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Early Rust Findings Prompt Green Bridge Warning

24 February 2012

AUSTRALIA - Growers are urged to control the ‘green bridge’ now and choose disease resistant crop varieties, after wheat stem rust, barley leaf rust and powdery mildew were found in Western Australia’s southern cropping regions.

The fungal diseases, capable of spreading long distances via spores, were found in barley regrowth at Green Range and Wellstead in the lower Great Southern, and in the Esperance region.

Department of Agriculture and Food (DAFWA) researcher Kith Jayasena, whose research is supported by the Grains Research and Development Corporation (GRDC), said the detection of significant amounts of wheat stem rust this year was of particular concern as the disease could cause yield losses of up to 90 per cent in susceptible wheat varieties.

“To see so much regrowth infected by disease this early in the year means that 2012 cereal crops will be threatened unless the green bridge is eliminated and resistant varieties are grown,” he said.

“If the weather remains warm and the green bridge is not controlled, we will see stem rust infecting susceptible wheat varieties in the coming season.”

Dr Jayasena said barley was a host for wheat stem rust and the infection he observed was in barley regrowth which was currently present in many areas of the lower Great Southern region.

“All WA growers should get rid of the green bridge (cereal regrowth) now, preferably by using a knockdown herbicide, or otherwise by grazing, and choose resistant varieties to seed in 2012,” he said.

Dr Jayasena said fungicide trials he conducted in 2011 highlighted the massive yield losses that susceptible wheat varieties could incur from wheat stem rust.

“The trials also identified the importance of identifying and responding early to wheat stem rust in susceptible varieties to minimise losses in yield and grain quality,” he said.

Dr Jayasena said the best economic returns for stem rust control were achieved when two foliar sprays of tebuconazole were applied - when wheat stem rust first became evident, and three weeks later.

“This strategy, when applied in trials in the high yielding environment of Gibson in the Esperance region, provided yields 56 per cent greater than the unsprayed crop, and economic returns of $399 per hectare – compared with $83/ha from a single fungicide application at the first sign of the disease, and $111/ha for a single spray three weeks after the disease becomes evident,” he said.

Dr Jayasena said growers planning to grow susceptible varieties this year should budget for the possibility of needing to apply fungicide to manage stem rust.

Associate Professor Colin Wellings (on secondment from the NSW Department of Primary Industries) at the University of Sydney’s Plant Breeding Institute, said suspected rust samples should be posted to the Australian Cereal Rust Control Program’s (ACRCP) Cereal Rust Survey as soon as possible.

“Analysis of the samples will confirm the type of rust and the pathotype, and this will be reported promptly and directly to the sender and the regional pathology team,” he said.

“It is important for us to watch for any changes in rust pathotypes which can cause rust to become virulent against particular resistance genes, and it is particularly important to know what pathotypes are present in the very early stages of a potential rust season.

“In the event of any resistance genes breaking down, we can issue a warning to industry so growers are aware of varieties containing these genes, and they can be prepared with foliar fungicides to control any rust outbreaks.”

The ACRCP consultative committee has developed a Rust Bust checklist to help growers be prepared for rust:

  • Grow varieties with adequate resistance to stem, stripe and leaf rust.
  • Phase out very susceptible (VS) or susceptible (S) varieties from your rotation wherever possible. Otherwise develop a rust management plan.
  • When selecting varieties, ensure you have a rust management strategy, including green bridge control and budget for intended fungicide use.
  • Know the seedling and adult plant rust resistance characteristics of the varieties you decide to grow, and identify whether they require chemical support.
  • Remove the green bridge (volunteer plants) at least four weeks before the intended sowing date.
  • Closely monitor crops to enable early rust detection and management.
  • Use appropriate fungicide support to maximise crop performance and minimise disease build-up.
  • Talk to your neighbour about your rust situation so management can be tackled more efficiently and be aware of the developing rust situation in your region.
  • Monitor the regional media and DAFWA PestFax to be aware of regional rust outbreaks.

TheCropSite News Desk

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