
How to Manage Pests
DegreeDays: Additional Information
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from Maximum and Minimum Temperatures. Ecology 50(3):514517.
Andrewartha, H. G. and L. C. Birch. 1973. The History of Insect Ecology.
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Allen, J. C. 1976. A Modified Sine Wave Method for Calculating DegreeDays.
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Wilson, L. T. and W. W. Barnett. 1983. DegreeDays: An Aid in Crop and
Pest Management. California Agriculture. 37:47.
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Bentley. 1983. DegreeDays: The Calculation and Use of Heat Units in Pest
Management. University of California Division of Agriculture and Natural
Resources Leaflet 21373.

biofix:
 the date when you begin accumulating degreedays, usually associated with a biological event.

degreeday:
 a unit combining time and temperature, used to measure the development of an organism from one point to another in its life cycle.

double sine:
 one method of simulating a temperature curve for a 24hour period. Two sine curves are fit to the minimum and maximum temperatures for a day and the minimum temperature for the next day. Degreeday calculations are based on the area under the curve and between the threshold(s).

double triangle:
 one method of simulating a temperature curve for a 24hour period. Two triangles are fit to the minimum and maximum temperatures for
a day and the minimum temperature for the next day. Degreeday calculations are based on the area under the curve and between the threshold(s).

horizontal cutoff:
 a modification, in relation to the upper threshold, to the degreeday calculation method. A horizontal cutoff assumes that development
continues at a constant rate at temperatures above the upper threshold.

Huber's:
 a method for calculating degreedays that reduces the total degreeday accumulation if the minimum and maximum temperatures for the day are between the upper and lower thresholds.

intermediate cutoff:
 a modification, in relation to the upper threshold, to the degreeday calculation method. An intermediate cutoff assumes that
development slows as temperatures increase above the upper threshold.

lower threshold:
 the temperature below which development stops.

single sine:
 one method of simulating a temperature curve for a 24hour period. A sine curve is fitted to the minimum and maximum temperatures for
a day, in the assumption that temperatures are symmetrical around the maximum temperature. Degreeday calculations are based on the area under the curve
and between the threshold(s).

single triangle:
 one method of simulating a temperature curve for a 24hour period. One triangle is fitted to the minimum and maximum temperatures for
a day, in the assumption that temperatures are symmetrical around the maximum temperature. Degreeday calculations are based on the area under the curve
and between the thresholds.

threshold:
 (Physiological) the point at which a stimulus is just strong
enough to be perceived or to produce a response.

upper threshold:
 the temperature above which the rate of growth or development begins to decrease or stop as determined by the cutoff method.

vertical cutoff:
 a modification, in relation to the upper threshold, to the degreeday calculation method. A vertical cutoff assumes that development
does not occur at temperatures above the upper threshold.
