Estimating yield loss of faba bean ( Vicia faba L.) caused by gall disease in north Shoa, Ethiopia

Faba bean is the most important food legume crop; however, its productivity is threatened by faba bean gall (FBG) disease. Faba bean gall is an emerging and destructive disease in the highlands of Ethiopia. Field experiments were conducted on farmers’ field during the 2018 and 2019 cropping seasons in Bassona Worana district, Ethiopia under natural conditions to estimate yield losses on local cultivar and improved faba bean varieties and to determine fungicides spray schedules. The experiments consisted of two moderately tolerant (Degaga and Gora) faba bean varieties and one susceptible local cultivar, two fungicides [Bayleton 25 WP (Triadimefon 250 g kg −1 ) and Ridomil Gold MZ 68 WG (Metalaxyl 40 + Mancozeb 640 g kg −1 )] and two application schedules (10 and 15 days). The treatments were arranged in randomized complete block design with three replications in factorial combinations. The results showed that use of different faba bean genotypes and applications of fungicides significantly ( P  < 0.001) reduced FBG disease epidemics and minimized grain yield loss. Variety Gora sprayed with Bayleton at 10 days interval recorded low mean FBG disease severity (26.7 and 13.0%) and AUDPC of 1866.7 and 751.7%-days in 2018 and 2019, respectively. High mean grain yields of 3.7 t ha −1 (2018) and 5.0 t ha −1 (2019) were also obtained from variety Gora sprayed with Bayleton at 10 days interval. High grain yield losses of 62.5% (Degaga), 54.1% (local cultivar) and 50.0% (Gora) were obtained from unsprayed plots of each genotype. Conversely, faba bean genotypes obtained yield increases of 166.4% (Degaga), 100% (Gora) and 121.3% (local cultivar) when treated with Bayleton at 10 days interval in 2018. Similar trends were observed regarding 100-seed weight (HSW) loss and in 2019. Moreover, unsprayed plots of each genotype recorded the highest disease severity and AUDPC and the lowest grain yield in both cropping years. On the other hand, faba bean grain yield and yield components demonstrated an inverse relationship with disease severity. Hence, use of tolerant faba bean varieties like Gora and application Bayleton at a rate of 0.7 kg ha −1 at 10 days interval is essential to manage FBG disease, thereby minimizing yield and HSW losses of faba bean in the study areas.