The aim of this study was carried out in order to determine effect on the species, dry weight, density, frequency and similarity ratio of weeds in winter, freeze and summer wheat varieties. This research was conducted in Agricultural Research and Extension Center of Agricultural Faculty of Ataturk University, in dryland conditions in 2005-06 and 2006-07 cropping seasons. Weeds were eveluated as sources of plant material and collected from plots where facultative eleven bread wheat cultivars sown as winter, freezing and spring. The experimental design was a randomized block in a split-plot configuration with three replications. In this study, three different sowing times (winter sowing, freezing sowing and spring sowing) and eleven bread wheat cultivars were used, with sowing times as main plots and wheat cultivars randomized as subplots. Each block consisted of six rows spaced 20 cm apart (1.2 m) and row length of 6.0 m with 33 plots. In the experiment area 48 different weeds covered 43 species in 19 families were determined. Density of the weed changed between 1 and 181 plant/m(2) and average density of the weed was determined as 14.27 plant/m(2). According to ANOVA, different between wheat varieties in terms of effect dry weight of weed was statistically important (P<0.001). The most values on density of the weed were found out Cirsium arvense (L.) Scop. (canada thistle) (2.64 plant/m(2)), Convolvulus arvensis L. (field bindweed) (1.79 plant/m(2)) and Geranium tuberosum L. (tuberous geranium) (0.58 plant/m2) in winter wheat; C. arvensis (2.36 plant/m(2)), Lactuca serriola L. (oil lettuce) (1.76 plant/m(2)) and C. arvense (1.36 plant/m(2)) in freeze wheat; Amaranthus retroflexus L. (redroot pigweed) (5.48 plant/m(2)), Sideritis montana L. (field iron wort) (2.12 plant/m(2)) and C. arvense (2.06 plant/m(2)), in summer wheat; respectively. The most values on frequency of the weed were found out C. arvense (78.79%), Adonis aestivalis L. (rose a ruby) (63.64%) and C. arvensis (39.39%) in winter wheat; L. serriola (66.67%), C. arvensis (60.61%) and C. arvense (45.45%) in freeze wheat; L. serriola (63.64%), C. arvensis (57.58%) and S. montana (51.52%) in summer wheat; respectively. Also, in similarity ratio diversities were determined. As a result, Aksel-2000 in winter and freeze wheat, and Uzunyayla in summer wheat were found out stronger than others varieties opposite to weed competition.