Three "Texas" and six "Delta" cultivars were evaluated at Mississippi State from 1978 through 1982. These five growing seasons varied greatly in accumulated heat units and rainfall. Average yields were higher in the relatively warm, dry seasons of 1978, 1980 and 1981 compared to the relatively cool, wet seasons of 1979 and 1982. The Delta cultivars consistently yielded higher than the Texas cultivars but the cultivar by year interaction was highly significant. This interaction was mainly associated with the relatively high yields of the Texas cultivars in 1979 and 1982.

Lint yields of each cultivar were negatively correlated with heat unit accumulation occurring in May. This correlation was attributed to relatively low yields and high May temperatures in 1982. The yield of CAMD-E, a Texas cultivar, was also negatively associated with high temperatures occurring in June, July, August, and September. In contrast, each of the Delta cultivars had increased yield with high monthly temperatures from June to September. The associations with rainfall were directly opposite, high yields of CAMD-E and the Delta cultivars were associated with high and low rainfall, respectively.

These associations indicate cultivars vary greatly in their response to heat units and rainfall. Precise management practices for growing very early maturing cultivars in Mississippi should be further studied.