MONDAY, APRIL 18, 2022. BY STEPHANIE BOLTON, STAN GRANT, and MATT WANINK.
Featured image showing frost damage on young shoots in the Lodi AVA (Peltier Rd & Davis Rd), courtesy of Lodi Winegrape Commission Board Member Bruce Fry of Mohr-Fry Ranches.
Since March 1, the Lodi Winegrape Commission and Western Weather have provided an afternoon Frost Forecast to growers based upon data from 37 weather stations. This forecast is in addition to the Daily Weather Forecast issued around 6:30am. Growers may access these forecasts on the custom Lodi Weather website or they can sign up to receive forecasts by email.
With temperatures reaching record highs of over 90 degrees F in early April, it seemed a bit ridiculous to have the extra Frost Forecast – until a frost event on the morning of April 12, 2022, reminded everyone why these forecasts are so important.
The table below (which you can click on to enlarge as a PDF) shows the temperature reading on the hour for 39 weather stations from April 11-12, which cover not only the seven Lodi sub-AVAs but also areas to the west and south of the Lodi AVA. Temperatures at or below freezing (32 degrees F) are shown in the white cells and the minimum daily temperature is shown for each station on the bottom row.
Note that 16 of the 39 weather stations recorded a daily minimum temperature of at or below freezing on April 12. The lowest recorded temperature in the Lodi AVA, experienced in Sloughhouse, was 27.9 degrees F.
Western Weather’s Matt Wanink summarizes the frost event below:
“An unseasonably cold upper-level trough of low pressure, that originated in the Gulf of Alaska, plunged SE’ward over Northern California last Monday, April 11. A cold front associated with the trough brought scattered showers (averaging 0.10″ – 0.20” of rain) to the Lodi area with its passage through the morning hours. The cold front also dropped over a foot of snow in the higher elevations of the Sierra Nevada during the afternoon; the snow level dropped down to 4000ft by the end of the day. Breezy NW winds in the wake of the front Monday afternoon in the valley caused dew point temperatures across the Lodi area to drop into the middle to upper 20s by sunset. Clearing skies and easing winds overnight set the stage for freezing temperatures by dawn Tuesday with the coldest wind-sheltered locations seeing lows in the upper 20s.”
Stan Grant tells us in a past lodigrowers.com blog post, “Frost Management Strategies for Vineyards,” that grapevines are most susceptible to frost damage when they are located at high elevations, in low-lying areas where cold air settles, and next to obstacles to air movement, such as orchards, tall riparian vegetation, levees, and buildings. Even within vineyards that appear open and flat, there may be some sections that repeatedly sustain frost damage due to reoccurring settling of cold air. Be sure to read Stan’s article for frost-related advice – including what to do after a spring frost.
Photos of the April 12 frost event’s damage in a Thornton vineyard, courtesy of Bruce Fry:
Lodi Winegrape Commission Executive Director Stuart Spencer found more great frost damage resources by using the search tool on our website. Notably, a “Spring Frost Damage” article by former Lodi Viticulture Farm Advisor Jim Kissler offers the following answers to typical post-frost questions:
- Why are the shoots at the top of my vines green and the lower ones burned? The area of lowest temperatures during a frost occurs at the surface of the soil, OR if there is a cover crop, it occurs at the top of this vegetation. Obviously it is desirable to lower this zone of cold air as much as possible. A cover crop mowed short results in less frost hazard than a cover crop 1 to 3 feet high. Bare soil receives heat that is stored during the sunlight hours and released at night. Therefore, a firm, bare soil can raise the air temperature around the vines as much as 2 to 3 degrees. Vines trained on a high trellis may escape a frost.
- Should I fertilize my frosted vineyards now? NO! Fertilizers applied late in the spring could cause late vegetative growth which won’t harden off in the fall; thus, winter damage may occur to the new wood (especially on some varieties). (This advice is referring to extra fertilization to try and encourage better yields – Viticulturist Stan Grant reminds us not to cut corners on bloom nutrition to ensure as many remaining flowers as possible set fruit).
- Should I break out the frosted shoots? NO. Research work done by A.N. Kasimatis and J.J. Kissler in San Joaquin County in 1972 showed that breaking out the frosted shoots reduced the yields; so leave them alone!! (Research results reported in the American Journal of Enology & Viticulture, Vol. 25, No. 1, pp. 17-20).
- Should I continue to sulfur my damaged vines? Yes. If you have green growth with new growth pushing, follow a regular dusting program. Powdery mildew, once established, is difficult to eradicate.
- Would an irrigation help my frosted vines? Irrigation should be determined according to the available moisture in the soil. If an irrigation is needed, then irrigate. I think it is important to apply the first irrigation before the soil becomes too dry – you’ll get better penetration.
A 2008 “Frost Information Guide” presentation (which we think was by former Lodi Viticulture Farm Advisor Paul Verdegaal) also found in Stuart’s lodigrowers.com search reminded us of former spring frost dates in Lodi. The summary slide offers further tips for growers experiencing spring frost damage.
Stan Grant adds that with fewer berries per vine, growers may be able to decrease irrigation and K for the growing season and save a bit of money there.
Spring frost damage is one of those “wait and see” scenarios, where you hope for the best and where it is important to communicate with your winegrape buyers. For Lodi growers, PCAs, and viticulturists experiencing the April 12 frost who want to get together to discuss it in an affected field, the Commission is planning a small gathering this Friday, April 22, 2022 at 11am in a Thornton vineyard. Email firstname.lastname@example.org to sign up and get more details.
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