Ascochyta Leaf Scorch (Spot) [Didymella exitialis]

Pest Profile

About the pest

Hosts

The disease affects wheat, barley, oats, rye triticale and many grass species.

Symptoms & Diagnosis

Symptoms

Disease symptoms are found on lower leaves early in the season and on upper leaves later on. The lesions are usually elliptical and although chlorotic at first, soon become buff to brown in colour, often splitting longitudinally. Initially lesions have a dark brown margin with a papery white centre. The fungus often invades damaged leaf tissue such as that caused by liquid urea or nitrogen. Symptoms become less distinct with time and become very similar to those caused by S. nodorum. Pycnidia within the lesions are generally black, distinguishing the disease from S. nodorum which tends to have light coloured pycnidia.

Life cycle

Pycnidia and mycelium within leaf tissue are thought to survive on crop debris, much like the Septoria pathogens.

Remarks

Importance

The disease is of relatively minor importance although in individual crops it is likely to add to leaf death in the same way as the Septoria diseases. Symptoms are often seen later in the season towards the end of grain filling when they are unlikely to cause any yield loss. The teleomorph stage of the fungus (Didymella exitialis) is common in Europe and the air-borne ascospores of the fungus are commonly found in late summer in the UK, where they have been implicated in late summer asthma.