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Cotton Boll Period Response to Water Stress and Pink Bollworm¹

Rapid cotton (Gossypium hirsutum L.) boll development and opening can be beneficial in late season. It can result in increased lint yield, earlier harvest, higher grade, less insecticide use, and reduced storm damage. Research was conducted in the field on a fine loamy, mixed (calcareous), hyperthermic, Anthropic Torrifluvent soil. This study evaluates the effects of water stress in late season (early irrigation termination) and pink bollworm [Pectinophora gossypiella (Saunders)] infestation on time required for cotton bolls to develop from flower to open boll in the field. Water stress speeded boll opening. Bolls from stressed cotton were obtained from field tests with five dates of final irrigation. They opened an average of 17 days earlier than bolls of unstressed cotton in late season. Boll period averages ranged from 41 to 76 days depending upon the degree of water stress and time of year. On droughty (shallow) soil [fine loamy, mixed (calcareous) hyperthermic Anthropic Torrifluvent], water stress effects were significant, but smaller. Delayed boll opening may explain reduced lint yield which at times is associated with late final irrigation. Pink bollworm infested bolls opened about 3 days earlier than non-infested bolls in two tests with deep soil, but only 0.5 days earlier in a test on droughty soil. Boll period population resembled a normal distribution around the mean until 93% of the bolls were open. For a given day of flowering, 80 % of the bolls (from 10 to 90 % ) opened within a 8- to 11-day period.

Key Words: Gossypium hirsutum L. • Gossypium barbadense L. • Pectinophora gossypiella (Saunders) • Boll maturation

² Agronomist, entomologist, entomologist, agronomist, and plant physiologist, respectively. Agronomists and plant physiologist at Plant Sciences Dep., Univ. of Arizona., Tucson, AZ 85721 and entomologists at Western Cotton Res. Lab., USDA, ARS, 4135 East Broadway, Phoenix, AZ 85040.

Received for publication December 11, 1981.