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
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, firstname.lastname@example.org
GRDC RESEARCH CODES DAN474 & US315, programs 1 and 3