Whitewater Hill Weather Related Info

  • Winery Temperature Log
  • 31 Road Weather Forecast (NWS) (text)
  • Kay Vineyard Weather Forecast (NWS) (text)
  • RMAVV Weather Stations (login: guest/guest)
  • Current conditions at Walker Field
  • Cold Injury

    Low temperatures during Colorado winters can cause damage to grapevine tissues and buds. Winters in Colorado are similar to those in Washington State and growers there are faced with similar problems. Washington State University periodically tests grapevine tissues and buds for cold injury tolerance. Colorado currently does not have as comprehensive a program, so growers here must guess the cold injury tolerance in their own vineyards. One way to guess is to look at the Washington State University statistics and then try to extrapolate the results to Colorado. However, due to the difference in latitude and solar radiation and therefore longer wintertime daylength and greater soil warming by the sun in Colorado, vines in Colorado make take longer to achieve dormancy, making them more susceptible to cold temperatures in the fall than in Washington.

    Another way to guess the cold injury tolerance is to use a model. The following link uses a model based on temperature input at the 31 Road vineyard to guess the cold injury tolerance. It looks at air temperature history and calculates the cold injury temperature. It attempts to match the cold hardiness curve as if samples were taken daily and subjected to freezer tests. The model is based on empirical analysis of Colorado temperatures since 1996 and noting where the suspected cold injury events occur. The model is tuned to output cold injury events that match these past suspected cold injury events (see table).

    The following table shows the cold injury events since 1996. Only 1997, 2000, and 2003 could be considered years without cold injury. This table was compiled largely with data from our own vineyards and probably understates the actual damage to most other vineyard acreage in Colorado. For example, the West Elks region had nearly 100% damage in 2007.

    These frequent cold injury events should give pause to anyone considering planting vinifera grapes in colorado, as loss of crop and retraining expenses virtually guarantee an unprofitable venture. Only the Palisade area east of the Colorado river can be considered reliable for grape growing. However, peaches are more suitable, producing a larger crop and better return. Some vineyard land is currently being converted back to peaches. Marginal vineyard land is being returned back to pasture. Many small grape growers have leased their vineyards with no hope of any return to larger growers solely to keep the land maintained.

    Harvest Year Estimated Crop Loss (%) Description
    1998 10% Chardonnay vine-splitting. Record peach crop.
    1999 40% Peach crop unaffected by winter, but down by 20% due to spring frosts.
    2001 10% Young vines knocked down, vine-splitting on older vines. Cabernet Franc and Cabernet Sauvignon about 20% knocked down, Chardonnay about 10%, bud damage on Merlot
    2002 30% Winter injury was more severe than 2001, knocking down young vines and causing some vine splitting among older vines. Hardest hit were Cabernet Franc, Chardonnay and to a much lesser extent Cabernet Sauvignon and Merlot.
    2004 20% Merlot buds were 80-100% dead and the Cabernet Sauvignon buds were 80% dead. Significant cane damage as well in Syrah and Cabernet Franc.
    2005 20% Merlot buds were 50% dead at 32 RD and 65% at Kay Family Vineyard. Other varieties were affected to a lesser extent. By adjusting pruning were able to get a decent crop, so yields were about the same as better years.
    2006 5% Cabernet Sauvignon in cold spots knocked down
    2007 50% Spring frosts caused bud damage primarily on Merlot and Chardonnay. Cane damage was likely fall event, although January event is another possibility. Only Riesling survived unscathed. Peach crop unaffected by winter but down slightly due to spring frosts.
    2008 20% Cane damage on Cabernet Sauvignon, Syrah, Cab Franc and Chardonnay. Merlot to a lesser extent.
    2009 20% Extensive cane and bud damage on Merlot. Some cane damage on most varieties, including Riesling, although Syrah did well in our vineyard, but poorly at some other locations. All vines pushed very slowly and erratically.
    2010 75% All trunks on all varieties at Kay Vineyard destroyed. At 31 and 32 road, Cabernet Sauvignon, Cabernet Franc and Syrah had 99% bud damage but still produced crop. Chardonnay survived the winter but was frosted in spring and produced no crop. Riesling had the least bud damage (20%) and the most crop.
    2011 75% New years eve and day temperature of -9 degrees after warm December caused significant damage, destroying most primaries. Secondaries swelled in April but were destroyed by hard frosts of 26 degrees in late April and early May, except for late-budding Cabernet Sauvigon. All varieties had some crop from tertiaries. Riesling and Cabernet Sauvignon performed the best, although barely ripe when harvested due to the cold spring.
    2012 50% One of the warmest winters on record, yet Riesling and Viognier didn't survive at Kay Vineyard, perhaps due to a mild cold event in spring after sap was already rising. One of the latest hard frosts on record (Memorial Day) killed all the trunks of the remaining varieties, with the canopy out almost two feet. Note that the leaves were not frosted, but the trunks were killed at ground level, demonstrating how important it is to monitor temperatures near the ground and run wind machines based on ground temperature. One of the hottest summers on record made irrigation more challenging, resulting in reduced crop.

    Once the grape buds enter first swell in spring, the cold injury temperature must be based on a visual inspection of the variety.

