In order to investigate the possibility of reducing herbicide usage in combination with plant density and planting pattern, a field experiment was designed in Chenaran, Khorasan Razavi, on 2010. The experiment was split plot treatments based on RCBD with three replications in factorial arragement. The treatments included of 3 level of plant density (100000, 120000 and 140000 plants ha-1) and 2 level of planting pattern (single and double row) as a main plot and Nicosulfuron dosage at four levels[(0), 50% recommended dose (1 l ha-1 ), 75% recommended dose (1.5 l ha-1) and 100% recommended dose (2 l ha-1)] as a sub-plots. The control plots consisted of weedy control and weed free check, respectively. Sampling was done to measure weed density, total dry matter and evaluating herbicide effect on weeds according to the EWRC 20 days after the corn emergence and repeated every 20 days. Corn silage yield was increased due to reduction of double row planting pattern and increasing of planting density significantly in dough seed stage. The results also showed that reduction of the weed density and total dry matter of weeds and desirable weed controls at first stage after the herbicide treatments. Experimental treatments had also a significant effect on weed species diversity according to shannon- winer index,sensitive population such as common purslane (Portulaca oleracea L.), buckhorn plantain(Plantago lanceolata L.), prostrate knotweed (Polygonum aviculare L.), black nightshade (Solanum nigrum L.) and Johnson grass (Sorghum halepens L.) was reduced and according to simpson diversity index, low population such as redroot pigweed (Amaranthus retroflexus L.),common lambsquarters (Chenopodium album L.), field bindweed (Convolvulus arvensis L.) and Canada thistle (Circum arvensis L.) by the end of growth season.