Fungicidal management of the newly emerging faba bean disease “gall” (Olpidium viciae Kusano) in Tigray, Ethiopia

Faba bean (Vicia faba L.) is by far the most important legume in Ethiopia and the most important single subsistence crop after the staple cereals. However, its production is constrained by biotic and abiotic stresses. Among the biotic constraints, the emerging faba bean gall disease, caused by Olpidium viciae, is the major and most destructive disease in regions where faba bean is grown. Field experiments were conducted at two locations to evaluate the efficacy and application frequency of fungicides that effectively and efficiently control faba bean gall disease. Four fungicides: Baylaton 25 WP, Ridomil Gold MZ 68 WG, Mancozeb 80% WP (each 2-4 sprays), and Aster (liquid copper fungicide) with 2-5 sprays, and combination of Aster and the former three fungicides were tested along cultural practices in three replications using a randomized block design. The results revealed that the use of Baylaton 25 WP and Ridomil Gold MZ 68 WG was significantly (P < .05) reduce faba bean gall explained by the lower area under disease progress curve (AUDPC), percentage severity index(PSI) and incidence of the disease as well as higher yield at both locations. The application of Baylaton 25 WP and Ridomil Gold MZ 68 WG with all sprays (2-4) reduced the AUDPC by at least by 1288.7%/day and 1187%/day in Ofla (Menkere) and 369.2%/day and 364.2%/day in Enda-Mekoni (Mekhan) compared to control/unsprayed, respectively. The yield advantage of the two fungicides compared to control was 68.5% and 46.1% (in Ofla) and 24.9% and 32.5% (in Enda-Mekoni), respectively. The biomass and grain yield of faba bean showed significant difference (p < .05) and negative correlation with AUDPC and PSI. This indicated that the PSI and AUDPC were very important in determining the extent of losses in yield and yield components. AUDPC of the disease had a perfect positive correlation (r = 0.99 in Ofla and r = 0.96 in Enda-Mekoni) with PSI ascertained that linear interaction. The use of recommended rate of Baylaton 25 WP (0.3 kg ha-1) and Ridomil Gold MZ 68 WG (2.5 kg ha-1) with 2-3 sprays at 10-day intervals could effectively control faba bean gall depending on its intensity and weather conditions. Integrating of the effective fungicides with other management options like host plant resistance could reduce the application frequency and more economically feasible.