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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.

2011 Vintage Update (30 September)

Click here for a downloadable version of this update.

**This update is a compilation of a series of emails sent between 29 and 30 Sept 2011 regarding the 2011 vintage.**

Disease Update- Botrytis Bunch Rot Alert

By Gary Grove and Michelle Moyer

First, the good news: Gerrit Hoogenboom and the AgWeatherNet team have posted a preliminary version of the Broome Botrytis Bunch Rot model on the AWN web site (http://weather.wsu.edu).  Once you are logged in, click on “AWN Models” in the vertical blue menubar and then “Grape Bunch Rot”.  Users will need to select station locations and date span (we suggest bloom through the current day) and then bloom date again.  As we are in the midst of Botrytis season there is little time for formal training so we have attached a sample model output from AWN.  The “Site Summary” output includes the bloom date (entered by client), last date of moderate to high infection risk, a choice to look at season-long conditions, and a risk index graph.  Available but not shown is also a table of some fungicides registered for bunch rot management.  Unfortunately, at this time we know little of the postinfective activity of these compounds so we cannot recommend treatment in response to an infection event; the best approach is to apply these compounds protectively BEFORE an infection event.  Given the news below, it might be a busy several days ahead.

Now the bad news: Hopefully you’ve all seen the weather forecast for the following 10 days.  The forecasts are that conditions very favorable for the development of bunch rot:

116 PM PDT WED SEP 28 2011

…COOL AND WET WEATHER NEXT WEEK FOR WASHINGTON AND OREGON…

THE WEATHER WILL BE CHANGING EARLY NEXT WEEK TO A COOLER AND WETTER
PATTERN. A SERIES OF FRONTS WILL BE MOVING ACROSS THE REGION WITH
PERIODS OF RAIN. THE FIRST SYSTEM WILL BE MOVING THROUGH ON MONDAY
WITH A STRONGER ONE TUESDAY INTO WEDNESDAY. RAINFALL AMOUNTS
THROUGH WEDNESDAY COULD BE UP TO ONE INCH AT THE LOWER
ELEVATIONS…WITH 1 TO 2 INCHES IN THE MOUNTAINS. HIGH TEMPERATURES
WILL BE IN THE 50S AND 60S WITH OVERNIGHT LOWS IN THE 30S AND 40S.
SOME SNOW IS POSSIBLE IN THE HIGHER MOUNTAINS.

We will be updating this information regularly on the WSU Viticulture and Enology Facebook page.

Best wishes and good luck!

 

Enology Notes – Grape Ripening

By Thomas Henick-Kling and Jim Harbertson

Grape flavor and acidity
The wonderful ripening weather we have had has allowed some very nice flavors to develop in most white grapes and in several reds.  It appears that we are ahead of 2010 in terms of flavor ripeness and we also have lower acidity in many vineyards.  In many white grapes the titratable acidity is already below 10 g/L and the pH above 3.0.  These are acid ranges that can very easily managed with malolactic fermentation and perhaps a small chemical deacidification – lowering final TA by perhaps 0.5 or 1 g/L.  If you see larger deacidifications needed then it is better to do this in the juice prior to fermentation.  For help with deacidification, please refer to our article last October.

Chaptalization
It seems though that acid management will not be a problem this year – or an easy one to handle.  Unfortunately our soluble solids is still lagging behind.  Yet, this is not a problem, sugar adjustments are easily made (best with neutral tasting cane sugar).  When chaptalizing, it is not a good idea (and in some cases illegal) to increase the natural alcohol content by more than 2% (v/v). Remember that 20 Brix equals 20g/100 g of liquid, or 200g/L.  To chaptalize from 20 Brix to 22 Brix you would add 20 g of sugar per liter of must.  When chaptalizing, remember to first solubilize the sugar first in must or water and allow space in your fermentation tank for the increase in volume.  A good practice is to make a 200 Brix (2000 g/L) solution and add this solution back to increase the fermentable sugar content.  At 59°F you can dissolve up to 1.97 kg of dry sugar in 1 liter of water or wine.  At 86°F you can dissolve up to 2.19 kg sugar per liter.  Remember to add the sugar under constant stirring, making sure it is all dissolved before adding the sugar solution to the must.

