Green bridge management over summer
Growers need to consider potential disease carryover into the 2024 growing season if wet conditions are experienced during summer and autumn resulting in weed and crop regrowth. This vegetation can serve as a ‘green bridge’ for diseases and pests which need a living plant to survive and are susceptible to issues 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.
This year, wheat leaf rust was prevalent in crops across the grainbelt. It may pose a risk to 2024 crops if inoculum is carried into next season on the green bridge. Many wheat varieties currently being grown in WA are rated as susceptible. Barley loose smut was also present and seed treatment may be necessary. Several reports of root diseases and plant parasitic nematodes, particularly rhizoctonia and root lesion nematodes, have been received from across the grainbelt, and management strategies are required to reduce potential yield losses in 2024.
Disease management strategies for 2024
To minimise green bridge risk, growers are encouraged to monitor the following:
- Check the PestFacts WA map for disease reports for their region in 2023. 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 2024. For further information on identifying and managing root diseases and nematodes see the previous 2023 PestFacts WA issue 16 article Why is my crop patchy? Diagnose soilborne diseases to form strategies for next season.
- Any green bridge that is present in summer and autumn for disease, 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 two weeks, free of vegetation capable of hosting disease or 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.
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 department’s Diagnostic Laboratory Services – Plant pathology services.
- Know the latest disease ratings of your varieties and plan accordingly. Use adult plant resistant varieties. The 2024 WA Crop Sowing Guide is 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 rusts, net blotches and powdery mildew in susceptible varieties, and rhizoctonia, crown rot and take-all. For more information see the department's Seed dressing and in-furrow fungicides for cereals in Western Australia.
- 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.
- Earlier sown crops may be more at risk of some 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 see the department's Control of green bridge for pest and disease management and the Grains Research and Development Corporation's (GRDC) Green Bridge fact sheet.
Barley loose smut
Barley loose smut has been prevalent throughout many areas of the grainbelt. Despite the dry spring conditions being less conducive for spread than the cool conditions during flowering in 2022, it is expected that some smut will have infected a proportion of the seed being harvested this season. In 2024, to minimise the expression of loose smut, it is advisable to treat seed with a seed dressing registered for loose smut. All registered seed dressings significantly reduce smut levels, but the SDHI products are the most effective. While all barley varieties can be affected, of our WA dominant varieties, Maximus CL has the smut susceptible variety LaTrobe in its pedigree, raising reasonable suspicion that it may also be susceptible. Spartacus CL is known to be very susceptible. For more information refer to DPIRD’s 2023 PestFacts WA Issue 15 article Barley loose smut - this year and going forward and Controlling barley loose smut page.
Sclerotinia in lupin and canola
Sclerotinia stem rot in lupins and canola is caused by the same fungus (Sclerotinia sclerotiorum) which poses a risk for 2024 crops. Although the incidence of this disease in crops was much lower in 2023 compared to previous seasons, the risk for 2024 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 them a suitable break crop for the disease.
To read about earlier sclerotinia activity this season, refer to the 2023 PestFacts WA Issue 13 article Sclerotinia stem rot update.
In 2023, lupinosis led to sheep illness and death in several regions due to Phomopsis-infected lupin stubbles or 2022 harvest seed consumption. Losses affected sheep grazing stubbles of several lupin varieties, including more resistant types. Both the 2021 and 2022 seasons were very favourable for Phomopsis infection of lupin and rainfall on mature infected stubble promoted growth of the fungus and production of mycotoxins.
While the 2023 season has been less favourable generally for fungal infection, the 2022/23 summer stock losses highlight lupinosis risk from lupin stubble grazing.
All lupin stubbles can be infected, however the risk of lupinosis is lower in more resistant varieties. Testing of isolates from 2022 paddocks has not detected any changes in lupin variety responses. Growers are urged to watch for the characteristic ‘leopard spotting’ Phomopsis symptoms in lupin stubbles, especially in susceptible varieties, desiccated crops or crops brown manured for fodder that have received spring/summer rain, and stubbles that receive abundant autumn rain. Stem and pod Phomopsis resistance ratings of lupin varieties can be found in DPIRD’s 2024 WA Crop Sowing Guide.
If you see unusual disease signs in your stock, call your private veterinarian or DPIRD field veterinary officer or the Emergency Animal Disease hotline on 1800 675 888.
For more information on crop foliar diseases contact Plant pathologists Geoff Thomas in South Perth on +61 (0)8 9368 3262, Ciara Beard in Geraldton on +61 (0)8 9956 8504, Andrea Hills in Esperance on +61 (0)8 9083 1144 or Kithsiri Jayasena in Albany on +61 (0)8 9892 8477.
For more information on crop viruses contact Virologist Benjamin Congdon in South Perth on +61 (0)8 9368 3499.
For more information on crop soil borne diseases contact Senior Nematologist Sarah Collins in South Perth on +61 (0)8 9368 3612, Plant Pathologist Daniel Hüberli in South Perth on +61 (0)8 9368 3836 or Research Scientist Carla Wilkinson in South Perth on +61 (0)8 9368 3862.
Article authors: Ciara Beard (DPIRD Geraldton), Andrea Hills (DPIRD Esperance) and Geoff Thomas (DPIRD South Perth).
Article input: Benjamin Congdon (DPIRD South Perth), Daniel Huberli (DPIRD South Perth), Sarah Collins (DPIRD South Perth) and Rod Thompson (DPIRD Northam).