VIEW ARTICLE

Effect of the Herbicide Diphenamid on Damping-off Disease of Pepper and Tomato. J. Katan, Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot, Israel; Y. Eshel, Department of Field and Vegetable Crops, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot, Israel. Phytopathology 64:1186-1192. Accepted for publication 5 April 1974. DOI: 10.1094/Phyto-64-1186.

Rhizoctonia solani was the major causal organism for damping-off in directly seeded pepper (Capsicum frutescens) fields. The effect of the herbicide diphenamid on the incidence of this disease was tested by sowing peppers in soil inoculated with R. solani at various inoculum concns. With each tested isolate, diphenamid increased Rhizoctonia damping-off disease at least at one inoculum concn. This disease increase was not observed, however, in separate experiments carried out with Pythium. Results were variable for tomatoes inoculated with R. solani. The possible mechanisms involved in the increase in Rhizoctonia disease of pepper were studied by analyzing the effects of the herbicide on the pathogen, the host, and soil microorganisms. Diphenamid is slightly toxic to the pathogen and does not stimulate its growth in vitro, its respiration and glucose utilization is sterile soil, or its virulence to pepper. Pepper seedling resistance to R. solani was not affected by pretreatment with diphenamid. The herbicide enhanced colonization of bean stem segments by R. solani in natural soil, and suppressed soil microorganism respiration and glucose utilization in glucose-amended soil. Diphenamid also slowed down the decrease in time of R. solani colonization and disease incidence. It is suggested that suppression of soil microorganisms contributed to the disease increase in pepper. In contrast with pepper, pretreatment with diphenamid increased tomato seedling resistance to R. solani.