Assessment of weed species composition and species diversity in some fruit orchards

Fruits are often perennial crops and therefore can be invaded by weeds at many different times of the year because of their varied life-cycle. Thus a weed survey was conducted in some fruit orchards containing guava/soursop, mango, irvingia and plantain/banana at the National Horticultural Research Institute (NIHORT) Ibadan in 2009 cropping season to determine weed species composition and species diversity. Weeds were sampled from each fruit orchard with a 0.5m × 0.5m wooden quadrat, identified to species level, counted and recorded. Data collected were used to calculate relative frequency, relative density and importance relative value for each species. Result shows that 45 weed species were encountered in all the fruit orchards and mango orchard had the highest species diversity (33 species) while the least was recorded in guava/soursop orchard (10 species). All these 10 species had their relative frequencies 5% out of which Ageratum conyzoides Panicum maximum Cyperus esculentus Chromolaena odorata Commelina erecta are of ecological importance. Three weed species: Ageratum conyzoides, Centrosema pubescens and Panicum maximum associated with all the fruit orchards in all the locations and T. procumbens was the most abundant and most dominant species in guava/soursop, irvingia and plantain/banana orchards while Echinocloa phyllopogon followed the same trend in mango orchard. These weeds are low-growing plants and regular weeding before seed formation will help to reduce their abundance in these orchards so that they do not interfere with harvesting of these fruits.