Recent rains and warmer temperatures should result in very rapid plant growth over the coming weeks. For those who have not applied an early shot of a plant growth regulator (PGR), you should consider doing so very soon. Remember, PGRs do not shrink the plant; instead, they ultimately reduce internode elongation (among other things). Although yield increases due to PGR applications are not consistent, PGRs consistently increase the penetration of insecticides into the canopy and increase harvest efficiency. Therefore, it is very important under conditions like these to expand calendar or growth-stage based PGR application programs to consider some in-field measurement of plant growth and adjust rates and/or application timings accordingly.
Ideally, height-to-node ratios during the period between large square to first flower should fall between 1.2 – 1.7 inches/node. A more rapid measurement focused only on present plant growth considers the internode length between the fourth and fifth nodes. If this internode is between 2 to 3 inches, growth is considered to be adequate. If this internode exceeds 3 inches, however, the potential for rank growth is high. The main goal here is to use PGRs to govern vegetative growth until the reproductive sinks begin to naturally govern vegetative growth. Given fruit retention is adequate, the transition to reproductively governed vegetative growth should occur during the effective flowering period.
Several PGRs are currently available, but results of a regional Beltwide study noted no significant differences in effectiveness of formulations of mepiquat chloride, mepiquat chloride + kinetin, mepiquat chloride + cyclanilide, and mepiquat pentaborate when used at equivalent rates (Dodds et al., 2010). Other factors which should be considered when selecting rates and timing(s), including variety sensitivities, can be found in Dr. Chris Main’s June 22, 2012 post and the UT Cotton Production Manual.
Dodds, D.M., J.C. Banks, T. Barber, R. K. Boman, S.M. Brown, K.L. Edmisten, J.C. Faircloth, M.A. Jones, R.G. Lemon, C.L. Main, C.D. Monks, E.R. Norton, A.M. Stewart, and R.L. Nichols. 2010. Beltwide evaluation of commercially available plant growth regulators. J. Cotton Sci. 14:119-130.