Botrytis bunch rot threat
Remember also that if you are going to use a fungicide that yeast are actually fungi, so following preharvest intervals are not only a legal requirement, but also a good idea for a healthy fermentation.  Clarify white musts well, as it will help to remove any spray residue.  Should you run into fermentation difficulty and you suspect spray residue as a cause, try using yeast hulls.  The yeast hulls (cell walls and membranes) bind a range of inhibitors such as fungicides (copper included).

Always remember to add yeast nutrients!  Aim for 250 mg/L Yeast Available Nitrogen.

2011 Vintage Update (23 September)

Click here for a downloadable version of this article.

By Michelle Moyer, Viticulture Extension Specialist; and Gary Grove, Plant Pathologist

Powdery Mildew, Botrytis Bunch Rot, Sour Rot

Powdery Mildew (PM): While weather conditions have remained conducive for powdery mildew control, we have passed the period of cluster susceptibility.  Mildew management should be focused on controlling canopy outbreaks if/where vegetative growth continues, keeping in mind pre-harvest intervals on some products.  For fungicide resistance management, the use of high-risk fungicides at the end of the growing season is not recommended, due to likely high prevalence of the pathogen.  (See our previous recommendations on fungicide resistance management.) Make sure you are still practicing fungicide rotation.

Botrytis Bunch Rot (BBR): As sugar accumulation advances, the likelihood of Botrytis bunch rot also increases.  Monitor weather closely, as heavy dew or precipitation events between now and harvest can result in an outbreak.  Elevate, Scala, Endura, Rovral, and Vangard are all appropriate products for véraison to harvest Botrytis control.  Copper also has limited efficacy for those practicing organic management.

Also remember, that “extended hang time” also extends the possibility of BBR infections.  Be vigilant in BBR management if you are hanging fruit on the vine longer than what is “normal” for your vineyard.

For those who are not aware, a new Extension Factsheet on Botrytis Bunch Rot has recently been published.

Sour Rot: Sour rot, called as such due to the “sour” smell of the rotting clusters (often caused by Acetobacter and other bacteria, in addition to endogenous yeasts), is differentiated from BBR by its wet appearance.  However, BBR and high levels of PM on clusters can lead to sour rot development.  Managing sour rot once it is present in the vineyard is challenging, but often compounds applied to control/prevent BBR have limited activity in managing sour rot (e.g. Rovral), especially when applied in combination with copper-based compounds.

Updates and educational blurbs are also available on the Viticulture and Enology Extension Facebook site.  The Facebook medium also provides a more interactive approach to information transfer.

Growing Degree Day Update

Warm temperatures at the end of August and in the beginning of September have caught up GDD accumulation in 2011 with that of 2010.  While still behind our historical average, the recent accumulation has been “high quality”, meaning that high temperatures haven’t exceeded the upper threshold at which vines begin to shut down, and low temperatures were not routinely dropping to temperatures that would also slow basic metabolic processes.  As a result, many people are seeing véraison, and even harvest, occurring at the same time if not earlier, compared to last year.  Reports around the valley are showing that grapes deemed for sparkling production are coming in, and the first lots for Pinot gris and Sauvignon blanc are being picked.

More information regarding specific GDD accumulation for each of the Washington AVAs is located under our Weather Data page.

 

2011 Growing Degree Day Accumulation for Yakima Valley. Temperature data is from AgWeatherNet at WSU and is sourced from the WSU-HQ weather station located at the Irrigated Agriculture Research and Extension Center in Prosser, WA.

2011 Vintage Update (2 August 2011)

Click here to download a PDF of this Update

By Michelle Moyer, Viticulture Extension Specialist, and Gary Grove, Plant Pathologist

Powdery Mildew and Botrytis Updates

Powdery Mildew (PM): We are at or nearing the end of cluster susceptibility on the East Side and forecast temperatures are also reaching highs that help to reduce powdery mildew development.  At this point, management should be focused on controlling build-up in the canopy.  For the West Side, fruit are still in a susceptible stage of development, and management practices should be focused to control cluster infections.  Forecast temperatures are still in the optimal range (65-85°F) for rapid disease development.  Please see the below paragraph concerning eradication of powdery mildew if a minor loss in control has occurred.

