Wild barley species, including wild barley (Hordeum spon-taneum Koch.), mouse barley (Hordeum murinum L.), smooth barley (Hordeum glaucum Steud.), and Hordeum distichon L., have been reported as troublesome grass weeds in the irrigated wheat farms of Iran (Montazeri et al . 2005). In different regions of Iran, Hordeum spontaneum Koch. (Wild barley) become a noxious weed in wheat fields. Sulfosulfuron (Apyros 75 WG) is an effective herbicide for control of this weed, but its efficacy may depend on weed phenological stage. Sulfosulfuron is a sulfonylurea herbicide developed for the selective control of broad-leaved weeds and grass weeds in wheat (Parrish et al . 1995). Pot experiments were carried out in natural conditions in Agronomy & Plant Breeding Department of University of Tehran, Karaj, in 2012 to study the best application timing and dose of sulfosulfuron. The experimental was Randomized Complete Block Design with four replications in which treatments were arranged as factorial. The first factor was eight doses of sulfosulfuron including 0 (control), 10.1, 20.2, 30.3, 40.5, 50.6, 60.7, and 70.8 g a.i. ha-1, and the second factor was sulfosulfuron applying doses in three growth stages of H. spontaneum (2-3 leaves, tillering and second node). Results indicated that application of 20.2 g a.i. ha-1 of sulfosulfuron in second node stage had the best efficacy in controlling the H. spontaneum without any plant recovery. H. spontaneum was recovered when recommended herbicide doses were applied at two- to three-leaf and tillering stages. Although increasing the sulfosulfuron dose from 50.6 up to 70.8 g a.i. ha-1 led to plant death. Overall, it was concluded that application of sulfosulfuron at early stage of 2-3 leaves results in an increase in dose of herbicide or re-spraying. Acceptable result would be achieved by application of sulfosulfuron at 20.2 g a.i. ha-1 in second node.
