Abstract
Cultivation of the cowpea is important in various regions of Brazil, but competition from weeds is one of the factors which limit productivity. The aim of this study therefore was to evaluate the pre-plant selectivity and efficiency of different herbicides, and combinations of herbicides, in the cowpea [Vigna unguiculata (L.) Walp.]. An experiment was carried out in a randomised block design, in lots split over time and with three replications, using a 4 x 7 factorial scheme, where the treatments consisted of: glyphosate, glyphosate + imazethapyr, glyphosate + flumioxazin, glyphosate + imazethapyr + flumioxazin, glyphosate + ready mix (imazethapyr & flumioxazin), and two control treatments (one with no weeding and one with manual weeding). The treatments were evaluated in combination with four different sowing times, i.e. immediately after application of the herbicides, and at five, ten and fifteen days after application (DAA). The combination of glyphosate + flumioxazin at 15 DAA, gave the highest mean productivity, 1,105.32 kg ha-1, followed by manual weeding with 1,027.37 kg ha-1. The herbicide mixtures of glyphosate + imazethapyr + flumioxazin caused phyto-toxicity in the cowpea crop, limiting the production components. The best strategies for weed control in this crop are manual weeding with seeding at 10 DAA, as well as the application of a glyphosate + flumioxazin mixture with seeding at 15 DAA.
Highlights
The cowpea [Vigna unguiculata (L.) Walp.] is a species of great importance for human consumption due to its nutritional value
It can be seen that the treatments glyphosate + imazethapyr (T4) and glyphosate + imazethapyr + flumioxazin (T6), with sowing carried out 15 and 10 days after application (DAA) respectively, were not effective in controlling the weeds, even when compared to the control with no weeding (T1)
Given that there are various factors which can affect the efficiency of herbicides, a reduction in the efficiency of these products may have been caused by the physicochemical properties or factors related to the technology of applying the two mixtures, or the characteristics of soil and climate at the experimental site
Summary
The cowpea [Vigna unguiculata (L.) Walp.] is a species of great importance for human consumption due to its nutritional value. It is a good source of protein (on average 23 to 25%). Interference from weeds is an important factor, and should be taken into account in cultivating the cowpea. Some farmers neglect such control, which impairs the mean productivity of the crop, since, as reported in the literature, this interference may result in a significant reduction in grain yield (FREITAS et al, 2009; OLIVEIRA et al, 2010; VIDAL et al, 2008). With expansion of the areas cultivated with cowpea, manual weeding has changed from being the main method, to complementing methods of chemical control. With expansion of the areas cultivated with cowpea, manual weeding has changed from being the main method, to complementing methods of chemical control. Silva, Vivian and Oliveira Junior (2007) report several advantages in using herbicides for weed control, such as being less labor-dependent, being efficient even during rainy periods, properly controlling weeds in the crop row, not damaging the root system of the crop, making it possible to use minimum tillage or direct planting, and being efficient in preventing vegetative propagation
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