Net Blotch

Pathogen

Pyrenophora teres f. teres (Drechslera teres) Pyrenophora teres f. maculata (spot form)

Hosts

The disease affects a wide range of grasses but the forms on barley are specific to that crop and do not affect other cereals or grasses.

Symptoms

Infection of young seedlings with net blotch can look very similar to leaf stripe infection - the first leaf often has a single brown stripe extending the whole length of the leaf. However, later leaves do not usually show striped symptoms. Leaves infected by splash-borne spores typically show short brown stripes or blotches with a network of darker lines at random on the leaves. The disease tends to produce 'stripe' symptoms or 'netting' symptoms which are distinctly different in appearance. There is also another, less common symptom which is termed 'spot blotch' where lesions are more oval in appearance. Leaves frequently have yellowing associated with all of these types of lesion, particularly when the symptoms are severe. The glumes and awns can also be affected, producing dark brown flecking and striping.

Life Cycle

Net_Blotch-life-cycle.jpg

Seed-borne mycelium infects the coleoptile and the first leaf becomes infected as it emerges. Spores produced on this first leaf serve to spread the disease to other leaves and to surrounding plants. Seedborne inoculum is usually much less important than infected stubble and debris which allows the pathogen to over-winter. Trash and crop debris provides much higher levels of inoculum which is splash borne up the plant. Although there are suggestions of long distance spread of ascospores from overwintering pseudothecia the role of these is not thought to be as important as trash-borne inoculum.

Importance

Because the seed-borne phase is relatively unimportant compared with trash-borne inoculum the seedborne phase does not often threaten yield. Net blotch is now a very important disease of barley and can cause large losses where the disease is not well controlled. The disease can be particularly damaging when symptoms continue to develop through the winter and into the early spring, producing an early epidemic as the crop develops.

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