Yellow orange elongated pustules, full of powdery spores appear on the topside of the leaves in late winter to spring. The pustules are scattered on seedling leaves but tend to cluster into stripes along the leaf veins in older leaves. Occasionally the heads may be infected in severe infestations and there is a mass of spores when the glumes are pulled back. Seed may be shrivelled or aborted. It usually appears in paddocks as yellow patches that are 1-10 metres in diameter and spreads to the rest of the crop. The yellow orange spores will rub off the leaf onto your finger rubbed. The black spores at the end of the season don't rub off.
Wheat. Barley Grass is very susceptible to infection.
Cool, moist conditions with high humidity and temperatures between 8 and 150C favour infection and the development of the disease. Requires a living host to survive from one season to the next and won't survive on dead stubble or in the soil. Wheat and Barley Grass are good hosts. Spores do not survive in the soil or on stubble. Spread by wind over very large distances - possibly thousands of kilometres. Most resistant varieties are still prone to infection as seedlings. Resistant varieties may be susceptible to new strains of the Stripe Rust. Most resistant varieties are still susceptible as seedlings. The yellow orange spores are infectious whereas the black spores aren't. Spores will survive on clothing for at least a week.
Spores land on the leaf and germinate if conditions are moist and between 8 and 150C. They grow into the plant and about 14 days later the first pustules or stripes are seen. These expel spores to infect neighbouring plants. 2-4 weeks after the first pustules appear, areas of infection a few metres in diameter in the crop are noticed by growers.
Origin and History:
First found in central Victoria in 1979 and spread to Tasmania and new Zealand the following year. In 2002 a different strain was found in WA in 2002 near Newdegate and this strain had spread to the eastern states by 2003. It may have been introduced to WA from the USA by spores on contaminated clothing.
Initially patchy but often quickly spreads to the rest of the paddock
May cause significant yield losses in susceptible varieties. It can be the cause of reduced grain size, especially when it infects the heads. Early infections cause larger losses especially in susceptible(S) varieties.
Management and Control:
Sow resistant varieties. See Disease Susceptibility of Wheat Varieties. Use a seed treatment to reduce early infections. These typically give 8-12 weeks protection. "In Furrow" flutriafol or triadimefon based fungicides applied on the fertiliser or fluquinconazole based seed dressings usually provide the longest protection followed by triticonazole seed dressings then triadimenol or flutriafol based seed dressings and triadimenol based in furrow products. The length of protection usually depends on the rate of application. Some seed dressings may reduce crop emergence, which is made worse by deep planting and some pre emergent herbicides. Spray when yellow patches appear and repeat in 4 weeks if necessary. Spraying is unlikely to be economic after flowering of the Wheat. Control Barley Grass and volunteer or out of season Wheat. A number of decision aids have been produced to help choose varieties and spraying regimes.
When 20% of leaves show infection during tillering to jointing apply a fungicide within a week. Susceptible varieties - When 10% of leaves show infection after jointing apply a fungicide immediately and repeat in 14 days if necessary. Moderately susceptible varieties - If 15-20% of leaves show infection after jointing then immediately apply a fungicide immediately and monitor 14 days later for further spread. If rust is spreading then apply fungicide again. Moderately resistant varieties - If rust is spreading apply a fungicide. Resistant varieties - If rust is spreading then the strain of rust has probably mutated and the variety is no longer resistant to the disease. Treat as for moderately susceptible varieties. Consult Department of Agriculture notes for the current status of thresholds and current variety susceptibility ratings.
Related and Similar Species:
Leaf Rust of Wheat (Puccinia recondita) Stem Rust of Wheat (Puccinia graminis)
Computer aided decision aids are available for WA, Victoria and New South Wales.