Herbicide weed control – induced differential tolerance and productivity in cowpea plants

Abstract

The use of herbicides is a represents an efficient way to control the infesting plant population, since it is associated with low operational cost, and it does not demand large amounts of labour. An obstacle to growing cowpea (Vigna unguiculate) is the absence of herbicides registered for this crop. The objective of this work was to evaluate the tolerance of cowpea to herbicides. The experiment was carried out in a randomised block with treatment controls with and without weeding, Bentazon (720 g ha^-1), Fluazifop-p-butyl (250 g ha^-1), Fomesafen and a tank mix between Fluazifop-p-butyl + Fomesafen (250 + 187.5 g ha^-1) with treatment replicates. The herbicides were applied on vegetative (V3 – stage) cowpea plants using a CO₂-pressurised backpack sprayer with four spray tips TT 110.02 operating at a pressure of 2.5 bar and applying 240 litres of syrup per hectare. The cultivar BRS Guariba, with five planting lines per plot, was tested with the three central lines of the useful area, scoring 0.5 m of the ends. The species Oxalis latifolia was difficult to control. The Fluazifop-p-butyl + Fomesafen mixture presented better control of weeds. The herbicides caused phytotoxicity to cowpea and reduced leaf area and dry mass. The productivity of the crop was affected due to the low control of weeds. It was concluded that the cowpea presented differential tolerance to the herbicides tested doses.