Strategies for disease management in 2025
Growers need to consider potential disease carryover into the 2025 growing season if wet conditions are experienced during summer and autumn resulting in weed and crop regrowth. This regrowth can serve as a ‘green bridge’ for diseases (biotrophs) and pests which need a living plant to survive, such as cereal rusts and powdery mildew, nematodes, root diseases and aphids. If weeds and/or volunteers are present at the start of the new cropping season, particularly in or adjacent to cropping paddocks, there is a greater risk of early spread of pests, viruses and diseases to newly emerging crops. Early pest, virus and disease outbreaks often have the greatest impact on grain yield potential.
This year, blackleg, sclerotinia stem rot and turnip yellows virus were prevalent in canola crops across the grainbelt. Lupins were affected by sclerotinia and bean yellow mosaic (necrotic) virus, particularly in northern areas that experienced above average winter rainfall. Barley was affected by loose smut and both forms of net blotch, while common wheat diseases observed included powdery mildew, septoria nodorum blotch and yellow spot mixed infections. The presence of leaf rust in wheat and oats, along with stem rust in oats, though observed at low levels and in some locations late in the season, is a warning for 2025.
Disease management strategies for 2025
To minimise the risk of carry over on the green bridge, growers are encouraged to monitor the following:
- Check the PestFacts WA map for disease reports by region in 2024. This includes above-ground foliar diseases and below-ground soilborne diseases and nematode pests. Identify the cause of any disease symptoms and/or poor patches observed in crops this season in order to put the right management plan in place for 2025. For further information on identifying and managing root diseases and nematodes see the 2024 PestFacts WA issue 17 article Diagnose patchy crops to form strategies for next season.
- Monitor any green bridge that is present in summer and autumn for disease and virus vectors (such as aphids), so that timely action can be taken to identify the pathogen and limit the spread and build-up of inoculum. It is crucial that growers eradicate weeds and crop volunteers, including those along fence lines, prior to the start of the cropping program. This will reduce potential pest and disease outbreaks, including foliar diseases, root diseases and viruses.
Ideally, there needs to be a break (a fallow period) of at least 2 weeks, free of vegetation capable of hosting disease and pests, prior to sowing. To achieve this, weeds and volunteers should be sprayed with a herbicide at least 4 to 6 weeks before sowing to ensure weeds are completely dead at planting.
Alternatives to herbicides include heavily grazing or cultivating weeds and crop volunteers, which will reduce their potential as a ‘green bridge’ or host of diseases and pests. However, growers should be aware that cultivating in high crown rot risk paddocks could be detrimental, as it may spread infected material, grass weeds and volunteers further. Fusarium crown rot was reported from several areas of the Esperance and Albany port zones this year. For more information refer to the 2024 PestFacts WA Issue 21 article Fusarium crown rot.
When managing the green bridge, growers need to consider retaining at least 50% ground cover to reduce the risk of erosion during crop establishment. Especially on soils that are prone to erosion.
In addition to managing the green bridge, other strategies growers can employ include the following:
- Sow cleaned and graded seed. Cleaning and grading seed will remove disease agents such as sclerotia or ryegrass ergot, preventing their spread and significantly improving the efficacy of seed dressing applications by reducing dust levels. DPIRD also provide a range of seed testing services, including fungal, bacterial and virus infection, through the DPIRD Diagnostic Laboratory Services – Plant pathology services.
- Know the latest disease ratings of your varieties and plan accordingly. Use adult plant resistant varieties. The DPIRD 2025 WA Crop Sowing Guide will soon be available on the DPIRD website, which details the disease susceptibility for each variety.
- Consider applying in-furrow or seed dressing fungicides to reduce your risk of early infection of diseases such as cereal rusts, net blotches and powdery mildew in susceptible varieties, and rhizoctonia, crown rot and take-all as well as blackleg crown canker in canola. Fungicide seed dressings are an important tool to employ in protection against cereal smut and bunt diseases. For more information see DPIRD’s Seed dressing and in-furrow fungicides for cereals in Western Australia and Seed dressing and in-furrow fungicides for canola in Western Australia.
