August 9, 2004
From: EZ Grain [edited]
<http://www.ezigrain.com.au/news/News.asp?NewsID=57968&NewsCategoryID=1>

Early stripe rust alert for 2004

The first case of stripe rust has been found at a property in New South Wales, while another reported infection in SA's southeast is yet to be confirmed. According to new data from the Plant Breeding Institute's Cereal Rust Laboratory, in Sydney, several late winter crops have been infected.

Tests revealed on 30 Jul 2004 that a property near Grenfell, in NSW, was infected. Out-of-season wheat fields at Naracoorte (samples from late March) and Horsham in Victoria (from early April) were considered to be infected with wheat stripe rust but are still being tested.

The outbreak follows a severe stripe rust epidemic in 2003, when the WA strain of rust crossed into the eastern grain growing region for the lst time. The affected NSW crops of Whistler and Diamondbird are in southern NSW, west of Grenfell. Rust samples were received at Wagga Wagga Agricultural Institute on 3 Aug 2004, and the diagnosis was confirmed by Dr Gordon Murray, of NSW Department of Primary Industries.

Dr. Murray said the infection in the Diamondbird crop occurred in the last 3 weeks. Disease control options for this initial outbreak included grazing the Whistler field, and possibly combining a relatively inexpensive fungicide with a post-emergent herbicide on the Diamondbird paddock.

The Whistler crop was sown on February rain and, in contrast to a majority of early sowings of this variety in central and southern NSW, survived the ravages of locust grazing. When stripe rust was observed in Whistler, the crop was tillering and infection was not difficult to find. An adjacent field of Diamondbird at the 3-4 leaf stage was also noted to be infected.

"While it is recognised that protection of the flag leaf is important, the early onset of stripe rust may give cause to consider the application of cheaper fungicides in the node to tillering stages," Dr Murray said. "This should provide disease control in the late winter period, and leave open the possibility of a later application of more expensive fungicides for flag leaf protection when grain yield potential is somewhat more predictable."

[Stripe rust is caused by the fungus _Puccinia striiformis_ [Ps]. A major development in the stripe rust situation in Australia was the arrival of a new race/strain of Ps from overseas in 2002. 2 theories have been developed to explain the occurrence of the new strain. One suggestion is that Ps blew into Western Australia late in 2001 on wheat and the disease was not noticed until the 2002 crop year. High-altitude jet streams at speeds approaching 300 km/h are known to carry rust spores to Australia from wheat farms in Europe, Asia, and North America. Another route could be via an air passenger from France whose Ps-contaminated clothing touched wheat plants in a wheat field.

The impact of Ps-WA is that the fungus was blown onto eastern Australian wheat fields where it overcame stripe rust resistance in several popular wheat cultivars in eastern wheat fields. Presence of Ps-WA in eastern Australia means that the popular H45 wheat cultivar will have to be discarded along with advanced lines based on this cultivar. Provision of a new commerically acceptable resistant cultivar could take 5-10 years. I await receipt of information on the identity of the Ps isolate in South Australia and Victoria from our Australian colleagues.

Useful references:
<http://www.grdc.com.au/growers/gc/gc49/striperust.htm>
<http://www.ezigrain.com.au/news/News.asp?NewsID=57968> - Mod.DH]