Southern crop disease threat

Growers are being warned to control the green bridge and choose disease-resistant varieties, after recent detections of wheat stem rust, barley leaf rust and powdery mildew on regrowth in 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 WA (DAFWA) researcher Kith Jayasena said the detection of significant amounts of wheat stem rust this year was of particular concern, because 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 re-growth, which was present in many areas of the lower Great Southern region.

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

Dr Jayasena said he had conducted fungicide trials in 2011 that highlighted the massive yield losses 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 (PBI), said suspected rust samples should be posted to the Australian Cereal Rust Control Program's 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 to the sender and the regional pathology team," he said.

"It is important to watch for any changes in rust pathotypes that 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 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 rust outbreaks."

Post suspected rust samples to Cereal Rust Survey, Plant Breeding Institute, Private Bag 4011, Narellan, NSW 2567. Samples should be placed in paper envelopes (do not use plastic wrapping or plastic-lined packages) and include the sender's name and email address.