Stem Rust of Wheat

Note Number: AG1251
Published: June 2005
Updated: April 2009

 

 This Agnote provides Victorian growers with information on the management of stem rust in wheat.

Stem rust in Victoria

Conditions that favour stem rust epidemics are rare and occur on average once every 16 years in Victoria . However, when conditions are conducive, the disease can cause complete crop loss in susceptible varieties. Historically, the most severe epidemics in Victoria occurred (in descending order of severity) in 1973, 1947, 1934 and 1955. In 1973, stem rust reduced the Victorian wheat harvest by 25%. It is unlikely that stem rust losses will ever be as severe as in 1973 due to the increased cultivation of stem rust resistant varieties, and the greater availability of effective foliar fungicides. In recent years, there have been few localised occurrences of stem rust.

What to look for

Stem rust is characterised by reddish-brown, powdery, oblong pustules. The pustules have a characteristic torn margin and can occur on both sides of the leaves, on the stems and the glumes. Stem rust spores are much darker in colour than stripe rust spores, which are yellow (Figure 1). As the plant matures, the pustules produce black spores known as teliospores. They occur mainly on the leaf sheaths and stem.

Conditions favourable to stem rust

Stem rust can occur in all regions of Victoria where susceptible varieties are grown. However, the likelihood of a stem rust epidemic is increased by several factors including:

• The build up of stem rust inoculum on volunteer wheat before sowing, both locally and in neighbouring states.
• The widespread planting of susceptible varieties.
• Favourable weather conditions, which includes good spring rains and warm (15-30 o C) humid conditions. If the two requirements above are met and there is a wet spring, an outbreak is likely to occur.

Pre-season management of stem rust

Stem rust can be managed using an integrated approach. This includes reducing the amount of inoculum in a district by managing the green bridge, avoiding susceptible cultivars and closely monitoring with a view to fungicide applications.

Green bridge

Rust can only survive from one season to the next on living plant material (mainly self sown cereals). Therefore, the removal of the ‘green bridge' is essential to reduce the amount of inoculum present to infect a new crop. This is why stem rust epidemics have been worse following wet summer/autumns that favour volunteer cereal growth.

Variety selection

Sowing resistant varieties provides the best protection against stem rust. In most parts of Victoria stem rust has been controlled because of the use of resistant wheat varieties.

Stem rust occasionally produces new pathotypes (races) which are capable of attacking resistant varieties. These new pathotypes occur when a chance mutation occurs in this asexually reproducing fungus. Use of resistant varieties minimises the amount of rust in a district, thus reducing the chance of new pathotypes occurring. It is important that growers are aware of a varieties resistance reaction to stem rust. For a comprehensive list of varieties, consult a current Agnote “Cereal Diseases Guide (AG1160)”.

In crop management of stem rust

The effects of stem rust can be minimised with the timely application of foliar fungicides. As there is limited information on the management of stem rust in Victoria , the following recommendations for the in-crop management of stem rust are based on experience in Western Australia .

Monitoring

Stem rust is most severe in susceptible varieties when it begins to develop in the crop before flowering and crop losses of 50% are possible. Yield losses from later infections are possible, but not as severe.

As stem rust requires warmer conditions than stripe rust for development, it is advisable to begin monitoring for stem rust from flag leaf emergence onwards. Monitoring will be necessary in seasons when stem rust has been detected locally, or on volunteer plants before sowing.

Guidelines for monitoring for stem rust in wheat crops:

• Inspect wheat crops every 7 to 10 days from flag leaf emergence to early dough grain development. However, if stem rust is detected within a region, then increase inspection frequency to every 4 to 7 days.
• Carefully inspect different plant parts, especially the lower stems, for symptoms of stem rust. Spend at least 15 minutes walking through each wheat crop.
• If stem rust is detected, walk through the paddock in a ‘W' pattern and collect 10 stems from 10 random locations (total 100) to determine the percentage of stem rust infection. See Table 1 for control options.

When to spray

The information in Table 1 is a guide for the application of foliar fungicides. Note that this table is not based on Victorian data, but on limited experimental data from Western Australia . Fungicides will give better control of stem rust when applied early in the epidemic. A late, low level occurrence of stem rust (ie after mid-dough) will have little impact on yield.

Choice of fungicide

In Victoria there are 3 active ingredients (available in a range of products) registered for control of stem rust. They are tebuconazole (e.g. Folicur® 430SC), propiconazole (e.g. Tilt® 250EC, Bumper®) plus combinations like cyproconazole and propiconazole (e.g.Tilt® Extra). Read the label before use, check that the product is registered and use the maximum recommended label rate for stem rust control in wheat.

Table 1. A guide for fungicide control of stem rust

Crop growth stage	% stems infected (a)	Resistance rating
		MS-S	MR-MS
Before ear emergence	1-5	Spray	Monitor
	>5	Spray	Spray
Ear emergence – mid dough	>5	Spray	Monitor
	>50	Spray	Spray
After dough stage, and 4 weeks grain filling left	>50	Spray	Spray

(a) Stems selected in a W pattern across crop.

Life cycle

Stem rust (caused by the fungus Puccinia graminis), can only survive from one season to the next on a living host. It does not survive on stubble, seed or soil. The most important hosts are susceptible wheat, but it can also survive on barley, triticale, and some grasses. Carry over on wheat from one season to the next is greatest during wet summer/autumns.

Rust spores are wind-blown and can be spread over large areas in a short time. Wet conditions and temperatures of approximately 15-30°C favour the establishment of stem rust within crops. Stem rust usually becomes evident later in the season than stripe rust.

Further references

More detailed information can be obtained from the DPI Information Note Series: www.dpi.vic.gov.au/notes

Cereal Diseases Guide (AG 1160).

Wallwork H (2000) Cereal Leaf and Stem Diseases.

Beard et al. (2006) Managing Stem Rust of Wheat. AgWA Farmnote No 73/2004. www.agric.wa.gov.au

Acknowledgements

This agnote was developed by Grant Hollaway June 2006.

It was reviewed by:

Frank Henry, Farm Services Victoria - BioSciences Research. March 2009.

This Agnote was prepared by Dr Grant Holloway with assistance from Frank Henry (DPI Horsham), and the National Cereal Rust Control Program (Cobbitty). Financial support by the GRDC is gratefully acknowledged.

Contact/Services available from DPI

DPI Field Crops Pathology, Grains Innovation Park , 110 Natimuk Rd , Horsham 3400 . Tel (03) 5362 2111, or the DPI Customer Service Centre 136 186.