As discussed in the last vintage review, attempts to “clean-up” fruit is really only possibly on mild infections.  For this, an eradicant (such as a narrow-range petroleum oil at 2% rates, or potassium bicarbonate if available) combined with a protective compound is recommended. The compounds with eradicant activity are contact materials so thorough spray coverage is essential.  Fruit with severe infections will likely not recover with an eradicant spray, as significant damage has already been made to the berries, predisposing them to future rot problems. If you have a vineyard with significant levels of powdery mildew, avoid using fungicides in high-risk categories for developing resistance.  Our most resistant-prone fungicide group is the strobilurin / QoI class (Abound, Flint, Sovran, and Pristine), the use of which should be avoided if PM is already present in the vineyard.  See our previous announcement regarding appropriate use and rotation of fungicides and their resistance risks.

Effective deployment of an eradicant fungicide could require a significant increase in spray volume.  As always, spray coverage and penetration is improved when combined with the viticulture techniques of shoot thinning and fruit-zone leaf removal. However, for fruit that is developed beyond set, fruit-zone leaf removal should be approached with caution so as to avoid fruit sunburn.

Botrytis bunch rot (BBR): Forecast temperatures and precipitation for the East Side are unfavorable for BBR infections and we are nearing the end of the first infection window (flowering to bunch closure). This pre-bunch closure time is the last time that fungicide penetration into cluster interiors is possible. In addition, fruit with existing PM infections also have an increased risk of developing BBR after véraison, due to microscopic damages PM has made to the developing berries.  Due to the increased likelihood of a delayed harvest, keep latent Botrytis infections in-check now to avoid more significant problems post-véraison.   If you DO NOT (look closely) have PM  in your vineyard, those choices for control include Flint , Pristine, Inspire Super, and Adament at highest labeled rates or tank mixes of Quintec, Procure, Rally, Elite,  and others with Elevate, Scala, Vangard, or Rovral.    If PM is present in the vineyard and BBR is a concern, a good choice at this point would be a tank mix of an eradicant and Inspire Super.  The ingredients in Inspire Super (difenconazole + cyprodinil) provide forward protection against both diseases and oil or potassium bicarbonate deal with the PM that may already be present.

West Side growers are still in a critical development stage for controlling BBR.  Mild temperatures, heavy dew, and high humidity all favor infection.  A dual purpose fungicides such as Inspire Super, Adament, and Pristine will provide protection against both PM and BBR if applied at this stage at the highest rates.  However, avoid the use of Adament or Pristine if PM is already present, as they have a strobilurin component (see precautions above).

Updates and educational blurbs are also available on the Viticulture and Enology Facebook site.  The Facebook medium also provides a more interactive approach to information transfer (www.facebook.com/WSU.Vit.Enol.Ext).

Growing Degree Day Update

The vintage is still holding steady- and behind- last year, with WSU-HQ 172 GDD (approximately 8 days) behind 2010, and 393 GDD (approximately 18 days) behind the long-term average.  Forecast temperatures for the East Side indicate an average daily accumulation of 23 GDD for the next 10 days, and an average daily accumulation of 13 GDD for the West Side. Below is the Growing Degree Day (GDD) chart for the Yakima Valley AVA (WSU-HQ at IAREC), highlighting this year, the long term average, and two representative warm (2003) and cool (2010) years.  Click here for more information regarding specific GDD accumulation for each of the Washington AVAs.

Figure 1- 2011 Growing Degree Day Accumulation for Yakima Valley. Temperature data is from AgWeatherNet at WSU and is sourced from the WSU-HQ weather station located at the Irrigated Agriculture Research and Extension Center in Prosser, WA.

 

2011 Vintage Update (July 19)

To download a PDF of this article, click here.

