oat leaf blotch / Pyrenophora leaf spot

Symptoms

Brown elongated leaf lesions with yellow halos, lesions expand into large necrotic blotches, premature leaf death from base of plant upward, severe attacks cause grain shrinkage + reduced thousand-grain weight, seedling stunting from seedborne inoculum.

Plants affected

• oat

Easily confused with

• crown rust of oat

  How to tell them apart: Both diseases speckle oat (Avena sativa) leaf blades, but the texture decides it. Puccinia coronata (crown rust) forms small, raised, bright orange-yellow pustules (uredinia) that erupt through the blade and the leaf sheath; rub them with a fingertip and they smear off as rusty-orange powder, and late in the season they darken to brown-black telia. Pyrenophora avenae (oat leaf blotch) instead makes flat, dry, reddish- to chocolate-brown necrotic spots, blotches and short stripes — often ringed by a yellow halo — that stay sunken and inside the leaf surface and never rub off as powder. Rule of thumb: powdery orange dust on your finger = crown rust; flat brown dead patches that smudge nothing = Pyrenophora leaf blotch.

Common questions

How do I recognise oat leaf blotch / Pyrenophora leaf spot on oat?

Brown elongated leaf lesions with yellow halos, lesions expand into large necrotic blotches, premature leaf death from base of plant upward, severe attacks cause grain shrinkage + reduced thousand-grain weight, seedling stunting from seedborne inoculum.

Do I have to report oat leaf blotch / Pyrenophora leaf spot?

No. oat leaf blotch / Pyrenophora leaf spot is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is oat leaf blotch / Pyrenophora leaf spot treated?

Mainly with biological and cultural measures — removing affected material, changing the conditions that favour it, and treating with agents approved in your country. The exact steps and their timing depend on the plant, the season and where you live: Dr. Phyto works them out in a free diagnosis.