Comparative Performance of Raptor and Iris Herbicides on Weed Suppression and Grain Yield of Cowpea in Two Agro-Ecological Zones of Nigeria

Abstract

A field experiment was conducted during the 2021 rainy season to evaluate the performance of two post-emergence herbicides, Raptor and Iris, on weed suppression and grain yield of cowpea (Vigna unguiculata (L.) Walp.) in the Sudan and Northern Guinea savannas of Nigeria. The study was carried out at the Teaching and Research Farm, Bayero University, Kano (Sudan savanna) and the International Institute of Tropical Agriculture (IITA) research station, Zaria (Northern Guinea savanna). Treatments consisted of two cowpea varieties (IT99K-573-1-1 and UAM14-122-17-7), three application rates of Raptor (1.5, 1.0 and 0.5 L ha⁻¹), three application rates of Iris (0.8, 0.6 and 0.4 L ha⁻¹), hoe weeding, and a no-weeding control. The treatments were arranged in a split-plot design with three replications. Data were collected on weed cover, weed density, weed biomass, weed control efficiency, phytotoxicity, phenological traits, and grain yield.
Results showed that weed control methods significantly influenced weed suppression and grain yield at both locations. Hoe weeding and Raptor, particularly at 1.5 and 1.0 L ha⁻¹, consistently recorded lower weed density, higher weed control efficiency, and superior grain yield compared to Iris treatments and the unweeded control. Iris herbicide, especially at higher application rates, caused significant phytotoxic effects on cowpea plants at the Sudan savanna location, leading to delayed flowering and reduced yield. Grain yield was highest under Raptor at 1.5 L ha⁻¹ at Kano and Raptor at 1.0 L ha⁻¹ at Zaria. The performance of the cowpea varieties varied across locations, with IT99K-573-1-1 performing better at Kano and UAM14-122-17-7 showing superior performance at Zaria.
The study concludes that Raptor herbicide is more effective and safer than Iris for post-emergence weed control in cowpea across both agro-ecological zones. Application of Raptor at 0.5 L ha⁻¹ in the Sudan savanna and 1.0 L ha⁻¹ in the Northern Guinea savanna is recommended for effective weed suppression, reduced phytotoxicity, and improved grain yield.