Critical Period of Weed Damage in Peanut (Arachis hypogaea L.) in Sari

In order to determine the critical period of weed damage in peanut a field experiment was laid out based on randomized complete block design (RCBD) with three replications in 2012. Treatments consisted of two series of weed interference and weed-free periods of 15، 30، 45، 60 and 75 days after planting of peanut. Full-season control of weeds and full-season interference of weeds were also included as control treatments. Seed yield was affected significantly by control and weed-free treatments. Increasing of weed interference periods decreased peanut seed yield، while increasing of weed control periods increased peanut seed yield. Mean comparisons showed that the highest (2100 kg. ha-1) and lowest (294 kg. ha-1) of peanut yield observed at full season weed-free and 75 days weed interference after planting، respectively. Full-season weeds interference reduced peanut yield by 81% compared with full season weed-free plots. Beginning and end of the critical period of weed damage were determined by Gompertz and Logistic equations with high accuracy (R2=0. 96 and R2=0. 95، respectively). Based on 5، 10 and 15% acceptable seed yield losses، the critical period of weed control were 9 to 76، 12 to 63 and 16 to 54 days after planting at Sari condition.