    In April of 1997 Washington ran some freezing tests on grape buds and canes at different phenological stages and found the following:

    • Cabernet Sauvignon at first swell sustained no damage down to 25 F.
    • Merlot at full swell showed slight damage to the buds, phloem, and xylem at 25 F. More serious damage to the phloem and xylem occurred at 23 F.
    • Chardonnay at bud break showed slight damage to the buds and phloem at 27 F. More serious phloem and xylem damage occurred at 25 F. Buds were seriously affected at 24 F.
    • Interlaken at first leaf stage sustained cane damage at 28 F and leaf damage at 26 F. Both cane and leaf damage became serious at 25.

    Our experience at Whitewater Hill substantiates this approximate temperature range. On April 11 2007, we experienced temperatures as low as 26.6 degrees during bud swell of Merlot and Chardonnay with resulting bud damage, but no damage to Cabernet Sauvignon or Riesling. Our general recommendation is to launch mitigation measures when the temperature reaches 28 degrees or below after bud swell.

    This is true even with the practice of late pruning. Our experience shows that even buds not swollen on a cane with swollen buds are susceptible to these low temperatures. While late pruning can protect green tissue, it apparently does little to protect buds during bud swell.

    Wind Machine Project

    Cold injury countermeasures such as wind machines have proven cost-effective in reducing crop loss in peach orchards and vineyards in Colorado. While peach orchards employ countermeasures during the spring frost season, the table above indicates that the most damaging events to vineyards normally occur during the late fall and winter.

    Orchards and vineyards east of the town of Palisade are successful largely to the canyon wind that effectively mixes warm air with cold and results in moderate temperatures. (The area also benefits from radiation from the canyon walls, although this can be a mixed blessing if it causes vines to deacclimate during late winter). Further down valley, these winds quickly disperse and become negligible.

    We have recently installed wind machines at each of our vineyard locations and are starting to learn how to use them effectively. On the cold injury event of November 29-30, 2006, we ran the machine at our coldest location and were able to keep the temperature above that recorded in the protected area east of Palisade. However, we failed to run the machine during successive cold injury events that winter and had almost total crop loss at that location. We have had other maintenance, management and staffing issues that have prevented early success with the machines.

    The science of winter dieback and protection measures is also only beginning to become clear. The trunk injury that we suspect may be occuring very low on the trunk, perhaps inches above the ground. The wind machines may be ineffective in their ability to cause air movement this low on the ground. Hilling or other vine trunk protection may be necessary before the onset of cold temperatures in order to effectively use the wind machines.

    Part of the difficulty in running the machines is that it is a very long cold season. The machines, process and staffing need to be in place between the middle of September and the middle of May. The cold injury event can occur at any time and can easily occur while the operator is out of town or sick. The entire process needs to be tested frequently in order to be ready for an unexpected cold injury event.

    Accelerating Cold Acclimation

    Raising temperatures artificially through the use of wind machines is one way to reduce winter injury. Another way is to attempt to accelerate the vines natural process of cold acclimation. Anecdotal evidence suggests that placing mild stress on the grapevine (or other woody perennials) by the reduction of irrigation water in fall may accelerate the process of cold acclimation. Our policy is to irrigate heavily in August and up to September 5, then withhold irrigation water until October 15 and then refill the soil profile. The lack of irrigation water during this period may induce a mild vine stress that results in earlier cold hardiness which may protect from early fall freezes. It may also reduce tissue water content which might also lower the temperature of injury. The vine stress probably has no effect on mid winter cold hardiness. Indeed, we are unsure whether it has any effect at all. Refilling the soil profile in late fall may aid in preventing winter dessication or preventing the freezing of roots, although it it difficult to know whether the practice has any cultural effect.

    What we are really searching for is a magical elixir that can be sprayed on or soil applied that would cause the vine to achieve its maximum cold hardiness in a very short time. As yet we have not discovered it.

    Cold-hardy Grape Cultivars

    Recent availability of high quality cold hardy grapevine cultivars may be the ultimate answer to Colorado's grape growing industry. Grapes with mixed parentage of vinifera and endemic American varieties can perform better during cold injury events because the parent American varieties are acclimated to cold temperatures. They also tend to be more resistent to fungal diseases and can be grown without the application of antifungal sprays. For this reason, they can be an ecologically superior choice to vinifera.

    We have trialed Chambourcin and it has performed well from 2001 to 2010, surviving all cold injury events and producing fruit each year. In 2012 we replaced two acres of Merlot with Chambourcin in a cold spot. We also have planted St. Vincent and Aromella.

    Powdery Mildew Risk

    The following link feeds the temperature log into a script that calculates powdery mildew risk index using the Gubler model. The basic idea is that the risk index is used to stretch or shrink spray intervals. If the risk index is 30 or less a spray interval can be stretched to the label maximum. If the index is 40 to 50 a spray interval can be of intermediate length. If the index is 60 to 100 then is high pressure for powdery mildew and spray intervals should be shortened to the label minimum.

    A consecutive 12 hours exposure to UV light plus a leaf temperature of 95 will kill the fungal colonies completely. Because transpiring leaves are usually much cooler than the surrounding air, predicting mildew death based on air temperature measurements may be unreliable. If a mildew colony is not killed by high temperatures, it may still be expanding. The effect of extended high temperatures is not a factor in the Gubler model. The Gubler model raises the risk index even when these high temperatures occur if the 6 hour window of 70-85 has been met.

    Humidity can affect spore germination. Spores can germinate at humidities as low as 20%, but 40% or more results in better germination. Because the humidity within the vineyard and vine canopy is likely to be much higher than the surrounding air, one can assume that germination is successful regardless of the humidity of the surrounding air.