Leaf rust in wheat
- Grass Patch
Quenten Knight (Agronomy Focus) has reported finding leaf rust on a Catapault wheat crop near Grass Patch. There were low isolated pustules of rust in the lower canopy, mainly on senescing leaves. The plants were at stem elongation.
Leaf rust pustules are small, circular to oval and can vary in colour from orange to light brown. They usually appear on the upper surface of leaves and on leaf sheaths in cases of heavy infection. Leaf rust requires moisture (rain or heavy dew) or high humidity for spores to germinate and infect leaves. Usually, 4-6 hours of leaf wetness are required at optimum temperatures 15-25°C (warm days and dewy nights) for disease to spread rapidly. The primary risks for carryover of rusts are wheat regrowth and volunteer wheat at edges of paddocks or roadsides. This means that it is worth inspecting as well as planting these crops.
When checking wheat, growers and consultants are also urged to investigate the bottom of the canopy and stems for the presence of stem rust. Stem rust is favoured by warm spring conditions (20-35°C). Stem rust pustules are a darker red-orange and are often found with ragged edges. For more information refer to the Department of Primary Industries and Regional Development (DPIRD)’s managing stem rust of wheat page.
Management
Variety selection is the best defence against rust diseases in-crop. Varieties rated as moderately resistant to moderately susceptible (MRMS) or better will show significantly less rusting than a susceptible (S) variety. These varieties are unlikely to require a fungicide application to maintain grain yield except in exceptional years with very high disease pressure. For variety disease ratings, refer to DPIRD’s 2023 WA Crop Sowing Guide – Wheat.
If rust is detected in a susceptible variety (rated VS to S), fungicide is more likely to be needed to protect yield. In these cases, fungicide should be applied before the epidemic becomes severe, taking into consideration the stage of crop development. Spraying after crop flowering is normally not economic for leaf rust. As the season progresses and warmer, drier conditions occur, the likelihood of an economic response to fungicide will diminish. Spraying decisions should consider the level of disease in the crop, varietal susceptibility, the time of the season and growth stage of the crop. Additionally, consider the chance of ongoing rainfall after spraying, as this is favourable for disease development. Use high rates of fungicide for longer duration of protection, for example, when season conditions favouring infection are likely to persist, or for more susceptible varieties. Cost should be tuned to crop yield potential and crop season length. For a list of registered fungicides to use as foliar sprays, visit DPIRD’s registered foliar fungicides for cereals in Western Australia page.
Rusts predominantly spread via wind from infected plants, but spores can also be transported through the movement of people, machinery and plants. Growers are urged to adopt hygiene (biosecurity) measures during their paddock checks to reduce the risk of spreading the disease. If you are monitoring, the best place to look for rusts is in green plants in tramlines.
Rust pathotype testing
Growers and agronomists are encouraged to send samples of all rusts for pathotype testing at any time of the year to the Australian Rust Survey. Possible new rust strains need to be continuously monitored for as they have implications for existing varieties, and this will assist wheat breeders in developing new resistant varieties. Infected leaf samples should be mailed in paper envelopes (do not use plastic wrapping or plastic lined packages) along with your details and collection information (location, variety etc.) directly to The University of Sydney, Australian Rust Survey, Reply Paid 88076, Narellan NSW 2567. Optional free reply-paid envelopes can be ordered from University of Sydney. For further details refer to the University of Sydney’s Australian Cereal Rust Survey page.
More information
For more information on wheat leaf rust, refer to DPIRD’s managing stripe rust and leaf rust in Western Australia and diagnosing leaf rust of wheat pages.
For more information on leaf rusts, contact Plant pathologists Ciara Beard in Geraldton on +61 (0)8 9956 8504, Kithsiri Jayasena in Albany on +61 (0)8 9892 8477, Geoff Thomas in South Perth on +61 (0)8 9368 3262, Kylie Chambers in Northam on +61 (0)8 9690 2151 or Andrea Hills in Esperance on +61 (0)8 9083 1144.
Article authors: Ciara Beard (DPIRD Geraldton), Andrea Hills (DPIRD Esperance), Geoff Thomas (DPIRD South Perth) and Cindy Webster (DPIRD Narrogin).
Nodorum blotch and yellow spot in wheat
- Geraldton
- Dalyup
- Coomalbidgup
Plant pathologist Ciara Beard (DPIRD) recently found nodorum blotch and yellow spot in flowering regrowth wheat on a roadside near Geraldton and symptoms are becoming evident in sown crops.
Agworld users have reported finding yellow spot in wheat near Geraldton, and nodorum blotch near Dalyup and Coomalbidgup
The disease nodorum blotch (previously known as septoria nodorum blotch) is caused by the fungus Parastagonospora nodorum. Yellow spot is caused by the fungus Pyrenophora tritici-repentis.
