The development of eyespot (Pseudocercosporella herpotrichoides) lesions in winter wheat crops

Abstract

The development of eyespot (Pseudocercosporella herpotrichoides) lesions on main shoots of plants in winter-sown wheat crops in 1981/82, 1982/83 and 1983/84 was studied by recording the incidence and penetration of leaf sheath infections from January to April/May and the incidence and severity of stem lesions from April/May until harvest in July/August. The incidence of leaf sheath infection in a late-sown (3 Nov 1982) crop increased from 15 per cent in January to 60 per cent in March 1983, but decreased during April and May. The mean number of leaf sheaths penetrated per mains shoot increased from 1 in January to 3.5 in May. The crop was sown earlier (9 Sept) in 1983 and after a wet, mild autumn 80 per cent of the plants were infected, with three leaf sheaths penetrated on the main shoots, by January 1984. The incidence of infection changed little in the following 3 months and four leaf sheaths had been penetrated by late April. In 1982, eyespot lesions had become established in main stems of 70-80 per cent of the plants in the crop before the last leaf sheaths at the stem base had withered in mid-June. These lesions became more severe during June and July. In 1983 and 1984, only 20-40 per cent of plants had visible lesions on their mains stems when leaf sheaths had withered and, although the incidence of visible stem lesions increased subsequently, the lesions never became severe