ABSTRACT
Weeds are worldwide in distribution. They are traced at different intensities in all agroecosystems of the world. The infestation of weed species differs enormously based on geographic location, season, weather pattern, soil type and its fertility status, crop species, its growth stage, and agronomic practices adopted by farmers. There are indeed several families of plants that behave as weeds in cropping expanses. At times volunteers from previous crop too become weeds. This situation is common in notillage plots. The weed flora in a crop field is often dynamic. The weed species that become dominant at different times and their potential to thwart crop growth needs to be understood properly. Weeds are no doubt part of a cropping expanse. They need to be controlled, if not, they divert significant quantities soil nutrients and moisture. Weeds could be deep rooted. Weed roots compete for underground soil space, nutrients and water with crop plants growing closely. They are often fast growing and in such situations weeds compete and intercept photosynthetic radiation. Weeds may reduce photosynthetic light reaching the crop canopy and therefore reduce biomass formation. Weeds multiply rapidly. The crop stage at which weeds become rampant seems important. Weeding at early stages of crop is most effective. The intensity and species of weeds flourishing in a field and the crop species are factors that affect biomass and grain/forage production.
