Root Rot Disease in Association with Common Bean Stem Maggot (Ophyiomia phaseoli) and Evaluation of Insecticides for Management of Stem Maggot on Common Bean (Phaseolus vulgaris L.) at West Hararghe, Ethiopia

Abstract

Bean stem maggot (BSM) and root rot disease are economically important pests of common beans. The wounds caused by BSM feeding act as entry points for root rot-causing pathogens. The objective of this paper was to assess root rot disease associated with stem maggots and evaluate insecticides for managing stem maggots on common beans in west Hararghe, Ethiopia. This study included a two-part survey and field experiment. The survey was conducted at different common bean growing agro-ecologies of the west Hararghe zone, namely, the Oda Bultum, Habro, and Chiro districts, while the field experiment was conducted at the Habro district, Bareda, Oda bultum University farm site. Twenty farms in four kebeles were randomly selected for each district to determine the occurrence and incidence of bean root rot and bean stem maggot alone and their interactions. Each bean root was examined for the presence of bean stem maggot and root rot disease-causing pathogens. The results showed that the occurrence and incidence of bean root rot diseases and bean stem maggots were significant (p<0.05) in the surveyed areas. Rhizoctonia solani, Pythium spp.and Fusarium spp. were the major root rot pathogens isolated. Ophyiomia phaseoli was the dominant bean stem maggot in the surveyed districts. The incidence of common bean fly and root rot computed was significantly different (P< 0.05) among the surveyed districts. The highest disease and bean fly interaction incidence (50.85%) was obtained from the Chiro district, followed by the Habro district (36.04%). The lowest incidence of disease and bean fly interaction (26.97%) was recorded in the Oda Bultum district. For the field experiment, six different insecticides, namely, confidor SL 200, Karate 5% EC, Dimeto 40% EC, Alpha guard, Apron star 42 WS, and Bravo 5% EC (W/V), were evaluated and compared to the control, which was not sprayed to determine the differences among insecticides. Common bean agronomic parameters showed significant differences (P< 0.0001 to 0.05) among the treatments compared to those of the control. The grain yield ranged from 1095 to 2950 kg/ha among the treatments. The addition of Confidor SL 200, followed by Apron Star 42 WS and dimethoate (40%) significantly reduced the number of bean stem maggots and increased common bean agronomic yield and yield component parameters.