CropAlert – Disease risk update (August 2023)

CropAlert – Disease risk update (August 2023)

As the weather begins to dry out, the risk of disease resulting in significant yield loss in crops will reduce.

It remains important for growers to monitor their paddocks. There are still high levels of pathogens (disease causing agents) in paddocks and the resistance rating of the crop/variety will affect the disease risk in individual paddocks. However, the environmental conditions will determine the impact of disease and yield loss this season. Heavy dews and regular, light showers can be enough to drive disease infection.

Higher risk paddocks are those that have had early, high disease pressure and where crops have been sown in tight rotation (e.g. lentil-wheat-lentil-wheat, wheat-canola-wheat, or wheat-wheat).

To help growers assess the risk and help monitor for disease, we have listed the current status and potential risks of key crop diseases below. Please note that this is based on industry reports and growers may see other diseases in their paddocks.


Stripe rust – was reported 2 weeks earlier than usual and across the eastern seaboard. While this is not as early as the 2022 epidemic, it is still an increased risk compared with an average year. Crops will need to be monitored and actively managed where stripe rust symptoms are found to reduce the impact. For further information on the situation please download the July cereal rust report from the Australian Cereal Rust Survey.

Septoria tritici blotch – has emerged as a disease of concern in the medium and low rainfall zone. In the medium and high rainfall zones, susceptible varieties in close wheat rotations (1 in 2 years) will need a follow-up fungicide at Z39 to avoid yield loss. A follow up head wash may also be required if the spring becomes wet.

Crops in low rainfall regions are also experiencing higher levels of Septoria infections than in past seasons. If dry weather prevails, it is highly unlikely to cause yield losses. Where susceptible to very susceptible varieties are sown into high risk situations, control options should be considered.

Managing septoria may offer control of stripe rust too as most fungicides offer dual control of both the diseases.

Crown rot – watch for deadheads in wheat this year. If there is a dry finish, soil-borne diseases such as crown rot are likely to appear as deadheads in crop. Paddocks that have high levels of crown rot during 2023 will need to be managed for 2024. Fusarium head blight (FHB) infection found during 2022 was mainly caused by crown rot pathogens. Where the infected seed was sown, the risk from crown rot is likely to be high if the predicted El Nino becomes apparent. It is unlikely FHB will be an issue during 2023, unless we have another wet spring similar to 2022.


Net form of net blotch – please note that fungicide resistance to Group 7 (SDHI) was detected in South Australia during 2022. If this resistance has spread to Victoria, then seed dressings containing fluxapyroxad and other Group 7 fungicides will have lost their efficacy. If you have noticed field failure of any of these chemicals, please contact the Horsham Field Crops Pathology Team or send in samples for fungicide resistance testing.


Red leather leaf (RLL) – has been detected in oat crops in the Wimmera and Southern Mallee regions. Current conditions suit the disease development and spread. If dry weather returns, the disease is highly unlikely to cause yield losses.

Lentil and Vetch

Ascochyta blight – this has appeared in crops 6 weeks earlier than during 2022 and symptoms have been severe (stem breakages). Crops with these early symptoms will need monitoring even if a dry spring eventuates as the conditions required for crop disease to continue to develop can occur even when rainfall is low. If rain occurs during podding, the pods will need to be protected.

Botrytis grey mould (BGM) – similarly to Ascochyta blight, BGM was detected early in crops this year. Early fungicides will have controlled some of the disease, but crops will need canopy closure sprays and monitoring.

Faba bean

Cercospora – was detected early in faba bean crops. Where this early infection was not well controlled, crops should be monitored for other diseases such as chocolate spot. Crops infected with Cercospora will be more susceptible to chocolate spot.

Chocolate spot/Botrytis – monitor for symptoms. Waterlogged areas will be more prone and crops that have been affected by Cercospora will also be more susceptible.

Field pea

Bacterial blight – several frosts this season have increased the risk of bacterial blight in field pea crops. Monitor for symptoms and if a paddock or section of paddock is affected, avoid spreading the disease to other paddocks through good hygiene. Retain seed from clean paddocks. Fungicides do not control Bacterial blight.


Further information

Further information on these and other field crop disease can be found in the online Identification & Management of Field Crop Diseases in Victoria manual.


Horsham Field Crop Diseases research group (Agriculture Victoria)

For further information and assistance in diagnosing field crop diseases, contact the Horsham Field Crop Diseases research group.

Ph: (03) 5450 8301

Email: [email protected]

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