Growers are urged to monitor green bridge in 2019
Growers need to consider potential disease carryover into the 2019 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 Wheatbelt to the other.
This year, wheat leaf rust and powdery mildew were prevalent near Esperance and barley leaf rust was found on the south coast.
If there is a wet summer and autumn in 2019 then inoculum of these diseases may be carried into the new cropping season.
Disease management strategies for 2019
To minimise this risk, growers are encouraged to monitor any green bridge 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 kill weeds and crop volunteers, including those along fencelines, 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.
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.
- know the latest disease ratings of your varieties and plan accordingly. Use adult plant resistant varieties. Crop variety guides are available for all grains on the Department of Primary Industries and Regional Development (DPIRD) website, which detail 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 DPIRD'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 DPIRD'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, septoria 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 DPIRD'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 is caused by the same fungus (Sclerotinia sclerotiorum) that infects canola and both were found across the Wheatbelt in 2018.
Sclerotinia can also infect most broad leaf crop and pasture species but not cereals. So cereals can be used as a 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 2019.
For further disease forecasts and information on managing specific diseases in 2018 see the department's Crop diseases: forecasts and management.
For more information on crop diseases contact Kithsiri Jayasena, Plant Pathologist, Albany on +61 (0)8 9892 8477, Geoff Thomas, Plant Pathologist, South Perth on +61 (0)8 9368 3262 or Andrea Hills, Plant Pathologist, Esperance on +61 (0)8 9083 1144, Ravjit Khangura, Plant Pathologist on +61 (0)8 9368 3374 or Ciara Beard, Plant Pathologist, Geraldton on +61 (0)8 9956 8504. For more information on crop viruses contact Brenda Coutts, Virologist, South Perth on +61 (0)8 9368 3266.