RT Journal Article
SR Electronic
T1 Some Limitations of the Degree Day System as Used in Viticulture in California
JF American Journal of Enology and Viticulture
JO Am J Enol Vitic.
FD American Society for Enology and Viticulture
SP 128
OP 132
DO 10.5344/ajev.1987.38.2.128
VO 38
IS 2
A1 G. N. Mc Intyre
A1 W. M. Kliewer
A1 L. A. Lider
YR 1987
UL http://www.ajevonline.org/content/38/2/128.abstract
AB The average and range in dates of budbreak, bloom, and fruit maturity of five grape cultivars grown in five different climatic regions of California were determined over a period of two to six years. For each cultivar and climatic region, a comparison of the variation in the average number of degree days and duration (in days) for three developmental periods (budbreak to bloom, bloom to fruit maturity (20°Brix), and budbreak to fruit maturity) was made. No statistically significant difference was observed between the two procedures. Determining the number of degree days by digitizing the area under the thermograph curves for five different locations gave degree day values for the period 1 April to 31 October that ranged 6% to 22% lower than the traditional method of mathematically averaging the maximum and minimum temperature per day. For a given cultivar, there were wide differences in the number of degree days required for the developmental periods between the five locations. Possible reasons for these differences are discussed.