Critical Period of Weed Control in Cumin (Cuminum cyminum) under Rain-Fed Conditionin in Sabzevar

The critical period of weed control in cumin (Cuminum cyminum) were determined by field study in 2011 in Sabzevar. Experiment was conducted in randomized complete block design with 3 replications. Treatments were weeding at 15, 30, 45and 60 days after emergence during the growing season (weed free), and 15, 30, 45and 60 days without weeding (weed infested) in the growing season and includes free of weed and weed infested in the entire growing season. Beginning and end of the critical period of weed damage were determined by Gompertz and Logistic equations. The results showed that weed dry weight was significantly increased with increasing duration of infection and reduce weed-free period. Full-season weeds interference reduced plant height (11.29%), number of lateral branches (39.14%), number of umbels (46.87%), number of seeds per umbrella (43.12%), seed yield (48.99%), biological yield (48.99%) and essential oil yield (26.94%) compared full season weed-free plots, respectively. Based on 5 and 10% acceptable seed yield losses, the critical period of weed control was 9-76 and 12- 63 days after planting at rain-fed condition.