Yellow spot of wheat

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Yellow Spot is a stubble-borne fungal leaf disease of wheat caused by Pyrenophora tritici-repentis. It occurs commonly throughout the Western Australian wheatbelt and can reduce grain quality and cause yield losses of up to 30%.

What to look for

Paddock

  • Yellowing leaves, dying back from tips and scattered through a paddock.

Plant

  • Lower leaves affected in young crops.
  • Yellow-tan oval spots or lesions on leaves that become tan-brown in their centre with a yellow edge as lesions grow.
  • Lesions near leaf tips cause leaf yellowing and withering.
  • Look for small black fruiting bodies on stubble which have short, black hair-like projections and feel rough to touch.

What else could it be?

Condition Similarities Differences
Septoria nodorum blotch Tan blotches with yellow margins Oval to irregular blotches. Tiny brown fruiting bodies in blotches, however these may not be evident to the naked eye. Frequently attacks heads and glumes.
Septoria tritici blotch Tan blotches often without yellow margins Blotches irregular, often interveinal, not oval. Tiny black fruiting bodies in blotches, typically visible to the naked eye.

Septoria nodorum blotch and yellow spot often occur together and are generally impossible to distinguish by the naked eye.  Septoria tritici blotch is considered rare in Western Australia (WA).

Where does it come from?

  • Yellow spot survives on wheat stubbles.
  • After rain, fungal spores are ejected from sexual fruiting bodies on stubble onto nearby seedlings.  Secondary generation of asexual spores occurs on blotched leaves which are then widely dispersed on wind, infecting new leaves or other wheat paddocks.
  • Continuous wheat crops and retaining stubble significantly increase the risk of this disease. Early sown susceptible varieties and extended wet conditions can result in an increased disease severity.

Management Strategies

Generally an application of foliar fungicide to manage yellow spot or septoria diseases is more likely to be economic when:

  1. It has good yield potential
  2. There is a good chance of 100 millimetres (mm) or more rainfall after crop flag leaf emergence.
  3. When applied at or around flag emergence (Z39) to protect the flag and flag-1 leaves, which contribute the most to filling grain.

Other treatment options:

  • Crop rotation with any non-host crop (e.g. barley, canola, lupins, oats, pulses).
  • Reduce surface wheat stubble before seeding wheat after wheat.
  • Sow varieties with higher levels of resistance.
  • If disease is severe early, consider a foliar fungicide spray around first node (Z31), a second spray may be required around flag leaf emergence.

Contact information

Ciara Beard
+61 (0)8 9956 8504
Geoff.j Thomas
+61 (0)8 9368 3262
Kithsiri Jayasena
+61 (0)8 9892 8477
Andrea Hills
+61 (0)8 9083 1144
Page last updated: Friday, 26 August 2016 - 1:46pm