Stripe rust in wheat.

Stripe rust

Photos of stripe rust in wheat.

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.

The 2009 winter season wheat variety guide was also posted to registered growers in February 2009. Printed and electronic copies of this guide are available - contact us on 13 25 23.

Stem rust in wheat.

Stem rust

Photos of stem rust in wheat.

Foliar fungicides to control stem rust.

Stem rust is caused by the fungus Puccinia graminis f. sp. tritici. In addition to wheat it can also attack barley, oats and rye.

Stem rust initially produces reddish-brown spore masses in oval or elliptical pustules with torn margins, 3x10 mm on the stems, the glumes and unlike leaf rust, on both sides of the leaves. Towards the end of the season the pustules become black as a different spore type is produced.

Queensland wheat varieties have reasonable resistance to stem rust (rating 5 or higher). However in the past, stem rust has had the ability to cause significant economic damage (50-100 % of yield). This has happened when conditions are conducive for the disease and susceptible varieties are used, or a new stem rust pathotype has developed, which has overcome the wheat's resistance.

Stem rust develops at higher temperatures than the other wheat rusts with 20°C as optimum and a range of 15-40°C. Spores require free moisture (dew, rain or irrigation) and take up to six hours to infect the plant. New infections produce their own spores 10-20 days later.

Inoculum must be present for the disease to develop. Practising crop hygiene, by removing volunteer wheat, which forms a green bridge for the fungus through the summer, can eliminate or delay the onset of stem rust.

As with all crop diseases, rusts continuously change, producing new pathotypes. These are detected when disease is found on a previously resistant wheat variety. Should stem rust be seen on a variety which was previously resistant please contact us on 13 25 23.

Leaf rust in wheat.

Leaf rust

Leaf rust is caused by the fungus Puccinia triticinia (previously called Puccinia recondite f. sp. tritici). The disease can also infect rye.

Leaf rust produces reddish-orange to reddish-brown spores which occur in small, 1.5 mm, oval pustules. These are found on the top surface of the leaves, distinguishing leaf rust from stem rust which is found on both surfaces of the leaf.

Queensland wheat varieties mostly have reasonable resistance (rating of MR-MS - 5 or higher) and so leaf rust is currently not of major concern to Queensland wheat growers.

Leaf rust develops at temperatures from 15-20ºC. The spores require free moisture (dew/rain/irrigation) on the leaves and close to 100 % humidity to successfully infect wheat. The first signs of the disease (sporulation) occur 10-14 days after infection.

Inoculum must be present for the disease to develop. Practising crop hygiene by removing volunteer wheat, which forms a green bridge for the fungus through the summer, can eliminate or delay the onset of leaf rust.

As with all crop diseases, rusts continuously change, producing new pathotypes. These pathotypes are detected when disease is found on a previously resistant wheat variety. Should leaf rust be seen on a variety which was previously resistant please contact us on 13 25 23.

View images of leaf rust in wheat.

Find out about the use of foliar fungicides to control leaf rust.

Foliar fungicides for controlling rusts

Table 2. Some registered fungicides and rates to control foliar diseases of wheat

Active ingredient and examples of trade names	Stripe rust	Stem rust	Leaf rust	Yellow spot
Flutriafol Flutriafol 250®Force fungicide®Impact®Jubilee®	R		R
Propiconazole Aurora 250 EC®Bumper 250 EC®Prestige®Propiconazole 250 EC®Slipstream 250EC Tilt 250EC®Tower 250EC®Tyrant®	R	R	R	R
Tebuconazole Folicur 430 SC®Orius 430 SC®Stingray®Tebuconazole 430 SC®	R		R	R
Triadimefon Accord®Bayleton 125 EC®Slingshot®Triad 125 EC®Triadimefon 125 EC®Turret®	R	R
Azoxystrobin + Cyproconazole Amistar Xtra®	R		R	R
Propiconazole + Cyproconazole Tilt Xtra®	R	R	R	R

® Denotes registered trade mark.
R Denotes registered in Queensland
    Consult label for dosage

The above information is given as a guide only. These products must be used strictly as directed and in accordance with all instructions on the label and in other current reference material. Fungicide registrations and recommendations change continuously. Always consult the label and adhere to the label recommendations. In particular observe dosage rates, timing of application, re-entry and withholding periods.

It is important to ensure the application equipment is in good working order and accurately calibrated. It is also important to ensure the fungicide has not exceeded its shelf life.

Foliar fungicides can give good control as long as they are applied early in the epidemic. Their effectiveness will depend on varietal susceptibility, level of infection and the stage of crop growth at application.

Diagnosing leaf diseases in wheat