The effect of the application of different rates of herbicides on the residual level of the herbicides and their metabolites in harvested maize cobs
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Abstract
Background: The use of herbicide in weed control has grown significantly in Nigeria in recent years. Most of the applications are indiscriminately carried out by illiterate farmers, and therefore pose a significant threat to the environment, crop yield and human health. This study assessed the effects of different application rates of the herbicides on the residual levels of the herbicides and their metabolites in harvested maize cobs.
Methods: The study was carried out in a plot of land at the University of Port Harcourt in 2013 and 2014, using a randomised complete block design with three replicates, and plot size of 2 m × 2 m. N-(phosphonomethyl) glycine was used to prepare the experimental plots, while different application doses of Primextra dual gold (2-chloro-4-(ethylamino)-6-isopropylamino-1,3-5-triazine and 2-chloro-N-(ethy-6-methy(phenyl)-N-(2-methoxyl-1-methylethyl acetamide) were applied to the plots, after planting the maize. The control plot was not treated with the herbicides. The residual levels of the herbicides and their metabolites in the cobs harvested from the plots were tested using gas chromatography, with Pulsed Flame Photometric Detector.
Results: The residue of the herbicides and their metabolites were barely detectable in the harvested maize cobs when the herbicides were applied at or below their recommended dose, but noted at up to 0.09 ppm, when applied at twice the recommended dose. The residues were also noted in some of the cobs harvested from the control plot, at a mean concentration of 0.0033 ppm, which is significantly <0.012 ppm recorded in the treated plot.
Conclusion: The residual concentrations of herbicides and their metabolites in harvested crops increased with increasing application dose of the herbicides. Proper education of farmers is, therefore, needed to safeguard the environment and public health.
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