease workshop in January to help develop a rational strategy for managing BBR in 2011.  Drs. Doug Gubler (UC-Davis) and Wayne Wilcox (Cornell University) shared their extensive experiences with BBR management in California and New York, respectively.  Washington growers recognize the bloom to pea-sized berry period as the keystone for managing powdery mildew (PM) on fruit, and typically make 2-3 PM fungicide applications during this period to control it.  Like PM management, the bloom period is critical for BBR control.  The use of fungicides that offer control of both is recommended during bloom to control PM and to prevent the infection of flower parts by BBR (Table 1).

Timing Compound Powdery Mildew Botrytis Notes
Bloom to Fruit Set   Trifloxystrobin (Flint)  Yes  Yes  Apply at highest labeled rates for dual control.
 Pyracostrobin + boscalid  (Pristine)  Yes  Yes
  Difenconazole + cyprodinil (Inspire Super)  Yes  Yes  Read label for appropriate rates.
 Bunch Closure  Trifloxystrobin (Flint)  Yes  Yes  Apply at highest labeled rates for dual control if wet weather conditions
  Pyracostrobin + boscalid  (Pristine)  Yes  Yes
   Difenconazole + cyprodinil (Inspire Super)  Yes  Yes   Read label for appropriate rates.
 Véraison to Harvest  Elevate (fenhexamid)  No Yes
 Scala (pyramethanail)  No  Yes
 Rovral (iprodione)  No  Yes
 Vangard (cyprodinil)  No  Yes


Drs. Gubler and Wilcox also recommended taking notes on prevailing and predicted weather conditions when devising BBR management strategies. If the 2011 season has above-average precipitation, additional dual-purpose fungicide applications should be considered at pre-bunch closure, while BBR specific compounds should be applied at véraison and preharvest (Table 1). It is imperative to realize that during years with “normal” precipitation (e.g. DRY between fruit set and harvest), véraison to preharvest fungicide applications for BBR may be unnecessary.

The role of leaf removal in managing both PM and BBR cannot be overemphasized.  Both Drs. Gubler and Wilcox stressed the incorporation of this cultural practice into the overall vineyard disease management system.  Dr. Gubler presented data indicating that leaf removal is equally or more important than fungicide applications for managing BBR.  Leaf removal also improved management of PM.  Much of this improved management of disease is through better spray penetration into the fruit zone, and increased air circulation and sunlight penetration, which reduces the environmental favorability for BBR and PM infection of fruit.

Last year also presented challenges in controlling PM, though not to the same extent as BBR.  Targeting PM fungicides from bloom to set is the key to controlling disease development on fruit.  What many people don’t realize is that control of PM is also a key component of controlling BBR.  Severe PM infections can result in fruit cracking, a clear entryway for BBR.  However, light PM infections (referred to as “diffuse infections”), which can occur on fruit near the end of pea-size development, can also lead to substantial BBR.  Diffuse infections create tiny damages in the grape berry skin, which are only visible with a hand lens or microscope, and are avenues for BBR infection.

More information on fungicide options for WA growers and how to develop a spray program are available in the 2011 WA State Grape Pest Management Guide, downloadable from


Use pesticides with care. Apply them only to plants, animals, or sites listed on the labels. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.

YOU ARE REQUIRED BY LAW TO FOLLOW THE LABEL. It is a legal document. Always read the label before using any pesticide. You, the grower, are responsible for safe pesticide use. Trade (brand) names are provided for your reference only. No discrimination is intended, and other pesticides with the same active ingredient may be suitable. No endorsement is implied.

March 2011- I have cold-damaged buds. How should I adjust my pruning?

In response to the wide-spread bud damage we’ve seen this year (learn how to spot it with “Assessing Cold Damage in Grapes“) as a result of cold temperatures, we’ve created a quick cheatsheet to help calculate the number of buds you should leave while pruning.  Learn more»

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