دوره بحراني كنترل علفهاي هرز توتون ( NICOTIANA TABACUM L) در شرايط استان گيلان

Critical Period of Weed Control in Tobacco (Nicotiana tobucum L.) in Guilan Province

To determine the critical period of weed control in tobacco, an experiment was conducted in Tobacco Research Institute of Rasht in 2005. The experiment was conducted using a randomized complete block design with three replications and 12treatments of hand weedings in twosets. The first set of treatments included weed infested periods of 0, 10,30,50,70, and85days after tobacco transplantation (OAT) and the second set oftreatments included weed free periods of 0, 10, 30, 50, 70. and 85 days. These two sets of treatments were fitted to Logistic and Gompertz functions to determine thecritical period of weed control. Crop height, number of leaves, cropyield, thenumber and weight of weeds in a square meter of each plot before harvesting were also determined. The most dominant weeds of the field were Purple nutsedge tCyperus rotandus L.), Large crabgrass (Digitana sanguinalis L.), Yellow foxtail (Setaria gluuca L.), Bcrmudagrass (Cyndon dactylon (L,) Pers). anti Redroct Pigweed (Amarantus retrcflesus L.). Increasing the periods of controlling weed infestation reduced thenumber of weeds and created a better condition for tobacco growth.Critical periods of weed conlrul between 27 and SODAT and between 23 and 59 DAT were found as suitable.while allowing 10ʹ% and 5% acceptable yield reduction, respectively. A positive relation was observed between controlling weeds within critical the period of weed control and plant height as well fLS number of leaves. By increasing weed free periods, plant height, and the number of leaves wen: increased.