Symptoms of halo spot disease of barley

Halo spot symptoms are most often observed on infected barley crops in wet seasons. Find out how to identify the classic lesions and tell them apart from other foliar diseases.

Typically, this sporadic barley disease occurs where rainfall is high (e.g. south-west of England).

Generally, it does not cause significant yield loss.

The pathogen (Selenophoma donacis) originates from infected seed, stubble and volunteer barley plants.

Barley can be infected in the spring and autumn.

The disease appears as small leaf spots (1–3 mm long), often square or rectangular in shape, pale brown in the centre, with dark purple/brown, well-defined margins.

Generally, spots occur towards the tips and along the edges of leaves (especially the upper leaves). They also affect the leaf sheath and ear (especially the awns).

Dark-coloured pycnidia occur in lines along the veins within the central area of a lesion.

This disease often occurs with rhynchosporium, but can be distinguished from it by the presence of pycnidia. The spots also tend to be smaller. Rhynchosporium is also more common on older foliage.

Symptoms on lower leaves, which arise from seed infection or from stubble contact or splash, are indistinct, but rain splash helps to spread them up the plant – usually in warm conditions later in the season.

The disease rarely becomes important until after flag leaf emergence, when it can develop rapidly in wet weather.