Plant Pathology: Extension: Plant Disease Library

Helminthosporium

Important diseases:  Southern corn leaf blight, Net blotch of barley, Victoria blight of oats, Helminthosporium blight (Melting out) of turf grasses, Black pox on apple & pear, and Blister canker of pear.

Helminthosporium causes leaf spots and blights on grasses, cereal crops and corn. This fungus is easily isolated from dead turf (thatch) and other weakened and dead plant tissue as a saprophyte. Different species of Helminthosporium are now actually known as three different fungi, Dreschlera, Bipolaris, or Exserohilum, but for the sake of brevity we will refer to all of these as Helminthosporium.

The fungus causes a variety of symptoms depending on the disease and host. On corn (Southern corn leaf blight) Helminthosporium causes small, tan, elliptical leaf spots. Net blotch of barley symptoms are small, brown almost square shaped, net-like blotches that spread along the leaf blade. Yellow stripes along the older leaf blades and sheaths are symptoms of Stripe disease of barley. Victoria blight of oats, which occurs exclusively on that variety, causes necrotic lesions on seedlings which kills the plant or develop into reddish to black stripes on the young leaves. Helminthosporium on turf and pasture grasses causes leaf spots, blights, and crown rots. The leaf spots have a reddish border and a grey center as they enlarge. Leaf spots may cause death of the leaf blade and crown. In addition, Helminthosporium causes small, black sunken spots on apple and pear fruit (black pox) as well as blister canker on pear.

 
Conidiophores of the fungus are simple or clustered, tall, erect, darkly pigmented and produce conidia at the apex.

Conidia are darkly to lightly pigmented, multi-celled cylindrical to extended ovals. Center cells tend to be wider than cells at the ends.