Preliminary observation in 1984 indicated that while the cultivar DPL-90 produces a great many abnormal 4-bract squares during early season in Arizona it produces few such squares in Mississippi. Since 4-bract squares are more susceptible to thrips damage and subsequent shedding, the source of the environmental effect on square morphology was sought.

Analysis of weather data from 1984 showed that temperatures in Arizona during the period 20 to 45 days after emergence averaged 82 F while those in Mississippi averaged 79 F. During 1985 temperatures in Mississippi averaged 82 F during the period 15 to 30 days after emergence and many 4-bract squares were observed. These observations suggest that perhaps cotton forms abnormal bracts when temperatures during primordial flower bud formation are in excess of 80 F.