Fruiting of Upland and Pima Cotton with Different Planting Dates1

Abstract Interest in short‐season cotton production is increasing because of late‐season insect problems and, in the West, because of the expense of irrigation. Diverse cultivars of Upland cotton ( Gossypium hirsutum L.) and American Pima cotton ( G. barbadense L.) were compared at Phoenix, Arizona to evaluate short‐season production using several planting dates in 3 years and three dates of final irrigation in one of the years. The soil was a fine‐loamy, mixed (calcareous), hyperthermic, Anthropic Torrifluvents. Lint yield of Upland cotton was not reduced when planted as late as 7 May, except when irrigation was terminated in mid‐August. In contrast, lint yields of Pima cottons were reduced with each later planting date, except for the earliest planting and latest irrigation and harvest. Plant populations in 2 years had no interaction with planting dates for lint yield. The dates of seedling emergence and dates of early flowering occurred about the same time for Upland and Pima cotton in most plantings and therefore could not account for the differences between species in yield response to dates of planting and final irrigation. The rate of flowering, once started, was much slower for Pima cotton than Upland cotton. ‘Pima S‐5’ reached peak flowering an average of 18 days later than ‘Deltapine 61’ (DPL 61). Weekly lint production far DPL 61 was 4.5 times that for Pima S‐5 in August, twice that of Pima S‐5 in September, but only three‐fifths that of Pima S‐5 in October. Pima strain ‘79–106’ was intermediate between DPL 61 and Pima S‐5 in earliness of lint production. We conclude that Pima cotton requires early planting and nearly full‐season production for highest yield. Early planting is not as critical for Upland cotton, unless early crop termination is planned.