Diagnosing wirrega blotch

A fungal foliar disease caused by Pyrenophora wirreganensis that primarily infects a range of grasses and can be found on paddock and road verges in spring. Leaf infections are rarely severe as spores produced on the leaves do not re-infect leaves and so do not increase the disease in crops.

Large elongated mid-brown blotches surrounded by a margin of chlorotic tissue
Tissue at the centre of the blotch dies and in some cases a hole forms.
The blotches expand eventually covering the entire leaf.

What to look for

    Plant

  • Large elongated mid-brown blotches surrounded by a margin of pale tissue that frequently extends towards the leaf tip.
  • Tissue at the centre of the blotch dies and in some cases a hole forms.
  • The blotches expand and may eventually cover the entire leaf.

Where did it come from?

Grass weeds
Grass weeds
Contaminated seed
Contaminated seed
  • Spores from previously infected grass seed in the soil blow or are splashed on to leaves.
  • Spores from these leaf infections do not affect other leaves, but infect florets.
  • Seeds from infected grass florets do not germinate but fall to the ground to provide inoculum for the following year.
  • Infections are worse where grass weeds were a problem in previous years.

Management strategies

Grass weed control
Grass weed control
Grass pasture control
Grass pasture control
  • Reduce grass weed burdens in previous crop or pasture phases.
  • Reduce grasses, including barley and brome grass.
Source URL: https://www.agric.wa.gov.au/mycrop/diagnosing-wirrega-blotch
This print version was generated at 6:46pm on the 9th of May, 2025.
The original document was last revised at Fri, 17/04/2015 - 2:26pm

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The Chief Executive Officer of the Department of Primary Industries and Regional Development and the State of Western Australia accept no liability whatsoever by reason of negligence or otherwise arising from the use or release of this information or any part of it.