Cotton responses to mepiquat chloride and PGR-IV treatments

Abstract

Plant growth regulators (PGRS) are applied to cotton (Gossypium hirsutum L.) to control vegetative growth, increase yields and hasten maturity. Two of these PGRS, mepiquat chloride (MC) and PGR-IV, affect plant growth in different ways. MC inhibits the formation of the naturally occurring plant hormone gibberellic acid (GA), whereas PGR-IV adds GA to the plant. The effects of MC and PGR-IV on yield have been erratic. Several plant characteristics, including height, are altered by these compounds. The application of MC causes plants to be shorter while PGR-IV treatment often results in taller plants. The use of sequential applications of these PGRs to obtain increased yields and height control has been questioned. The objective of this study was to determine if the combined use of MC and PGR-IV exceeded the effectiveness of either of these PGRs used alone. Field experiments containing an untreated control, a MC treatment, a PGR-IV treatment, and a treatment of both MC and PGR-IV applied sequentially were conducted in 1996 and 1997 at the Texas A&M University Agricultural Experiment Station near College Station. Plant heights of cotton treated with PGR-IV+MC were similar to or less than untreated cotton, and, in 1997, the total number of nodes on plants treated with PGR-IV+MC was less (17.6) than that on plants treated with PGR-IV (1 8.4) at mid-bloom. Total flower production of the PGR-IV+MC treatment was intermediate to the MC and PGR-IV treatments. No differences in lint yield were found between PGR treatments for the hand-harvest or the machine-harvest. In the individual boll harvest, lint yields were 1036, 1226, 1158, and 1214 kg ha-' for the untreated control, and the MC, PGR-IV and MC+PGR-IV treatments, respectively. No differences in crop earliness were obtained. In this study, the use of sequential applications of PGR-[V and MC in a program to increase yields and promote early maturity in cotton production did not perform better than either PGR used alone.