Six field experiments were carr ied out in 1977/78 at several regions of São Paulo State: Jardinópolis, Leme, Salles Oliveira, Santa Bárbara D'Oeste and São João da Boa Vista, to know the mepiquat chloride action as a phytoregulator on cotton plants. A design of randomized blocks, with four replications was used for the experiments. The treatments were four increasing doses of mepi16 quat chloride: 25, 50, 75 and 150 g/ha compared with an untreated check. Results were evaluated by cotton he ight, lateral branches growth, fall of leaves, ball number in each plant, damaged balls/undama - ged balls, agronomic characteristics as yield, fiber rate, seed germination and 100 seeds' weig ht, technological characteristics of fiber, as span lenght, uniformit y ratio, micronaire, strength and maturity. Statistical analysis of data showed that the mepiquat chloride caused a decrease in plant height, number of rotten apples, fiber rate, but it didn't cause damage to cotton yield, fiber quality or seed germination.
mepiquat chloride; cotton; fiber yield; fiber quality