Managing stem rust of wheat

Pre-season management

Remove summer volunteers that created the green bridge

Self-sown summer and autumn volunteers (predominantly wheat and barley), which help to produce the green bridge, should be killed with herbicides or heavy grazing as soon as they develop and at least four weeks before crop sowing. This will reduce local carryover of rust spores and reduce the risk of early infection. For more information refer to Control of green bridge for pest and disease management.

Sow resistant varieties

Sowing varieties with resistance to wheat stem rust is encouraged in Western Australia, particularly in years where rust risk is high and in rust prone environments. Varieties that are partially or fully resistant to rust are effective in reducing disease build-up and preventing losses. In rust-prone environments or high-risk seasons it is very important to avoid susceptible and very susceptible varieties. Use the Wheat variety guide for Western Australia to identify varieties with some resistance to stem rust.

Spring management

Paddock monitoring

Warming spring conditions favour stem rust so the disease becomes apparent after flag leaf emergence. When stem rust risk exists (such as in green bridge areas or after reports of stem rust in your region):

• monitor susceptible crops at 7-14 day intervals from flag leaf emergence to early dough grain development.
• inspect different parts of the crop by carefully examining plants (especially lower stems) for signs of stem rust infection.
• if stem rust is found, walk through the paddock in a 'W' pattern and collect 100 random stems from the crop (that is, 10 stems from 10 locations) and determine the number of stems with any stem rust.
• the MyCrop app can assist you to diagnose crop diseases
• if you need further help with diagnosis, a chargeable diagnostic service is available through AGWEST Plant Laboratories. Send 6-10 infected stems or leaves to: AGWEST Plant Laboratories, Department of Agriculture and Food, Western Australia, Locked Bag 4 Bentley Delivery Centre WA 6983. Post in a paper envelope (no plastic) with date, location, name, and contact details. Broadacre diagnostic submission forms are available from your local DAFWA office or via the AGWEST Plant Laboratories page.
• to monitor rust strains in Western Australia, growers and consultants are encouraged to send rust samples at no cost to the Australian Rust Survey, particularly from varieties showing unusually high levels of rust. Sampling instructions and dispatch forms are available from the University of Sydney page. Post samples in paper envelopes to University of Sydney, Australian Rust Survey, Reply Paid 88076, Narellan NSW 2567.

Foliar fungicides

Where wheat stem rust occurs in susceptible varieties, economic control can be achieved with fungicide applied at early disease onset. Economic responses result from improvements in yield and in grain quality (reduced screenings, increased hectolitre weight). A range of fungicide active ingredients are registered in Western Australia for stem rust control. For more information refer to Registered foliar fungicides for cereals in Western Australia.

Application of a registered foliar fungicide can effectively control stem rust. Early disease detection is important as experiments show that fungicide reduces subsequent rust severity on plant parts that were only slightly infected at the time of fungicide application, but is not effective on plant parts that were more heavily infected when treated. The degree and duration of control depends on the application rate. Control is more effective if the fungicide is applied early in the development of the disease (Table 2). The disease becomes more difficult to control as it progresses. Poor control is likely at rates below those recommended, particularly when disease levels are high. Under high disease levels, high rates should be used.

¹ Any stem rust detected on stem or leaves from each of 100 tillers.

Strategies for using fungicides to manage rust depend on when the disease starts and the level of risk acceptable to the grower. All strategies assume that rust is detected soon after the start of the epidemic. Monitoring susceptible crops is essential to achieve this.