Hormesis Effect of Dichlorophenoxy Acetic Acid Sub-Doses and Mepiquat Chloride on Cotton Plant

<div><p>ABSTRACT: The aim of this study was to evaluate the hormesis effect of sub-doses of dichlorophenoxy acetic acid herbicide and the plant growth regulator mepiquat chloride on the vegetative and productive characteristics of two cotton cultivars (FMT 701 and Fibermax 966). The experiment was conducted from November 2013 to May 2014. The experimental design was a randomized block in a factorial scheme 6 x 2 x 2, with four replications, totaling 96 installments with 24 treatments: the witness and five sub-doses of the herbicide 2,4-D: 0.68, 1.36, 2.04, 2.72 and 3.40 g equivalent acid (e.a) per ha, with and without application of mepiquat chloride at a dose of 200 mL ha-1 in the cotton cultivars FMT 701 and Fibermax 966. The sub-doses applied were 2,4-D at 45 days after the emergence of the plant (DAE), and the growth regulator was applied at 70 DAE. It was found that the use of the growth regulator (mepiquat chloride) at a dose of 200 mL ha-1 was effective in controlling plant development relative to its variable height. The application of sub-doses of 2,4-D up to 1.75 g e.a ha-1 provides increased seed cotton productivity FMT 701 and Fibermax 966). The cultivar FMT 701 got greater plant height, stem diameter, number of reproductive branches, bolls per plant and seed cotton productivity compared to the cultivar Fibermax 966.</p></div>