- Insecticide seed treatments can be effective at preventing early aphid infestations and subsequent virus spread in some crops such as cereals. Seed treatments are less effective for controlling green peach aphid and turnip yellows virus in canola and should not be used solely to control them.
- Reduce exposure to stubble-borne diseases through rotation and careful paddock planning (to avoid sowing on or downwind of infected stubble) or stubble management practices, such as grazing, windrowing, baling, incorporation or burning. Wheat powdery mildew can be both stubble-borne and spread on green bridge.
- Avoid early sowing of susceptible varieties. Earlier sown crops are generally more at risk of foliar diseases such as powdery mildew, net blotches of barley, nodorum blotch and yellow spot of wheat so consider later sowing of susceptible varieties and at-risk paddocks. At the least, plan to monitor earliest sown paddocks closely for disease.
For more information refer to the DPIRD Control of green bridge for pest and disease management page and the Grains Research and Development Corporation's (GRDC) Green Bridge fact sheet.
Wheat flag smut and barley loose smut
Flag smut in wheat was at higher incidence in some regions this year and is of particular concern as it is both seed (externally on the seed coat) and soil borne. Where crops were infected this year, some harvested seed will be infected and soil in these paddocks should be considered to contain spores which could infect wheat crops for at least the next 2 to 3 years, possibly longer.
Barley loose smut has been observed throughout many areas of the grainbelt and a proportion of the seed being harvested this season will be infected.
In 2024, to minimise the expression of these smuts, it is advisable to replace highly contaminated seed with clean uninfected seed and treat seed with a registered seed dressing. For more information refer to DPIRD’s 2024 PestFacts WA Issue 18 article Smuts in cereals - this year and going forward.
Sclerotinia in lupin and canola
Sclerotinia stem rot in lupins and canola is caused by the same fungus (Sclerotinia sclerotiorum) and continues to pose a risk for 2025 crops. The incidence of this disease in lupins was particularly significant in the Geraldton and Kwinana North port zones this year. Even in areas where incidence in canola and lupin was lower than previous seasons, the risk for 2025 remains high due to the disease inoculum (sclerotia) surviving in paddocks from previous high disease years. Sclerotia have been found to survive for at least 6 years in soil and stubble, so careful consideration should be given to paddock rotations. Sclerotinia can infect most broad leaf crop and pasture species but not cereals, making cereals a suitable break crop for the disease.
To read about earlier sclerotinia activity this season, refer to the 2024 PestFacts WA Issue 15 article Basal sclerotinia stem rot in lupins and vetch.
Blackleg in canola
Blackleg is stubble-borne so it is crucial to avoid sowing a canola crop into last year’s canola stubble. Evaluate different blackleg canker strategies pre-sowing by using the DPIRD BlacklegCM tool. For more information refer to DPIRD’s upcoming 2025 WA Crop Sowing Guide and GRDC’s Blackleg Management Guide.
Further information
For more information on crop foliar diseases contact Plant pathologists Geoff Thomas in South Perth on +61 428 947 287, Ciara Beard in Geraldton on +61 8 9956 8504, Andrea Hills in Esperance on +61 8 9083 1144 or Kithsiri Jayasena in Albany on +61 8 9892 8477.
For more information on crop viruses contact Virologist Benjamin Congdon in Perth via Benjamin.Congdon@dpird.wa.gov.au.
For more information on crop soil borne diseases contact Senior Nematologist Sarah Collins in Perth on +61 8 9368 3612, Plant Pathologist Daniel Hüberli in Perth on +61 8 9368 3836 or Research Scientist Carla Wilkinson in Perth on +61 8 9368 3862.
Article authors: Ciara Beard (DPIRD Geraldton), Andrea Hills (DPIRD Esperance) and Geoff Thomas (DPIRD Perth).
Article input: Kithsiri Jayasena (DPIRD Albany) and Benjamin Congdon (DPIRD Perth).