Leafspot of Taro ( Colocasia Esculenta (L.)Schott) in Ghana and suppression of symptom development with thiophanate methyl

A foliar disease of taro ( Colocasia esculenta (L.) Schott) in Ghana, which manifests as diffuse, circular to irregular spots, mostly on older leaves ultimately resulting in leaf blight, was found to be caused by Cladosporium colocasiae (Saw.). Isolates of C. colocasiae used in pathogenicity tests were virulent on taro but generally non-pathogenic to cocoyam ( Xanthosoma sagittifolium (L.) Schott). A study of disease progress on individual leaves of upland taro indicated that spots appear on newly unfurled leaves after 12 days and the leaf blight stage occurs 24 days later. Of sixty-four taro plantings surveyed in nineteen towns and villages, forty-six (71.9%) were growing in swamps, twelve (18.8%) under semi-upland conditions and six (9.3%) under strictly upland conditions. The disease was observed in fifty-eight (90.6%) of the plantings. It was either absent or unimportant on swamp-grown taro, moderate on semi-upland taro and most severe on the upland crop. In an upland field trial, each of the six different application rates and spray schedules tested with Topsin M (thiophanate methyl 70 WP), significantly reduced disease progress. Thus, leaf spotting disease could be effectively managed with the fungicide in the upland/semi-upland regions of Ghana.