The Effect of Tree Spacing and Land Use History on Managing Wattle Rust Disease of Acacia mearnsii in Northwestern Ethiopia

Abstract

Wattle rust disease, caused by Uromycladium acaciae, has emerged as a critical challenge to Acacia mearnsii in the Awi Zone of northwestern Ethiopia. This study examined the effect of tree spacing and land use history on disease incidence and severity, and explored local perceptions of management practices. A randomised complete block design (RCBD) with three spacing treatments (0.5 × 0.5, 1 × 1, 1.5 × 1.5 m) was implemented across three districts—Fagita Lekoma, Ankasha Guagusa, and Banja Shekudad in 2021. Additionally, disease occurrence in three-year-old plantations (common spacing: ~0.5 × 0.5 m) on cropland, grazing land, and plantation land was assessed. Community knowledge and preferences for disease management were gathered through structured surveys and focus group discussions with 150 respondents, including both farmers and forest administrators. The findings revealed that wider spacing (1.5 × 1.5 m) significantly reduced disease incidence by up to 54.87% and severity by 45.74% compared to narrow spacing (0.5 × 0.5 m). Trees planted on cropland exhibited significantly lower disease levels compared to those on grazing or plantation land. Local farmers favoured integrated practices such as increased spacing, sanitation pruning, tilling, weeding, and intercropping with cereals, which align with scientific evidence on disease suppression through microclimate modification and improved soil health. Adopting a 1.5 × 1.5 m planting spacing and prioritising post-cropland areas are recommended for new plantations in disease-prone districts. Further research should explore disease-resistant varieties, species diversification strategies, and closer spacing (< 0.5 × 0.5 m), which are currently practised by some smallholders, to further enhance disease management and inform extension programmes.