A Study on Reduced Dosages Effect of Imazethapyr at Different Phenology Stages of Soybean (Glycine max) on Cocklebur (Xanthium strumarium)

A factorial experiment was conducted based on randomized complete block design with four replications in order to investigate of the effect of reduced dosages of imazethapyr at various growth stages of soybean on cocklebur at Mahdasht، Karaj during 2009-10. The evaluated experimental factors were included five levels of imazethapyr dosage (0، 25، 50، 75 and 100 g a. i. ha-1) and soybean phenological growth stage in three stages (two، three and four-leaved stage). The Fitting of experimental data by the logistic equations showed that the imazethapyr application at two-leaved stage of soybean had the highest effect on the reduction of shoot dry weight، height، number of axillary branch and seed dry weight of cocklebur. Using 9. 89 g a. i. ha-1 imazethapyr at two-leaved stage of soybean led to a 50% reduction in dry weight of cocklebur. This reduction amount at 3 and 4-leaved stages of soybean were obtained by imazethapyr application in the dosages of 42. 84 and 61. 67 g a. i. ha-1، respectively. Moreover، the results showed that any significant difference was observed between 75 and 100 g ai. ha-1 of for imazethapyr in the cocklebur control. Therefore، the application of reduced dose of 75 g a. i. ha-1 can suitably control cocklebur at two-leaved stage of soybean. The highest yield of soybean (3327 kg ha-1) was also achieved by imazethapyr application during the two-leaved growth stage.