Growers warned: answer to stripe rust is in your hands
By Emma Leonard
The next outbreak of stripe rust is in growers" hands, according to district agronomists from around the country who met at Wagga Wagga, NSW, in December.
The meeting of 30 rust specialists, who met to review the 2003 epidemic, reported that breaking the "green bridge" between crops was the first essential step towards controlling the disease - and only growers can ensure this happens.
Wind spreads stripe rust inoculum over long distances and it can survive for up to five days without contact with a host plant.
It means that any stripe rust-susceptible volunteer wheat plants can act as an early host and a source of seedling infection. NSW Agriculture plant pathologist Gordon Murray said volunteers in paddocks or roadsides could be infected and carry the disease into next season: "Therefore the more volunteers that are controlled in late summer, the less inoculum is around to start next year"s epidemic," he said.
This has already been demonstrated by WA reporting little stripe rust in 2003 after a bad outbreak in 2002. Dr Rob Loughman, from the WA Agriculture department, attributed this to the farming community"s actions in ensuring that paddocks were free of volunteers by late summer, as well as the sowing of resistant varieties and the use of fungicides at sowing.
Dr Colin Wellings, NSW Agriculture"s stripe rust specialist at the Plant Breeding Institute, Cobbitty, said the 2003 epidemic was the first major outbreak of stripe rust in eastern Australia since 1984. Following this, stripe rust was controlled by growing resistant varieties.
A second introduction of stripe rust occurred in 2002, this time in WA, and was suspected as having arrived from North America on a traveller"s clothing. The WA race may then have blown across the Nullarbor late in 2002, leading to its detection in eastern Australia in the 2003 spring. By the end of the season it was widely distributed.
Agronomists say variety resistance only relates to adult plant resistance. Research in the 1980s suggested that resistance develops around mid-booting (GS 45). New work shows that it develops about five days later between GS 49-53.
This delay may be related to the higher levels of nitrogen now applied to most crops compared to the 1980s. Interestingly, stripe rust is the only wheat disease that shows such a marked difference in severity between different levels of nitrogen.
"Until susceptible varieties including H45 can be replaced, growers will need to use fungicides on most varieties to protect them from early epidemics of stripe rust," said Dr Wellings, who has completed a comprehensive reassessment of variety rating for stripe rust.
Growers are encouraged to refer to this information, which is available from state departments of agriculture and primary industry, and to select the variety with the highest level of resistance for their situation.
Fungicide use at seeding provides a vital back-up to variety resistance. The cheaper triadimenol seed dressings (eg Baytan®) only provide protection to the seedlings while more expensive treatments such as the seed-applied fl uquinconazole (eg Jockey®) and fertiliserapplied flutriafol (eg Impact-in-furrow®) provide longer protection and may remove the need for foliar fungicide applications later in the season.
In-crop fungicide guidelines are being developed and will be publicised during autumn and winter in time for the possible spring epidemic.
"The severity of the spring epidemic will depend on the whole farming community response to the control of the green bridge in late summer/early autumn 2004, and their general use of effective seed or fertiliser fungicide treatments to control stripe rust in young crops," said Dr Wellings. "If the area sown to susceptible wheats can be reduced in 2004, this will reduce the disease risk in 2005."
For more information:
Dr Gordon Murray, 02 6938 1879, fax 02 6938 1822, email@example.com
GRDC RESEARCH CODES DAN474 & US315, programs 1 and 3