Stripe rust in wheat

Stripe rust (Yellow 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 veins. The spores occur on the upper surface of the leaves, the leaf sheaths, awns and inside of the glumes. See photos of stripe rust in wheat.

Stripe rust requires cool and wet conditions to infect the crop. Free moisture on the leaves and an optimal temperature (10-15°C) are required for infection. Pustules erupt within 10-14 days after infection.

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 fungicides recommended for the control of stripe rust. Fungicides (Table 1) can be incorporated with the fertiliser or applied as seed dressings to delay the onset of disease. Later on if 'money' leaves require protection, recommended foliar fungicides (Table 2) can be applied for the control of stripe rust.

In Queensland, stripe rust pathotypes 134 E16 A+ and 134 E16 A+17+ were found prevalent during 2011. Grain growers should refer to the wheat varieties guide when selecting stripe rust resistant varieties as there is a threat from additional stripe rust pathotypes 134 E16 A+J+ and 134 E16 A+J+ T+ which have been identified in Queensland.

To request a copy of the Wheat Varieties Guide for Queensland, contact us.

Leaf rust in wheat

Leaf rust (Brown rust)

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

Leaf rust produces reddish-orange coloured spores which occur in small, 1.5 mm, circular to oval-shaped 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.

The spores require 15 to 20ºC temperature and free moisture (dew/rain/irrigation) on the leaves to successfully infect wheat. The first signs of the disease (sporulation) occur 10-14 days after infection. Removal of volunteer wheat plants, which forms a green bridge for the fungus through the summer, can eliminate or delay the onset of leaf rust.

View images of leaf rust in wheat.

Find out about the use of foliar fungicides to control leaf rust (Table 2).

Stem rust in wheat

Stem rust (Black rust)

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

Stem rust produces reddish-brown spore masses in oval, elongated or spindle-shaped pustules on the stems and leaves. Unlike leaf rust, pustules erupt through both sides of the leaves. Ruptured pustules release masses of stem rust spores, which are disseminated by wind and other carriers.

Stem rust develops at higher temperatures than the other wheat rusts within a range of 18-30°C. Spores require free moisture (dew, rain or irrigation) and take up to six hours to infect the plant and pustules can be seen after 10-20 days of infection.

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 grown, or a new stem rust pathotype has developed, which has overcome the wheat's resistance.

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.

• Photos of stem rust in wheat
• Foliar fungicides to control stem rust

Yellow/Tan spot in wheat

Yellow spot (Tan spot)

Tan-brown flecks turning into yellow-brown oval-shaped spots/lesions surrounded by yellow margins, may expand into 10-12 mm in diameter. Large lesions coalesce with dark brown centres. Spot develops on both sides of leaves. Temperature from 20ºC to 30ºC and free moisture favours disease development. In susceptible cultivars yellow spot can cause up to 30% yield losses. A break from wheat-on-wheat (crop rotation with non host crops) can reduce the risk of yellow spot. Sow resistant varieties and to request a copy of the Wheat Varieties Guide for Queensland, contact us.

• Foliar fungicides to control yellow spot (Table 2)
• Detailed information on yellow spot management is available from the Grains Research and Development Corporation website

Recommended fungicides

Table 1: Fungicides recommended for seed/fertilizer treatment

Diseases	Fungicides
	Fluquinconazole (167 g/L)	Flutriafol (250 g/L)
Stripe rust (Yellow rust)	Rate of product formulation: 450 ml/100kg seed	Rate of product formulation: 200 or 400 ml/ha Fertiliser
Leaf rust (Brown rust)	Rate of product formulation: 450 ml/100kg seed
Stem rust (Black rust)
Yellow spot (Tan spot)
Withholding periods after treatment	12 weeks for grazing and harvest	4 weeks for grazing and harvest

Table 2: Rate of fungicides (product formulation) recommended as foliar sprays for the control of yellow spot and rust diseases of wheat

Diseases	Foliar Fungicides
	Epoxi- conazole (125 g/L)	Flutriafol (250 g/L)	Propi- conazole (250 g/L)	Triadimefon (125 g/L)	Tebu- conazole (430 g/L)	Prothio- conazole (210 g/L) + Tebu- conazole (210 g/L)	Azoxy- strobin (200 g/L) + Cypro- conazole (80 g/L)	Propi- conazole (250 g/L) + Cypro- conazole (80 g/L)
Stripe rust (Yellow rust)	250-500 ml/ha	250-500 ml/ha	250-500 ml/ha	500 or 1000 ml/ha	145 or 290 ml/ha	150-300 ml/ha + Hasten 1% v/v	400 or 800 ml/ha	250-500 ml/ha
Leaf rust (Brown rust)	500 ml/ha	250-500 ml/ha	150-500 ml/ha		145 or 290 ml/ha	150-300 ml/ha + Hasten 1% v/v	400 or 800 ml/ha	150 - 500 ml/ha
Stem rust (Black rust)			500 ml/ha		145 or 290 ml/ha	150-300 ml/ha + Hasten 1% v/v		500 ml/ha
Yellow spot (Tan spot)			250-500 ml/ha		145 or 290 ml/ha	150-300 ml/ha	400 or 800 ml/ha	250-500 ml/ha
Withholding Periods	6 weeks for grazing and harvest	7 weeks for grazing and harvest	4 weeks for harvest, 7 days for grazing	4 weeks for grazing and harvest	5 weeks for harvest, 14 days for grazing	5 weeks for harvest, 14 days for grazing	6 weeks for harvest, 21 days for grazing	6 weeks for harvest, 21 days for grazing

Diagnosing leaf diseases in wheat

Disease	Spore colour	Symptoms	Plant part affected
Stripe rust	yellow/orange	Small closely packed circular pustules during the vegetative stage, becoming stripes along leaves of older plants (view stipe rust image)	Upper surface of leaf, leaf sheaths, awns and inside glumes
Leaf rust	orange/brown	Random, circular to oval pustules (view leaf rust image)	Upper surface of leaf and leaf sheaths
Stem rust	reddish/brown	Random, oblong pustules with torn margins (view stem rust image)	Both sides of leaf, leaf sheaths, stems and outside of head
Yellow spot	small tan (yellow brown) oval spots surrounded by a yellow margin	Spots up to 10 mm, varied shapes and may coalesce (view yellow spot image)	Both sides of leaf, leaf sheaths, stems and outside of head