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Bud break and risk of frost / freeze damage

I am hearing reports of 10-15% bud break in early-breaking cultivars such as Chardonnay and Merlot planted across Cleveland and Dahlonega.  Perhaps this is also occurring in Blanc du Bois is west Georgia, and in Chardonel at lower elevations. Buds may still be either at the dormant bud or bud swell stage at higher elevations in Ellijay, Young Harris/Blairsville, and Tiger.

Please check your local weather forecast tonight and tomorrow night to see if you are at risk of experiencing the predicted advective freeze event at your site. The coldest temperatures are predicted to occur on early Thursday morning, when the wind speeds start to settle down.

There are several frost protection methods, and a forthcoming extension publication that explains many of these can be found below in the “Further Reading” section.  Many here in Georgia practice delayed pruning to delay bud break in the basal buds that will be retained when final spur pruning.  Hopefully basal buds are less advanced than apical buds in delay-pruned vineyards, as tissue sensitivity to cold increases as growth stage advances (Sugar et al. 2003).  Air mixing via wind machine use is the most common form of vineyard frost protection used here in Georgia and other eastern US regions.  While air mixing with a wind machine can raise the temperature roughly 1-3 degrees F over 10-12 vineyard acres, it is primarily effective when used during radiation frost events – when an inversion occurs due to cold air settling below warm air.  It is documented that a wind machine (and other active frost protection methods) is a less effective frost avoidance tactic in advective freeze conditions, such as those forecasted between late tonight and early Thursday morning. Vineyard heaters and sprinkler irrigation are other frost protection methods.  However, those are less popular methods than wind machines, perhaps because of the associated labor (heaters) and/or the need to be extremely cautious about wind speeds, dew points, and flow volumes for effective implementation (irrigation).

My advice: know the forecast at your specific location, know the stage of your buds in your susceptible cultivars (mentioned at the top of this post), and know the relative efficacy of your frost protection options during the forecasted frost / freeze events.  For those that do not have active frost protection options – try to get a good night’s rest, there’s not much you can do.  For those that are still dormant or barely swollen – it may not get cold enough over the next two days to cause injury and thus may not warrant the implementation frost protection measures.  For those that are seeing bud break in early cultivars (i.e. Chardonnay and Merlot) – stay in tune with your local weather and make judicious decisions based on the relative efficacy of your frost protection method during the predicted advective freeze conditions.  However, be alert and prepared for the predicted coldest temperatures and settling wind speeds on Thursday morning.

A sincere BEST OF LUCK to all.

Cain

 

Further reading:

Hellman, E. 2015. Frost injury, frost avoidance, and frost protection in the vineyard. eXtension online article, Sep. 6, 2015. http://articles.extension.org/pages/31768/frost-injury-frost-avoidance-and-frost-protection-in-the-vineyard

Poling, E.B. 2007. Overview of Active Frost, Frost/Freeze and Freeze Protection Methods. In Proceedings from Understanding and Preventing Freeze Damage in Vineyards. R.K. Striegler et al. (organizing committee) pp. 47-64. University of Missouri, Columbia, MO.

Striegler, R.K. 2007. Passive Freeze Prevention Methods. In Proceedings from Understanding and Preventing Freeze Damage in Vineyards. R.K. Striegler et al. (organizing committee) pp. 39-46. University of Missouri, Columbia, MO.

Sugar, D., R. Gold, P. Lombard, and A. Gardea. 2003. Strategies for frost protection. In Oregon Viticulture. E.W. Hellman (Ed.) Oregon State University Press. Corvallis, Oregon.

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Missouri Freeze Conference Proceedings