I have been receiving a few calls about PGR use on cotton. Factors that must be considered when determining when and how much mepiquat to use include:(1) stage of plant growth, (2) rate of plant growth, (3) pest control and (4) anticipated plantgrowth (irrigation, drought, fertility). Because of the many variables, hard and fast rules regarding the rate and timing of mepiquat are not appropriate. Fields vary in growth. Weather varies by year/location, and thus, recommendations must be flexible.
Data collected each year is used to fit varieties into one of four particular classes of variety responses to PGRs. The first class contained varieties with the most vegetative growth potential, and would require PGR applications in almost all situations. The 2nd class contains varieties with similar vegetative growth potential of the 1st class, yet are more responsive to PGRs or may have earlier maturity. The 3rd class contains varieties in which could require PGR applications, however initiation of PGR applications prior to bloom is not generally necessary and could result in premature cutout, especially in dryland conditions. The 4th class contains varieties which may need no PGR applications or in almost all cases not applied prior to bloom.
This grouping of varieties into classes was developed to simplify PGR decisions based on variety and help growers make more education decisions when planting varieties for the first time. When a new variety is planted, PGR decisions could be based on its PGR classification due to being in the same class as a more familiar variety or because it is in a different class than a familiar variety. This system was also developed so that future investigations of PGR needs of new varieties can be more easily evaluated and quickly determined. Below are suggestions on PRG Requirements on cotton varieties from Dr. Jared Whitaker, UGA Cotton Agronomist.