Leaf Blotch [Zymoseptoria tritici]

Pest profile

Symptoms & Diagnosis

Occurence

Mainly wheat, but also occasionally on rye, triticale and some grass species.

Pattern of damage

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 over-wintering leaves of winter wheat. Lesions on the mature plant are brown and are sometimes restricted by veins giving a rectangular appearance. The black pycnidia become more visible in the lesions as the symptoms develop. Lesions may coalesce leading to large areas of necrotic brown tissue.

Life cycle

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 with 15-20°C as the 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 airborne 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 during heavy rainfall. Physical spread can occur without heavy rainfall, particularly when leaves 3 and 4 overlap the upper leaves as they emerge.

Remarks

This 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.