Cotton is a perennial plant with an indeterminate growth habit. However, cotton varieties have varying levels of indeterminacy. Indeterminacy can also be viewed as “strength of terminal growth” during the fruiting window (prior to cutout). Vegetative growth and fruiting occur concurrently in indeterminate varieties. Within each maturity grouping, some varieties exhibit more indeterminate growth and fruiting. Varieties with greater levels of indeterminacy may require more time and a greater level of a plant growth regulator (PGR) to control vegetative growth and maturity. Varieties with a less indeterminate nature are more responsive to PGR applications and may require less growth management.
Cotton farmers may select varieties based primarily on yield potential rather than degree of indeterminacy. However, understanding the degree of indeterminacy of a variety can offer some benefits when placing and managing.
More indeterminate varieties will generally withstand stress better than less indeterminate varieties and can be placed in more stressful, tougher soils and growing conditions. More indeterminate varieties can sustain terminal growth and fill the canopy better than earlier maturing varieties. These varieties will continue to make nodes and produce fruit even during periods of stress. Less indeterminate varieties fruit faster and are typically best suited to more productive soils and more intensive management (irrigation, PGRs, fertility). While node counts may be similar prior to bloom, more indeterminate varieties sustain the rate of node development after bloom, while the less indeterminate type begins to slow terminal node development much quicker, moving more quickly to cutout (Figure 1).
Because more indeterminate varieties continue adding nodes after fruiting starts, maturity can be delayed. A heavy boll load will cause the plant to put more energy into developing bolls, slow vegetative growth, reduce nodes above white flower (NAWF), and move the plant toward cutout. Stress, such as drought, can reduce leaf area and internode length, slowing the development of nodes. Farmers can apply PGRs to reduce vegetative growth and slow terminal growth (Figure 2).
Cotton specialists encourage growers to monitor cotton plant growth during the season and to apply PGRs to control excessive vegetative growth, particularly in more indeterminate cotton varieties. Examples of cotton variety growth characteristics and their relative degree of indeterminacy are in Table 1.