Growers are urged to monitor green bridge to minimise insect pest and plant diseases in crops in 2018
Growers need to consider potential disease carryover into the 2018 season if wet conditions are experienced during summer resulting in weed and crop regrowth. This vegetation can serve as a ‘green bridge’ for diseases which need a living plant to survive, such as cereal rusts and viruses.
Rust spores are wind dispersed and can go through several cycles during the cropping season. This year, wheat leaf rust was found from Yuna to Esperance, and barley leaf rust and powdery mildew (wheat and barley) were common in central and southern areas. Barley and wheat volunteers can act as a ‘green bridge’ during a wet summer and autumn carrying inoculum of these diseases into the new cropping season.
Weed and crop volunteers can also act as a between-season host for 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.
Disease management strategies for 2018
Growers need to monitor the 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. Loose smut widely seen in 2017 especially in the southern and the central regions of the wheatbelt. Therefore using certified seeds treated with seed dressing fungicide is recommended for 2018.
- Get to 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 DPIRD website, which document 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, 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 the department's Control of green bridge for pest and disease management page and the Grains Research and Development Corporation's (GRDC) Green bridge fact sheet.
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 or Ciara Beard, Plant Pathologist, Geraldton on +61 (0)8 9956 8504.