Rainfall intensity and Mepiquat Chloride persistence in cotton

Abstract

In some regions where cotton is grown in Brazil rainfall amounts to about 2,000 mm per year, which imposes a great risk for Mepiquat Chloride (MP) to be washed from cotton leaves before being absorbed. The objective of this research was to evaluate the MC persistence when applied on cotton plants submitted to different rain intensities after spraying. The treatments were three MC rates: 0, 15.0 and 30.0 g a.i. ha -1 and four simulated rainfalls, applied 90 minutes after MC spraying: 5, 10, 20 and 40 mm, plus a treatment without rain. Cotton plants of the cv. Delta Opal were grown in 12 L pots filled with an Haplortox. The experimental design was consisted of complete randomized blocks, in a factorial scheme, with four replicates. The evaluated parameters were: plant height, number of reproductive branches, dry matter weight, reproductive structures, retention and leaf area. The higher the rainfall the lower the effectiveness of the plant growth regulator in controlling plant height. A simulated rainfall as low as 5 mm occurring 90 minutes after MC application was enough to wash some of the plant growth regulator from cotton leaves.

Growth regulator losses from cotton plants due to rainfall

“…However, no differences were observed when the results obtained for plants treated with PGR were compared with the control. Similar finding was reported by Souza and Rosolem (2007) when they applied mepiquat chloride and simulated rainfall after 90 min and the number of cotton reproductive structures was not affected. Effects of these growth regulators on fruit retention have been inconsistent.…”

“…Thus, smaller plant height and dry matter production were observed even without the complete absorption of the growth regulators. Similar results were found by Souza and Rosolem (2007), but Mateus et al (2004) observed a compensatory gain due to leaf thickening and an increased leaf area, despite the reduced height after the application of mepiquat chloride, which did not affect cotton plant dry matter. Total growth of cotton plants measured between the application of the regulators and plot disassembly was larger when mepiquat chloride was applied (Table 4).…”

“…Differences were only observed for the interactions among treatments. The effect on the number of reproductive branches may vary according to growth regulator rate (Lamas, 2000), time and amount of simulated rainfall (Mateus et al, 2004;Souza and Rosolem, 2007). The number of nodes in the main stem is important for cotton yield for fruiting branches are formed from these structures (Mauney, 1986).…”

“…The effects of mepiquat chloride and other bioregulators on cotton plants depend on several factors such aslike temperature and rainfall (Athayde and Lamas, 1999). Mateus et al (2004) and Souza and Rosolem (2007) found that the simulation of rainfall right after mepiquat chloride application increases its losses; rainfall and growth regulator dose also influence product washing.…”

“…Mateus et al (2004) worked with mepiquat chloride on cotton and observed that a 10 mm rainfall is enough for PGR washing. For the same PGR, Souza and Rosolem (2007) found that a 5 mm rainfall decreases its effects, regardless of the dose. Therefore, it is interesting to determine the need and rate of PGR to be reapplied and it is important to know whether PGR losses and reapplication would be different for distinct products.…”