A preliminary weed survey of citrus orchard and nursery was conducted in National Horticultural Research Institute (NIHORT) Ibadan in the wet season of 2009. The result showed that out of 54 weed species encountered during the survey 39 were broadleaf weeds, 13 were grasses and two were sedges. The main citrus orchard recorded 55% of the total weed species while the citrus organic orchard recorded the least (27.8%). Seven different weed species were propenderant with high Relative Frequencies covering over 5% of the total weed species in three locations (citrus organic orchard, citrus/vegetable intercrop plot and juvenile citrus plot). Out of these, 3 weed species: Ageratum conyzoides L, Imperata cylindrica L. Raeuschel and Tridax procumbens L. had the greatest Relative Frequency of 12% each, in citrus organic orchard. However, the rest sampled areas have between 4 and 6 weed species accounting for 5% or more showing the whole survey area to be very rich in flora. Tridax procumbens L. and Chromolaena odorata (L) R.M Kings and Robinson associated with all the citrus based cropping systems in all the locations. Relative density of Euphorbia heterophylla L (35.95%) in juvenile citrus orchard was higher than any other species in all the locations. Panicum maximum had the highest Relative Density (18.8%) in citrus main orchard among the grass weed species next to Imperata cylindrica L. Raeuschel (25.09%) in citrus organic orchard indicating a higher infestation of citrus orchard than other species.