Plant Growth Regulator Management in Cotton Cultivars

The major area of cotton production in Brazil is within the Brazilian Savannah and the excessive amount of rain on the first months of the crop alternated with sunny, warm days may result in plant rank growth. Cultivar and weather variability make PGR management more complex. The purpose of this work was to evaluate yield and fiber quality of cotton cultivars under a new method of PGR recommendation as compared with a traditional management that has been employed. Treatments resulted from a combination of eight cotton cultivars (FMT 709, FM 993, IMA 1318, IMACD 8276, IMACD 6001, IMACD 6035, IMA 3869 and FM 966) and two PGR managements. PGR management consisted in a procedure commonly used by growers and the use of a table of recommendation, ant it took into account cotton daily growth rates and degree-day accumulation. Cultivars had different requirements for PGR rates, with a lower rate on early cycle cultivar compared with mid and full cycle cultivars, when PGR application was based on table of recommendation. Boll weight increased by 10% (cultivars FM966, IMACD6001 and IMACD8276); remained unaffected (FM993, IMACD6035, IMACD3869 and IMA1318) or decreased by 14% (FMT709) when plants were treated with PGR based on table of recommendation. PGR management did not affect cotton lint yield. Micronaire increased on cultivars FM966, IMA1318 and IMACD8276 when PGR was applied based on the table of recommendation, while fiber length did not. This new method can help cotton producers to define the right PGR rate in a specific growing situation, i.e., cultivar specificity and environment condition, avoiding the lack or excess of PGR rates.