Yield losses caused by Colletotrichum gloeosporioides in three species of Stylosanthes

Abstract

Yield losses from the fungal disease anthracnose, caused by Colletotrichum gloeospovioides, were estimated for 3 species of Stylosanthes grown in northern Queensland. Naturally infected control plots of S. scabra cv. Fitzroy, S. hamata cv. Verano and S. guianensis cv. Graham were compared with plots protected by 3 benomyl spray treatments designed to restrict anthracnose development to 0, 25 and 50% of the level sustained in the unsprayed control plots. Following initial infection in early February 1984, disease incidence and severity in Fitzroy and Verano reached a maximum during early March. This rapid build up of disease was associated with a period of sustained wet weather. Graham only became infected much later in the season as the plants matured, and sustained severe anthracnose lesions on both leaves and stems even though weather conditions appeared unsuitable for an epidemic. Yield losses were severe in all 3 cultivars. Average dry matter yields of the unsprayed controls were only 21.6, 66.7, and 53.5% respectively of the yields of the disease free plots for Fitzroy, Verano and Graham. Corresponding seed yields were 15.6, 48.9 and 42.5% respectively. Highly significant negative correlations were found between dry matter and seed yields of the 3 species and the incidence and severity of anthracnose disease.