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Cornell University : Cornell Cooperative Extension
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Growing Degree Days |
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Using Growing Degree Days provides a means of relating plant growth to air temperature. In general, the rate of plant growth increases as seasonal temperatures increase. To determine the number of growing degree days, the daily high and low are added together and divided by 2 to determine the mean temperature of the day. One more number is needed to complete the equation. A base figure must be determined according to the crop being grown. Cool season crops will grow when the air temperature is above 40o F, while warm season crops will grow at temperatures above 50o F. In New York, the base selected is usually 50, as the data that has been developed applies mostly to warm season crops. By subtracting the base temperature from the daily mean temperature, the number of growing degree days can be determined. For example, if the high for a day was 80o and the low for the day was 62o, the mean temperature for the day was 71o. Using a base of 50, there were 21 GDD’s accumulated that day. The higher the number of Growing Degree Days, the warmer the day was, allowing the crop to grow faster. The GDD’s can also be tracked through the year, as the accumulation of growing degree days can be used to predict when certain critical points in crop development will occur. They can also be used to predict when insect infestations are likely to occur, as the hatching date of the eggs of many insect species is determined by the Growing Degree Day accumulation. Growing Degree Days can be utilized as an important part of an integrated pest management program in the garden. The base temperature is likely to be different for insects than the one selected to monitor crop development. Cornell
Cooperative Extension Yates Association |
