Agricultural management decisions are often timed on the basis of accumulated air temperature heat units (AT-heat unit) to coincide with crop growth and development. The relationship between AT-heat unit accumulation and crop development is affected by water deficits that alter the relationship between air and plant canopy temperature. Improved technology for monitoring canopy temperatures makes it possible to continuously monitor canopy temperature in production settings. The utility of cotton canopy temperature heat units (CT-heat unit) was assessed by comparing decadal (2000-2009) AT-heat unit variation with variation in CT-heat unit accumulation due to variable irrigation in 2009. Irrigation-induced variation in CT-heat units (1198-1416) was similar to the decadal variation in AT-heat units (1270-1508). Two heat unit-based management tools: 1) the assignment of irrigation crop coefficients and 2) the identification of a fiber thickening period were both found to be sensitive to irrigation-induced changes in CT-heat unit accumulation. The inclusion of CT-heat units resulted in variability in both indicators that reflected effects of irrigation and climate on plant performance. Inclusion of canopy temperature measurements in heat unit accumulation might improve the utility of heat units.