Nodorum blotch in wheat
Wheat seedlings from Esperance recently submitted to DPIRD’s Diagnostic Laboratory Services (DDLS) have been diagnosed with nodorum blotch (previously known as septoria nodorum blotch). The disease is caused by the fungus Parastagonospora nodorum. The plants were volunteer regrowth emerging through 2021 stubble following autumn rainfall.
Nodorum blotch is a stubble-borne disease, favoured by warm, wet weather, and severe damage can occur after heavy and frequent rain particularly in wheat-on-wheat situations. Infected regrowth poses a negligible risk to other crops in the region but does demonstrate that proximity to infected stubble is a key risk in the disease cycle.
Plant leaves infected with nodorum blotch have tan-brown oval or irregular shaped leaf blotches with yellow margins. Tiny brown fruiting bodies can occasionally be seen in lesions but are not easily visible to the naked eye. Badly affected leaves die back from the tip as blotches converge.
Lower leaves are affected on young plants.
Later in the season, nodorum blotch can spread to glumes (known as glume blotch) and stems, and heavy infection may cause blotching across the entire grain head with shrivelled grain at harvest causing yield and grain quality losses.
In WA, nodorum blotch often occurs in a disease complex with yellow spot on wheat. Yellow spot lesions more often start as yellow rather than tan, and fruiting bodies are not present in leaf lesions. It is very difficult though to distinguish yellow spot from nodorum blotch by visual leaf symptoms even for experienced plant pathologists who rely on lab diagnostic techniques to confirm which pathogen is present. Heads and glumes are not affected with yellow spot.
Leaf samples can be submitted to DDLS Plant pathology services for diagnosis of which pathogen is causing the symptoms. This can be worthwhile, particularly as symptoms may not actually be fungal. Leaf spot symptoms can sometimes be physiological, and these do not respond to fungicide application.
For more information refer to DPIRD’s Diagnosing septoria nodorum of wheat page.
Varieties differ in susceptibility to nodorum blotch.
Greatest yield response to fungicide application for nodorum blotch in wheat canopy is achieved through application at flag leaf emergence. However, earlier application (eg at first node, Z31) may be considered if a susceptible variety has been sown into wheat stubble or disease pressure is high early, particularly if there is yellow spot present. When the disease is seen moving up the leaf canopy after flag leaf emergence, infection of heads (glume blotch) is a risk and this can cause significant loss of yield and grain quality. Glume blotch is best prevented by application of a registered fungicide when the crop is at grain ear emergence (Z55 - 59).
Growers should prioritise disease management of wheat sown on wheat stubble, especially early sown susceptible wheat crops, as these are likely to be more vulnerable to developing disease, especially glume blotch, because they have heads exposed for longer.
YellowSpotWM is a free app available to assist with making economic fungicide spray decisions for managing yellow spot in wheat. Users can specify factors relating to paddock selection, variety, seasonal conditions, prices and management options so that the output relates to their cropping circumstance. For more information refer to DPIRD’s YellowSpotWM page.
More information on registered fungicides can be found at DPIRD’s Registered foliar fungicides for cereals in Western Australia page.
Further information about this disease can be found at the department’s Managing yellow spot and nodorum blotch in wheat page.
For more information on wheat diseases contact Plant Pathologists Andrea Hills, Esperance on +61 (0)8 9083 1144, Ciara Beard, Geraldton on +61 (0)8 9956 8504, Geoff Thomas, South Perth on +61 (0)8 9368 3262, or Kithsiri Jayasena, Albany on +61 (0)8 9892 8477 .
Article author: Ciara Beard (DPIRD Geraldton).
Article input: Geoff Thomas (DPIRD South Perth), Hossein Golzar (DPIRD South Perth), Jean Galloway (DPIRD Northam) and Manisha Shankar (DPIRD South Perth).