Critical Temperatures For Concord Grapes

			EB1615


More wind machines and sprinklers in vineyards mean increased interest in critical temperatures for frost protection. The National Weather Service publication "Frost and the Prevention of Frost Damage" gives 30° for closed buds that show color. That is not enough information. Preliminary research has given some rough estimates of what temperatures would be expected to kill primary buds. As the buds become active, swell, open and begin growth, they become more susceptible to frost injury. Also, in any vineyard some buds are more susceptible or resistant than others to low temperatures. These are expressed as T₁₀, temperatures likely to kill 10% of the primary buds, and T₉₀, temperatures which are estimated to kill 90% of the primaries. The values shown in the table below were determined in the laboratory and have not been checked extensively against field injury. Further, the test procedures were modified in 1977. Therefore, the data represent only one season's experience. In spite of these limitations, these values are distributed as a guide to what might be expected on cold nights. These estimates also provide a basis to which growers can relate their experiences of field injury.

Stage of Development	Definition	Critical Temperatures*
		T₁₀	T₉₀
Dormant	Closed bud, inactive	variable	subzero
First swell	Buds increase in size, scales separate to show brown, fuzzy, young leaf tissue	13	-3
Full swell	Buds swell further, young leaves become pink. Still closed around growing point	21	10
Bud burst	Young leaves separate at tip to show the growing point	25	16
1st leaf	First leaf is out of the bud, makes right angle with stem	27	21
2nd leaf	2nd leaf makes right angle with stem	28	22
3rd leaf		28	26
4th leaf		28	27
5th leaf		28	27

*Critical temperatures for 10% (T₁₀) and 90% (T₉₀) kill of primary buds.

E.L. Proebsting, former Washington State University horticulturist, V.P. Brummund, former WSU research aide, and W.J. Clore, former WSU research horticulturist, WSU Prosser.

College of Agriculture and Home Economics

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