Boll weevil eradication in parts of the southeast USA may have resulted in a wider planting date window in which economic cotton yields can be achieved. This research was conducted to determine the influence of planting date on cotton yield, fiber quality, and yarn strength. Advanced Pee Dee germplasm lines and 'PD-3' were planted approximately May 1 and June 1 in 1987, 1988, and 1989. Experimental design was randomized complete block in split-plot arrangement with four replicates. Main plots were planting dates. Standard recommended cotton production practices were used and the soil type was Norfolk sandy loam.

Significant year X planting date interaction occurred for lint yield, micronaire, 50% and 2.5% span length, elongation, fiber strength, and yarn strength. An extended dry period during July of 1987 caused square and boll shed in the early planting, but not the late planting, but not the late planting. There was greater yield with late planting that year. In 1988, cool May temperatures together with a dry period in August resulted in similar yields between the planting dates. In 1989, Hurricane Hugo caused extensive damage to the immature late-planted cotton, and caused yields from that planting date to be reduced.

The year to year variability in the timing of these weather conditions had more impact on the yield response to planting date than on fiber and yarn properties. In 1987, there was no difference between planting dates for length or fiber strength. Late planted cotton had slightly lower micronaire and higher elongation and yarn strength than early planted in 1987. In 1988, early planted cotton had higher fiber strength and micronaire than late early planted. In that year, values for elongation and yarn strength did not differ between the planting dates, and late planted had longer fibers. In 1989, plant damage from Hurricane Hugo caused immature boll opening which resulted in reduced micronaire for the late planting date, but length, elongation, and fiber and yarn strength were all greater with late planting that year.

Significant higher order interactions with genotypes, years, and/or planting dates occurred for all variables. These interactions, however, generally had small mean squares (compared to year, planting date, and year X planting date mean squares) and their nature was mainly of magnitude, not rank.

The results of this study suggest that, in comparing early may to late May planting, the year to year variability in the occurrence of prolonged dry periods and other weather conditions determine the yield of cotton to a greater extent than does planting date by itself. Also, within year weather differences affected lint yield more than yarn strength or the fiber properties measured.