The effects of cotton and soybean selective herbicides on mycellial growth of Rhizoctonia solani causal agent of damping off

This investigation was conducted to evaluate the effect of herbicides trifluralin, ethalfluralin, alachlor and metribuzin on mycellial growth of Rhizoctonia solani anastomosis group 4, the causal agent of cotton and soybean damping off. The experiments were carried out in 2011 at Department of Weed Research, Iranian Research Institute of Plant Protection, Tehran. At first stage, growth reaction of the fungal colonies to the herbicides on PDA was studied. Then, this reaction to discs contaminated with the herbicides, compared with not using herbicide control, in two series of experiments was investigated. The results of high concentration of herbicides in PDA indicated that growth of the fungal colonies on PDA containing trifluralin at 12500 or 25000 ppm, ethalfluralin at 17500 or 35000 ppm, alachlor at 20000 or 40000 ppm was completely inhibited. R. solani growth on PDA containing metribuzin at 2500 or 5000 ppm was not completely inhibited, but this treatments, compared with control, significant reduced mycellial growth of the pathogen. The experiment at lower concentrations of the herbicides showed that alachlor, trifluralin and ethalfluralin, resprctively at 509, 318 and 445 ppm, significantly reduced the colonies growth. Among the recent treatments, the effect of alachlor was significantly more than the others. Paper discs contaminated with herbicides at three different concentration, showed no evidence of their effect on mycellial growth of the pathogen.