In WA, nodorum blotch and yellow spot often occur together as a disease complex on wheat, and are difficult to visually distinguish.
These pathogens are stubble-borne and are therefore high risk in wheat-on-wheat situations. Crop infection is favoured by warm, wet weather. Nodorum blotch is promoted by heavy and frequent rain, while dew can be enough to spread yellow spot. Infected regrowth poses a negligible risk to crops in the region, and demonstrates that proximity to infected stubble is a key risk in the disease cycle.
Symptoms
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.
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. Shrivelled grain at harvest causes yield and grain quality losses. For information, refer to DPIRD’s diagnosing septoria nodorum of wheat page.
Yellow spot lesions often start as yellow-tan oval spots on leaves that become tan-brown in their centre with a yellow edge as lesions grow. Fruiting bodies are not present in leaf lesions. It is very difficult 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 rarely affected with yellow spot. For more information, refer to DPIRD’s diagnosing yellow spot of wheat page.
For diagnosis of which pathogen is causing the symptoms, leaf samples can be submitted to DPIRD’s Diagnostic and Laboratory Services (DDLS) Plant pathology services. Correct diagnosis 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. Samples can be delivered in-person or addressed to:
DPIRD Diagnostics and Laboratory Services
DDLS Specimen Reception Interim Lab Building 102
Department of Primary Industries and Regional Development
3 Baron-Hay Court
South Perth WA 6151
For more information, email or phone DDLS on +61 (0)8 9368 3721.
Management
Varieties differ in susceptibility to nodorum blotch and yellow spot.
Greatest yield response to fungicide application for nodorum blotch or yellow spot in wheat canopy is achieved through application at flag leaf emergence. However, earlier application (e.g., at first node, Z31) may be considered if a susceptible variety has been sown into wheat stubble. Earlier application may also be considered if disease pressure is high early, particularly when there is yellow spot present. When nodorum 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 in Esperance on +61 (0)8 9083 1144, Ciara Beard in Geraldton on +61 (0)8 9956 8504, Geoff Thomas in South Perth on +61 (0)8 9368 3262, or Kithsiri Jayasena in Albany on +61 (0)8 9892 8477.
Article author: Ciara Beard (DPIRD Geraldton).
Article input: Geoff Thomas (DPIRD South Perth), Kithsiri Jayasena (DPIRD Albany), Jean Galloway (DPIRD Northam) and Manisha Shankar (DPIRD South Perth).
Loose smut in barley
- Central grainbelt (Northam)
- Eastern grainbelt (Merredin and Yilgarn)
Plant pathologist Dr Kylie Chambers (DPIRD) has recently been finding loose smut in barley crops in the central (Northam) and eastern grainbelt (Merredin and Yilgarn).
Barley loose smut is a fungal disease affecting seed heads, which can cause yield losses.
In plants grown from infected seed, florets are replaced with a compact mass of dark brown-black powdery spores at heading. These spores are dispersed by wind to infect adjacent plants and produce the next generation of infected seed. Infection is favoured by rainfall and high humidity during flowering.
When examining your paddock, look for scattered plants with black heads or bare flower stalks. Infected seed is symptomless, and presence of infected plants in the source paddock is a good indicator of risk of harvesting infected seed.
Management
Infected seed is the primary disease source, and highly contaminated seed should not be re-sown.
Transmission of infection from seed can be easily and effectively managed with a registered fungicide seed dressing.
Research conducted by Dr Kithsiri Jayasena (DPIRD) has found high label rates of a tebuconazole-based product, applied during flowering, can also reduce seed borne loose smut embryo infection on susceptible barley.
For more information on barley loose smut, refer to the Department's webpages:
- Diagnosing barley loose smut.
- Controlling barley loose smut.
- Smut and bunt diseases of cereal - biology, identification and management.
For more information, contact Plant pathologists Kithsiri Jayasena in Albany on +61 (0)8 9892 8477, Geoff Thomas in South Perth on +61 (0)8 9368 3262, Andrea Hills in Esperance on +61 (0)8 9083 1144, Ciara Beard in Geraldton on +61 (0)8 9956 8504 or Kylie Chambers in Northam on +61 (0)8 9690 2151.
Article authors: Cindy Webster (DPIRD Narrogin), Kithsiri Jayasena (DPIRD Albany), Andrea Hills (DPIRD Esperance) and Ciara Beard (DPIRD Geraldton).
Article input: Kylie Chambers (DPIRD Northam) and Geoff Thomas (DPIRD South Perth).