Mainly wheat, but also occasionally on rye, triticale and some grass species.
Symptoms of Septoria can be seen very early in the growing season in most years. On young autumn-sown wheat, water-soaked patches which quickly turn brown and necrotic may be evident by early December and throughout the winter on the lowest leaves. These contain the visible black pycnidia which are the most characteristic feature of M. graminicola. Pycnidia are particularly common on dead overwintering leaves of winter wheat. Lesions on the mature plant are brown and are sometimes restricted by veins giving rectangular appearance. The black pycnidia become visible in the lesions as the symptoms develop. Lesions may coalesce leading to large areas of necrotic brown tissue.
The disease cycle of M. graminicola is similar to that of S.nodorum, although M. graminicola can go through its life cycle at slightly lower temperatures (15-20°C optimum), and requires longer periods of high humidity to initiate infection. The lower leaves of winter sown crops are normally infected by long distance spread of air-borne ascospores throughout the winter and early spring. In the spring the lower leaves of the most susceptible varieties are infected and have actively sporulating lesions. Most disease spread to upper leaves occurs by rain-splash from the lower leaves which occurs during heavy rainfall. Physical spread can occur without heavy rainfall, particularly when leaves 3 and 4 overlap the upper leaves as they emerge.
The disease is the most important foliar disease on winter wheat in the UK. Losses of 50% have been reported in severely affected crops. This is largely because of the predominance of varieties which are susceptible to the disease.
There are no practical cultural control measures for S.tritici although date of drilling has a marked effect on disease establishment. Early drilled crops are exposed to incoming ascospores for longer periods and hence tend to have higher levels disease through the winter and early spring period. Later drilled crops may carry lower levels of disease through the winter period but this has little effect on the final level of disease in the crop as inoculum is rarely limiting, the final level of disease being determined largely by weather conditions during stem extension.