THE IMPACT OF HERBICIDES ON THE INCIDENCE AND DEVELOPMENT OF RHIZOCTONIA SOLANI-INDUCED COTTON SEEDLING DAMPING-OFF

The impact of three pre-plant herbicides, trifluralin, pendimethalin a nd prometryn, on the incidence and the development of Rhizoctonia sola ni-induced cotton seedling damping-off was investigated in the control led environmental chamber and in the field. In the controlled environm ental chamber experiments, trifluralin, pendimethalin and prometryn we re applied to the soil at 1.8, 2.4, and 3.6 mu g a.i. g(-1) soil, resp ectively (equivalent to the respective recommended field concentration s of 0.7, 0.9, and 1.3 kg a.i. ha(-1)). In the controlled environmenta l chamber experiments, where soil was infested at planting, applicatio n of prometryn, but not pendimethalin or trifluralin, to the soil caus ed a significant (P < 0.05) increase in damping-off incidence. In cont rolled environmental chamber experiments where soil was infested after emergence, damping-off increased significantly (P < 0.05) in the pres ence of pendimethalin and prometryn, but not trifluralin. In a field e xperiment conducted in Safford, Arizona, pre-plant application of pend imethalin or prometryn, but not trifluralin, caused significant (P < 0 .05) increases in disease incidence. In another field experiment in Tu cson, Arizona, a significant (P < 0.05) increase in disease incidence was observed in plots treated with prometryn, but not in plots treated with pendimethalin or trifluralin. In both controlled environmental c hamber and field experiments, application of selected herbicides had s ignificant effects on disease development as judged by the slope of di sease progress curves.