Assessment of Indigenous Weed Species and Their Agronomic Importance in Ogun State Croplands

This study assesses the diversity, density, and agronomic importance of indigenous weed species in crop fields in Ogun State, South West Nigeria. Understanding weed community composition is essential for designing effective, cost-efficient weed management programmes that target the most economically damaging species without unnecessary use of broad-spectrum herbicides. Ogun State's diverse farming systems encompassing cassava, maize, vegetable, and mixed cropping create varied weed ecological niches that support diverse weed communities. This study uses systematic weed surveys of 90 farm plots across Abeokuta South, Ijebu North, and Remo North local government areas using quadrat sampling method at three, six, and nine weeks after planting across two cropping seasons. Weed species are identified botanically, and density, frequency, relative abundance, and importance value index are computed for each species. Economic threshold assessments are conducted for the dominant species. Findings reveal 48 weed species from 22 families across the surveyed fields, with Digitaria horizontalis, Euphorbia heterophylla, Chromolaena odorata, and Commelina benghalensis showing the highest importance value indices. Annual broadleaf weeds dominate maize fields while perennial grass weeds are more prevalent in cassava. Weed density peaks at six weeks after planting across all crops. The study concludes that targeted management of the top five dominant species using their identified critical periods provides the most cost-effective weed management framework. It recommends community-level weed surveys as a basis for locally specific extension guidance.

Keywords: weed survey, weed diversity, importance value index, Ogun State, weed management.