Wheat Rusts - Stripe Rust (Yellow Rust)

Key points for Wheat Rusts

Reduce the risk of rusts in wheat by:

• Destroy volunteer wheat plants by March, which can provide a greenbridge for rust carryover
• Community efforts required to eradicate volunteers from roadsides, railway lines, bridges, paddocks and around silos
• Crop rotation is very important in case of yellow spot and Fusarium head blight
• Growing resistant varieties is an economical and environment friendly way of wheat production
• Seed or fertiliser treatment can controls stripe rust up to four weeks after sowing and suppress thereafter
• During the growing season active crop monitoring is very important for an early detection of diseases
• Correct diseases identification is very important; you can consult DPI fact sheets, charts, web site and experts. Collect samples in paper bags and send to LRC Toowoomba
• Deciding a fungicide spray, consider crop stage and potential yield loss
• Select a recommended and cost effective fungicide
• For proper coverage, the use of right spray equipment and nozzles is very important
• Read label, wear protective gear, be safe to yourself and environment
• Avoid repeated use of fungicides with same active ingredient in the same season
• Any disease outbreak, advise DPI, Call 132 523 or 07 3404 6999 or email web@dpi.qld.gov.au

Rust diseases occur throughout the wheat growing northern regions, frequently causing economic damage. In Queensland, in recent times, stripe rust has been the more important of these diseases.

Wherever possible, resistant wheat varieties MR (Moderately Resistant = 6) and above should be sown.

Rust fungi continuously change, producing new ‘pathotypes’. These pathotypes are detected when disease is found on a previously resistant variety. Even if a resistant variety has been sown, the crop should be monitored for foliar diseases on a regular basis. This should start no later than growth stage 32, the 2nd node stage on the main stem, and continue to at least growth stage 39, the flag leaf. This is because the flag leaf and the two leaves below it are the main factories contributing to yield and quality. It is very important that these leaves are protected from any diseases.

There are a number of fungicides registered in Queensland for the control of the rusts. Early intervention reduces damage to the important ‘factory’ leaves.

Stripe rust (Yellow rust)

Foliar fungicides to control stripe rust.

Stripe rust is caused by the fungus, Puccinia striiformis. It is easily distinguished from other wheat rusts by the orange-yellow spores, which produce small, closely packed pustules developing into stripes along the length of the leaf. The spores occur on the upper surface of the leaves, the leaf sheaths, awns and inside of the glumes.

Stripe rust requires cool, wet conditions to infect the crop. Optimum temperatures are 10-15°C for 4 hours and free moisture (dew/rain) on the leaves. Pustules erupt 10-14 days after infection.

The impact of stripe rust may be reduced by:

1. destroying the green bridge (volunteer wheat, triticale)
2. planting resistant varieties: moderately resistant = 6 (MR) and higher
3. applying seed dressings
4. applying foliar fungicides.

If the weather is conducive to stripe rust, the disease can cause up to 25% yield loss on varieties scoring moderately susceptible = 5 (MR-MS) or lower. This is provided there is inoculum from a neglected green bridge or from an infected crop.

There are several at-planting fungicides registered, which delay the onset of stripe rust. These are incorporated with the fertiliser or applied as seed dressings.

Note: Seed dressings and in-furrow treatments can shorten the coleoptile, the germinating shoot of the wheat plant.

This can reduce crop establishment, particularly when seed is sown deeply, in uneven seedbeds, or when seed is of poor quality, such as shrivelled seed.

There are a number of foliar fungicides registered for stripe rust control. Some of these also control the other rusts and yellow spot.

The current high wheat price has lowered the economic threshold for spraying, making it cost effective to spray at lower disease levels.

In Queensland, the prevailing pathotype is called the Western Australian or WA pathotype and has the code 134 E 16 A. Grain growers should refer to the Wheat Varieties for Queensland 2009 guide when selecting stripe rust resistant varieties as there is a threat from additional stripe rust pathotypes WA+YR17 and Jackie strains which have been identified in Queensland alongside the established Western Australian strain.