By Drs. Michelle Moyer and Gary Grove

Powdery Mildew and Botrytis Bunch Rot Updates

Powdery Mildew (PM): Reports have been rolling in from around the state concerning emerging levels of powdery mildew on fruit clusters. The disease symptoms many are seeing now are a result of infections that happened 10+ days ago (perhaps as long as 21 days ago).  This season’s generally mild temperatures (highs in the 80’s, lows in the 50-60’s F), along with moderate humidity and cloudy conditions have created perfect conditions for powdery mildew infection and development.  If you are seeing disease symptoms now, check your spray records for indications of exaggerated spray intervals earlier in the season (and take note for next year) or application at rates lower than specified on the product label.  Slow pre-flowering development kept elongating clusters exposed in a state of susceptibility and extended spray intervals due to cool weather likely created gaps in disease management.

To clean up mildly infected fruit, an eradicant (such as an narrow-range petroleum oil or potassium bicarbonate) combined with a protectant is recommended. The compounds with eradicant activity are contact materials so thorough spray coverage is absolutely essential.  Fruit with severe infections will likely not recover with an eradicant spray, as significant damage has already been made to the grapes, predisposing them to future rot problems. Be vigilant with your spray program.  Make sure you are using proper rates, are getting good coverage, and making applications at appropriate intervals.  Spray coverage and penetration is improved when combined with the viticulture techniques of shoot thinning and fruit-zone leaf removal.  If you have a vineyard with significant levels of powdery mildew, avoid using fungicides that are in the high-risk categories for developing resistance.  Our most resistant-prone fungicide group is the strobilurin / QoI class (Abound, Flint, Sovran, and Pristine).See our previous announcement regarding appropriate fungicides and their resistance risks.

Botrytis bunch rot (BBR): We are also still in a critical period Botrytis infection (bloom to bunch closure).  Those fruit with existing PM infections also have an increased risk of developing BBR after véraison, due to microscopic damages powdery mildew has made to the developing berries.  Due to the increased likelihood of a delayed harvest, keep latent Botrytis infections in-check now to avoid more significant problems post-véraison.  See our previous announcement regarding BBR management.

With potential for showers during the next several days, and because we are nearing bunch closure (the last opportunity to get fungicide to the inner portions of clusters), using a fungicide with activity against BBR should be considered.  A dual purpose fungicide (activity against PM and BBR) such as Inspire Super, Adament, and Pristine will provide protection against both diseases if applied at this stage.  However, avoid the use of Adament or Pristine if mildew is already present, as they have a strobilurin component (see precautions above)

Disease Alerts: For those who are not aware, AgAlertz will send disease warnings directly to your phone or email.  It is powered by WSU’s AgWeatherNet.  There are representative sites in most of the AVA’s, and the daily update of the relative risk of powdery mildew infection is invaluable.  Though still in Beta form (forecast data has not been integrated yet), it will likely become a staple in your “Inbox”.

We (Gary and I) also do updates and educational blurbs on the WSU Viticulture and Enology Extension Facebook site.  For those with smartphones or regular internet access, this might be a good media choice to be connected to in order to receive timely updates.


Growing Degree Day Update

The vintage is still holding steady- and behind- last year.  Vines are generally through set on the East side, nearing bunch closure in some areas.  Vines are into bloom on the West side.  Below is the Growing Degree Day (GDD) chart for the Yakima Valley AVA (WSU-HQ at IAREC), highlighting this year, the long term average, and two representative warm (2003) and cool (2010) years.  Click here for more information regarding specific GDD accumulation for each of the Washington AVAs.

Figure 1- 2011 Growing Degree Day Accumulation for Yakima Valley. Temperature data is from AgWeatherNet at WSU and is sourced from the WSU-HQ weather station located at the Irrigated Agriculture Research and Extension Center in Prosser, WA.

 

2011 Vintage Update (5 July)

 Click here for a downloadable version of this update

By Michelle Moyer, Viticulture Extension Specialist

By many accounts, 2011 has been a challenging year across the state. Patchy, yet severe, cold damage from the “Thanksgiving Freeze” in 2010 has many vineyards starting over, or at significantly reduced yields due to loss of the primary fruiting buds. This was followed by late-spring frost damage in some sites at the end of May.  Finally, 2011 is lagging in growing degree day (GDD) accumulation (Table 1). Across the region, we are ranging 243 to 369 GDD units behind 2003, which was considered a warm year. We are ranging 35 to 128 GDD units behind 2010, which was considered a cool year.

