Acceleration of Boll Dehiscence with Desiccant Chemicals

Maturity of cotton (Gossypium hirsutum L.) plants is sometimes delayed and some top bolls may not have opened by the first hard freeze in the fall. The result is often a significant economic loss to the grower. The objectives of this research were to investigate the drying pattern in cotton bolls during the final stage of development and to evaluate the effects of desiccant-type harvest aid chemicals in altering the boll drying process and dehiscence rate. One greenhouse study was conducted to measure moisture loss from the bur and seed cotton fractions of treated and untreated bolls during the fiial stage of maturity. Two field studies were conducted to determine the effects of desiccant chemicals on yield components, fiber properties, and dehiscence rate of bolls that developed late in the growing season. The greenhouse plants were sprayed with 187 liters/ha of a 1.5% aqueous solution of arsenic acid and those in the field were sprayed with either sodium chlorate, paraquat, or arsenic acid at 6.72, 0.14, and 5.39 kg/ha, respectively. Drying of untreated greenhouse-grown cotton bolls prior to dehiscence occurred primarily in the interior or seed cotton fraction of the boll. Moisture content of the bur remained at near 80% until just before dehiscence, whereas that of the seed cotton fraction declined at a near linear rate from 78% in 38-day-old bolls to 53% in 50-day-old bolls. Moisture loss from both fractions was accelerated by treatment of the bolls with arsenic acid, but the loss was more pronounced in the bur than in the seed cotton fraction. Boll dehiscence on field-grown plants in 1975 and 1976 was influenced by the environment. The dehiscence rate during both years, however, was accelerated in plots treated with either arsenic acid or paraquat. A trend toward increased dehiscence occurred also in the sodium chlorate plots, but the differences were significant during 1975 only. Dehiscence in the arsenic acid plots was greater than in any of the other plots during both years. None of the chemicals had any adverse effects on any yield component or fiber property. This research indicates that desiccant-type harvest aid chemicals can be used to increase the percentage of bolls harvested from a late developer crop without loss of fiber and seed quality.