Yellow spot in wheat
Belinda Eastough (Elders) reports finding yellow spot at high levels in a Calingiri wheat crop at Nabawa. The noodle crop was sown on wheat stubble (Scepter in 2017) and is at early tillering stage. The grower will be applying foliar fungicide shortly when spraying out weeds. The crop received flutriafol in-furrow at seeding but this is not registered for yellow spot.
An Agworld user has also reported yellow spot in a wheat crop near Binnu.
Yellow spot can be a problem for crops where early season rains provide suitable conditions for the disease development. The disease survives over summer on infected stubble and with the onset of wet conditions releases spores which infect new seedlings especially when there are frequent periods of wet/moist leaf surfaces.
Yellow spot and septoria diseases have similar looking symptoms and frequently occur together throughout the wheatbelt. Septoria tritici blotch is considered rare in WA. These diseases are particularly a problem in continuous wheat crops in stubble retention farming systems as they are stubble-borne.
They appear in wheat as irregular or oval-shaped spots that initially are small and yellow, but enlarge to form brown dead centres, with yellow edges. Typically, a badly affected leaf will die back from the tip as lesions merge, reducing the photosynthetic area and causing premature leaf death.
These diseases have the capacity to significantly reduce yield (by up to 30%) and grain quality in medium-high rainfall areas or other areas receiving above average rainfall this growing season.
Spores produced on infected lower canopy leaves provide inoculum for later season disease development, early application of a registered foliar fungicide can reduce sporulation on these leaves.
For wheat after wheat, when there is high disease pressure prior to stem elongation, it may be economic to apply a registered fungicide at or prior to early stem elongation (Z31, first node) particularly in medium to high rainfall areas. A second spray may be required at or after flag leaf emergence if disease is moving up the canopy and the outlook is for good finishing rains.
A list of registered fungicides to use as foliar sprays are available at Registered foliar fungicides for cereals in Western Australia.
For further information on yellow spot refer to;
- DPIRD’s Diagnosing yellow spot in wheat page
- DPIRD’s Managing yellow spot and septoria nodorum blotch in wheat page
- CCDM’s The Spotlight May 2017 X-Men or Batman – which one is yellow spot? newsletter article.
For more information contact Ciara Beard, Plant Pathologist, Geraldton on +61 (0)8 9956 8504, Geoff Thomas, Plant Pathologist, South Perth on +61 (0)8 9368 3262, Andrea Hills, Plant Pathologist, Esperance on +61 (0)8 9083 1144 or Kithsiri Jayasena, Plant Pathologist, Albany on +61 (0)8 9892 8477.