Table 1:  Growing Degree Day accumulation (base 50°F) from April 1 to July 4, for 2011, 2003 (warm year) and 2010 (cool year).  All data was accessed from AgWeatherNet (AWN) (www.weather.wsu.edu).
AVA: Station 2011
2003“Warm Year” 2010“Cool Year”
Puget Sound- Mt. Vernon  345  588 380
 Rattlesnake Hills: Outlook  609  963  717
 Yakima Valley: WSU-HQ  612  896  678
Lake Chelan: Chelan South  613  n/a  701
Walla Walla Valley: Walla Walla  628  918  689
Snipes Mountain: Port of Sunnyside  629  930  723
Columbia Gorge: Mary Hill  641  n/a  719
 Wahluke Slope: Mattawa  708  1072  803
Red Mountain: Benton City  730  1099  822
 Horse Heaven Hills: Paterson  768  1052  866

 

Bloom is slowly coming to an end in Eastern Washington, for both juice and wine grapes. As a historical reference, the average first bloom for Concord is June 1, indicating we are about 3-4 weeks behind “schedule” in most areas.

However, this means very little when speculating on fruit quality and when it will ripen. If you look closely at GDD in Fig. 1, the warm 2003 and cool 2010 growing seasons started similarly, but had drastically different endings. A warm spell in May initially separated the accumulation curves, but the really difference came in mid-July. It truly is the temperatures in July, August and September that can determine a vintage. It is too early to predict how and when grapes will ripen, as we cannot predict with sufficient accuracy how the weather will progress in these critical months.

If we compare 2011 to 2003 and 2010, we can calculate a “best” and “worst”-case scenario. From July 4 to Sept 15, 2003 accumulated 1653 GDD, totaling 2549 GDD; 2010 accumulated 1359 GDD, totaling 2037 GDD. If the current season accumulated the same GDD as in 2003 or 2010, it would place us at 2265 GDD and 1971 GDD by Sept 15, respectfully. In an “average” year, we would accumulate 1395 GDD (based on data from 1924-2010), which would place us at 2007 GDD for 2011. With an average daily accumulation of 14 GDD in September, we could be (at Sept 15) approximately 16 days ahead of 2010 if we have the best-case scenario of warm temperatures, 5 days behind of 2010 if we have the worst-case scenario of cool temperatures, and 2 days behind 2010 if we have “average” temperatures. These forecasts were based on data from WSU-HQ only.

Figure 1- Accumulated growing degree days for the Yakima Valley AVA (WSU-HQ) for comparison reference. Graph updates are available at: www.wine.wsu.edu/research-extension/weather/growing-degree-days/

 

Conclusion thus far: Should temperatures stay cool, the vintage may be delayed compared to last year. Even with a delay, we will have enough time to ripen fruit, as climate conditions in Eastern Washington are conducive to reach sufficient sugar content without the presence of unripe flavors. However, with cool vintages, this ripeness may not correspond to traditional harvest parameters vintners in the area are accustom to, it therefore is important to harvest based on flavor development, not numbers. If cool temperatures persist, winemakers may have to adjust their practices as in 2010 to work with fruit that has more acidity (more malic acid) and lower pH. In 2010, these adjustments were often made by using malolactic fermentation (even in some wines were it was not typically used) and by doing small chemical deacidifications in the must and/or the wine. Information on chemical deacidification and malolactic fermentation is available at http://wine.wsu.edu/research-extension under “Articles”. More information on MLF workshops on July 12 and 14 is also available on the website.

Article was prepared with enological input from Dr. Thomas Henick-Kling, Director of Viticulture and Enology, WSU-TriCities.

Click here to access WSU’s Growing Degree Day page for Viticulture

 

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 www.wine.wsu.edu/research-extension.

 


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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