The weeds of a pistachio orchard such as lambsquarters (Chenopodium album), camelthorns (Alhagi camelerum), hoary cress (Cardaria draba), orchardgrass (Dactylis glomerata), downy brome (Bromus tectorum), bind weed (Convolvulus arvensis), velvet leaf (Abotilon teophrasti), Russian thistle (Salsola kali), kochia (Kochia scoparin), black nightshade (Solanum nigrum), Mesquite bean (Prosopis sp.), continue to be a significant problem in pistachio orchards. In 1999, three trials were carried out in Iran, to assess the herbicidal activity and selectivity of urea in mixture with yolk, instead of herbicides for weed control in pistachio orchards. A randomized complete block design with 4 replications was followed up and sprayed. Data of different treatments for weed control and injury were recorded. Combination treatment of 24 per cent urea and 6 per cent yolk gave excellent control of lambsquarters, camelthorn (green part only), hoary cress, orchardgrass, downy brome, bind weed, velvet leaf, Russian thistle, kochia and black nightshade.