Epidemic reaches new heights

Researchers say this season"s stripe rust outbreak in eastern states will be a recurring risk while susceptible varieties are still grown. Kellie penfold reports

Researchers and plant pathologists are hoping the aggressive nature of this year"s stripe rust epidemic, particularly in NSW, will prompt many growers to rethink wheat variety choices for 2006.

Researchers say the continuing use of susceptible varieties is hindering their efforts to prevent epidemics, although they acknowledge the risk-management difficulties when susceptible varieties happen to be among the highest-yielding varieties. Having a range of fungicides on hand is no longer enough to justify growing such varieties, they say.

Season 2005 has taken stripe rust to new heights.

Peter Hamblin"s Agritech Research oversees four research projects on stripe rust, two of which are GRDC-funded, and interesting results are coming to light. "This is the worst year we"ve ever seen for stripe rust in southern NSW," he says. "It was seen earlier than ever before and, from early findings, it appears a lot of our product strategies - particularly pre-sowing - are not holding up as well as we thought they would.

"Such a vigorous and aggressive epidemic of stripe rust has taken people by surprise."

Mr Hamblin, who is based at Young and has trial sites across the Riverina, says the development of stripe rust in 2005 has made many farmers consider the disease more than just a seasonal aberration but a routine part of the farming program which needs strong management.

"By mid-October the skies across the Riverina were buzzing with planes applying fungicides - much of that on crops that had already received a presowing treatment as a seed or fertiliser dressing, or earlier foliar fungicide sprays.

"For many growers it turned out to be a three-spray season."

Dr Colin Wellings, principal research scientist at the Plant Breeding Institute, Cobbitty, NSW, says three fungicide applications indicate other control measures are needed. "In 2004, growers used more than $90 million worth of fungicide to treat stripe rust in cereal crops," he says. "It was $40 million in 2003. I would suggest, with the severity of the epidemic, it would be over the $90 million mark this year."

The potential loss to the grains industry of a serious epidemic has been estimated at up to $600 million. "So we need to concentrate on minimising the risk and it may mean some highly susceptible varieties have to go. H45Plant Breeder Rights icon is still grown by many farmers because of its high yield, but, put simply, H45Plant Breeder Rights icon may have to go to stop stripe rust."

Mr Hamblin says some of the most interesting findings are coming from comparisons of seed and fertiliser treatments: "We thought we knew everything about stripe rust, but we have learnt a lot more this year. And while the results will not be fully clear until after harvest, we are finding the seed and fertiliser treatments are not going the distance we thought they would."

For 2006, Mr Hamblin says management plans need to include eliminating the "green bridge" of potential host plants in self-sown wheat over summer, decreasing the amount of susceptible varieties grown, using a presowing treatment and then following up with a preventative foliar fungicide application when spraying for weeds in late winter/early spring.

"If an outbreak occurs, it could then be followed up with another fungicide application by ground or air," he says.

Growers, say researchers, need to be aware that a number of factors - good February rains, a mild winter and warm spring - "click" to cause an epidemic and this risk would be present each year due to self-sown susceptible host plants over summer, the continued use of highly susceptible varieties and some growers failing to treat stripe rust outbreaks adequately.

Dr Gordon Murray, principal research scientist (plant pathology) at the NSW Department of Primary Industries at Wagga Wagga, says the epidemic this year could be declared the worst because of its duration.

He says that while susceptible hosts have played a large role in the disease"s transmission, he also believes the epidemic has been aided by dual-purpose wheats that have been under-grazed or not grazed at all. "There was just so much inoculum - once it took off it was going to be hard to control," he says.

Dr Grant Hollaway, senior plant pathologist at the Department of Primary Industries Victoria, in Horsham, says his group started receiving reports of stripe rust in July. However, he says pre-sowing seed and fertiliser treatments in Victoria have largely succeeded. "It took pressure off growers who only faced further treatment decisions once rust was detected. The period of uncertainty is in that last four weeks of the season when you have to decide whether to spend the money for what may have been only a small yield loss." Some good news on stripe rust has been a significantly reduced impact in WA this season after a concerted campaign by the Department of Agriculture WA to decrease plantings of susceptible varieties and use pre-sowing treatments.

GRDC Research Code SFS00006
For more information: Dr Colin Wellings, 02 9351 8826, colinw@camden.usyd.edu.au;
Dr Gordon Murray, 02 6938 1879, gordon.murray@agric.nsw.gov.au;
Dr Grant Hollaway, 03 5362 2117, grant.hollaway@dpi.vic.gov.au;
Dr Robert Loughman, 08 9368 3691, rloughman@agric.wa.gov.au;
Peter Hamblin, 02 6382 6711, pjhamblin@agritech.com.au

Plant Breeder Rights icon Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994.