Agronomic Performance and Economics of Yield Loss Associated With Angular Leaf Spot Disease of Common Bean in the Southern Highlands of Tanzania.

Angular leaf spot (ALS) caused by Pseudocercospora griseola is among the devastating diseases of common bean (Phaseolus vulgaris L.) in the Southern Highlands of Tanzania (SHT). This study was conducted to assess the agronomic performance and economics of yield loss associated with the disease on five bean cultivars that are widely grown by farmers. The cultivars were evaluated in a split plot design with a randomized complete block arrangement during 2012/2013 and 2013/2014. The main plots were two rates of fungicide and a control whereas the subplots consisted of cultivars. Data were collected on disease severity, yield, and yield components. Analysis of variance was done and marginal rate of returns determined using partial budget. Results indicated significant decrease in yields, number of pods, seeds, and seed weight at P < 0.05 for untreated plots. Decreases in yield were associated with ALS disease severity that in turn was influenced by cultivar and rate of fungicide used. Higher grain yield losses of as much as 61% and the lowest marginal rate of returns were recorded for unsprayed plots during heavy rains. Fungicide usage at the recommended rates should be considered during heavy rains and breeding for resistance should be taken as an economical and sustainable strategy for managing the disease.