Abstract
The objective of this study was to evaluate the effect of rainfall on the effectiveness of herbicides applied post-emergence on plants of Senna obtusifolia. The experiment was carried out under green-house conditions and the experimental design was completely randomized design with four replications, with treatments in a 7x8 factorial arrangement (seven herbicides treatments and eight rain intervals). The herbicides used were five formulations of glyphosate (Roundup Original, Roundup WG, Roundup Transorb, Roundup Transorb R and Roundup Ultra) applied at a rate of to 1,080 g a.e. ha-1, glufosinate-ammonium (Finale) at 400 g a.i. ha-1 and 2,4-D (DMA 806) at 1,000 g a.e. ha-1. The rain simulation occurred at intervals of 15; 30; 60; 120; 240, 360, and 480 minutes after the herbicides application. A control treatment without herbicide application was added. Visual evaluations of control plants were taken at 7; 14; 21 and 28 days after application and at the end the dry mass of plants was determined. The rain occurrence after 15 minutes of application of glyphosate formulations Roundup Transorb, Roundup Transorb R and Roundup Ultra did not affect the control efficiency on plants of S. obtusifolia. For formulations of Roundup Original and Roundup WG and, 2,4-D it was necessary a 30 minutes period without rain for an efficient control of weed.
Highlights
Senna obtusifolia (L), known locally as fedegoso, occurs quite commonly in cultivated areas in Brazil and is the cause of problems for major crops
At the first evaluation, carried out at 7 days after application (DAA), it was seen that all the chemical treatments resulted in damage to the plants of S. obtusifolia, irrespective of the occurrence of rainfall after application; but only the treatment employing application of glyphosate as the Roundup WG formulation and that with glufosinateammonium provided satisfactory control of the weed; over 80% control, with rainfall six and four hours after application respectively (Table 1)
Similar results were found by Barnes and Oliver (2003), who observed control percentages above 80% for plants of S. obtusifolia submitted to glyphosate application at 7 DAA, but without further rainfall
Summary
Senna obtusifolia (L), known locally as fedegoso, occurs quite commonly in cultivated areas in Brazil and is the cause of problems for major crops This species, which is probably native to the Americas, is widely dispersed over tropical and subtropical regions of the world, including Brazil, where it is found in all regions (KISSMANN; GROTH, 1999). It is an aggressive, highly-prolific plant, having large seeds and showing low sensitivity to most herbicides used in the cultivation of sugar cane (LORENZI, 2006; RODRIGUES; ALMEIDA, 2005). Cruz et al (2009), when quantifying the population-density levels of weed species in rotated crops of soybean, corn and rice in the cerrado region of the Brazilian state of Roraima, verified the presence of 4,333 plants of S. obtusifolia per hectare
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