AgMemo - Grains news, December 2017

Page last updated: Thursday, 7 December 2017 - 10:37am

Please note: This content may be out of date and is currently under review.

Monitor 'green bridge' to maximise 2018 crops

Wheat plants growing amongst wheat stubble
Volunteer wheat can become a ‘green bridge’ leading to increased risk of crop disease.

The Department of Primary Industries and Regional Development (DPIRD) is urging grain growers to monitor green bridge to minimise insect pests and plant diseases in crops in 2018.

Wet conditions during summer can result 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 was found from Yuna to Esperance, and barley leaf rust and powdery mildew (in wheat and barley) were common in central and southern crops.

If there is a wet summer and autumn in 2018 there is a risk that the inoculum of these diseases may be carried into the new cropping season.

In addition to reducing disease risk, controlling summer weeds and volunteers aids in subsoil moisture and nutrient retention.

Disease management strategies for 2018

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 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 herbicide at least four to six weeks before sowing, to ensure weeds are completely dead at planting.

Alternatives to herbicides include heavy grazing or paddock cultivation which will reduce the potential of weeds and crop volunteers as a green bridge.

In addition to managing the green bridge, growers can take the following actions.

Treat seed

Loose smut was widely seen in 2017 especially in the southern and the central regions of the Wheatbelt. If crops were smutted, then treating seed with a premium type fungicidal seed dressing (and slowing augers down when applying it) is recommended for 2018.

Disease ratings

Know the latest disease ratings of varieties and plan accordingly. Choose adult plant resistant varieties. Crop variety guides detail the disease susceptibility for each variety. These are available for all grains by searching the DPIRD website.


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.

More information can be found at;
Control of green bridge for pest and disease management (DPIRD website)
Green Bridge fact sheet (Grains Research and Development Corporation).
Crop diseases: forecasts and management (DPIRD website)

For more information on crop diseases contact
Plant Pathologists
Kithsiri Jayasena, Albany on +61 (0)8 9892 8477
Geoff Thomas, South Perth on +61 (0)8 9368 3262
Andrea Hills, Esperance on +61 (0)8 9083 1144
Ciara Beard, 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.