Green bridge management over summer
Growers need to consider potential disease carryover into the 2023 season if wet conditions are experienced during summer 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, such as cereal rusts and powdery mildew, 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.
Rust spores are wind dispersed and can easily spread from one end of the grainbelt to the other. This year, wheat powdery mildew was prevalent across the wheatbelt and wheat leaf rust in many parts of the Geraldton port zone. If there is a wet summer and autumn in 2023 then inoculum of these diseases may be carried into the new cropping season.
Disease management strategies for 2023
To minimise this risk growers are encouraged to monitor:
- This year’s crops before harvest to see what diseases are present
- 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 to reduce potential pest and disease outbreaks.
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 the weeds and volunteers should be sprayed with a herbicide at least four to six weeks before sowing, to ensure weeds are completely dead at planting.
Alternatives to herbicides are to heavily graze or cultivate weeds and crop volunteers which will reduce their potential as a ‘green bridge’ or host of diseases and pests.
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 susceptible soils that are prone to erosion.
In addition to managing the green bridge growers can;
• Sow clean seed. Use certified seed treated with seed dressing fungicide that provides protection from at least smuts and bunts. Seed can be tested for fungal pathogens 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 2023 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.
• In case of early disease outbreak, budget for early foliar fungicide sprays where upfront fungicides are not used. For more information visit the department's Registered foliar fungicides for cereals in Western Australia.
• Reduce exposure to stubble borne diseases through rotation and careful paddock planning (to avoid sowing on or adjacent to infected stubble) or stubble management (such as grazing, windrowing, baling, incorporating 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, or at 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.
Sclerotinia in lupin and canola
Sclerotinia stem rot in lupins and canola is caused by the same fungus (Sclerotinia sclerotiorum) and both diseases were found across the WA grainbelt in 2022 though at much lower levels than 2021. Sclerotinia can also infect most broad leaf crop and pasture species but not cereals, making them a suitable break crop for the disease.
The disease inoculum, sclerotia, that are not harvested with seed, can survive for up to six years in soil and stubble. Growers are advised to carefully consider paddock rotations and use clean lupin and canola seed in 2023.
For more information on crop diseases contact Plant pathologists Geoff Thomas, South Perth on +61 (0)8 9368 3262, Ciara Beard, Geraldton on +61 (0)8 9956 8504, Andrea Hills, Esperance on +61 (0)8 9083 1144 or Kithsiri Jayasena, Albany on +61 (0)8 9892 8477.
For more information on crop viruses contact Virologist Benjamin Congdon, South Perth on +61 (0)8 9368 3499.
Article authors: Ciara Beard (DPIRD Geraldton) and Geoff Thomas (DPIRD South Perth).
Article input: Benjamin Congdon (DPIRD South Perth).