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Causal organism - Septoria tritici (Mycosphaerella graminicola)
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The disease cycle of S.tritici is similar to that of S.nodorum, although S.tritici can go through it's 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 rainsplash 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.
Importance
The disease is arguably 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.
