Learning about frost avoidance to get grapevines through that dangerous period of temperature fluctuation in the spring has been up and down over the past three years. It's one thing to get the vines through a cold winter in fine shape but quite another to see healthy primary buds with inflorescence primordia die overnight because of a sudden drop into the freezing temperatures and thus a loss of the crop for the season.
2004 has been a test year for frost research. March was one of the warmest on record. Alginate treatment was applied on 19 March after a week of 70F temperatures made me scared that budding would occur soon. 19F on April 11 killed the primary buds of early varieties like Foch and Millot that were not treated and had started to swell. Temperatures below freezing also occurred on April 24 and 29. Each cold morning brought damage to untreated buds on the earlier budding varieties. Between these cold nights most days had temperatures between 60F and 80F. By the first of May, the temperatures were consistently in the 80's and some of the treated vines (at the 90% dilution) were swelling. I was pleased to see that they were starting bud swell along with the untreated, latest budding varieties, such as Melody. Coinciding with our avg. last frost date, temperatures dipped to 28F on the 13th of May accompanied by a heavy, wet snow.
I've struggled to find the means of either avoiding the frost by keeping the buds dormant longer or to impart a greater frost tolerance to the shoots and leaves once they have emerged. There are many chemicals on the market that promise to protect the shoots and leaves to 25F. I've tried them all and none have worked.
I settled upon the frost avoidance scheme of delaying bud burst. I had two lines that I originally pursuited: soybean oil and sodium alginate. Soybean oil proved to be a disaster from the beginning. Developed by a midwestern university, this would have been ideal. It can be sprayed on conveniently and efficiently, thus useful for commercial vineyards. Unfortunately, I found that there was a 40-60% bud mortality (depending upon the variety) with the use of soybean oil. Nothing like killing the buds you are trying to save.
Sodium Alginate was developed at Colorado State University by Dr. Cecil Stushnof and Imid Dami. This chemical formulation keeps the buds in dormancy by osmotic potential and somewhat with physical pressure on the bud. When I first began using the alginate, it had one big drawback in that it washed off the buds in heavy rain and over time when small, light rains or wet snows occured. This meant having to re-apply it regularly for it to remain effective. This year I added 10% latex paint to the mixture to improve its "staying power".
The alginate was applied at two rates: full strength and at 90% (diluted with 10% water so that it could be applied efficiently with an airless sprayer as might be done commercially). Unlike previous years where multiple applications were needed for protection, I made one application to evaluate the latex addition to the mixture. The intent was to see if the latex addition would suffice in allowing maximum protection throughout the spring frost threat and, with the diluted mixture, to see if a slight thinning to allow for spray application would affect the overall efficiency of the treatment.
A brief overview of the early budding variety, Foch, should be sufficient to summarize the results of the experiment:
| date | bud stage (control) | % Primary bud kill (control) | bud stage (alginate) | % Primary bud kill (alginate) | Bud stage (90% dilute alg) | % Bud kill (90% dilute alg) |
| 12 Apr | bud swell to woolly | 30% | dormant | 0% | dormant | 0% |
| 26 Apr | woolly | 40% | dormant | 0% | dormant | 0% |
| 1 May | woolly to 1st leaf | 60% | dormant | 0% | bud swell to woolly | 0% |
| 14 May | 1st leaf to 1 inch shoot | toast (dead) | dormant to woolly | 0% to 20% | woolly to 1st leaf | some freezing injury* to toast (dead)** |
As can be seen from the above simple table, the full strength alginate treatment prevented bud burst and frost injury. (But not what I would have liked by treating more than once.) The diluted alginate also allowed for protection but the canes treated began swell and burst earlier than the full strength treatment. Unfortunately, those buds that had pushed beyond the first leaf stage completely died after the freeze on the 13th of May. Untreated vines displayed increasing injury with each successive frost episode. It should be noted that secondary buds pushing from damaged buds were later killed in most instances.
A greater protection would have been possible with the application of the treatment twice during the frost season This would be highly desirable in areas where heavy rains would affect the outcome. And, this is especially recommended if diluting the alginate treatment for spray application.
I'm continually trying to improve this product and its efficiency. With this year's research, I now realize that a minimum application of two treatments are needed to maintain dormancy through the frost threat period. New additions are already being considered and will be experimented with next year. The alginate treatment may be purchased at: Rist Canyon Vineyards.With the last frost episode and the predictions of 70F weather for the next week, I hope this year's frost danger is now a thing of the past. I guess much of this season's research will be devoted to studying the yields of secondary buds after a late frost event. Onward into the growing season!!
Ft. Collins Temp
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Neron (a Kuhlmann hybrid) at harvest time in early September, 2003. Hardy, vigorous, productive.