Mild end-of-season conditions and frost damaged crops have contributed to a higher risk of stripe rust for most of the grainbelt next season.

Department of Agriculture, Western Australia plant pathologist Geoff Thomas said the risk of stripe rust, and potentially stem rust, coming out of the 2005 season was greater than at the same stage in 2004.

Mr Thomas said the stripe rust risk in the northern agricultural region should be lower than other areas of WA, and similar to recent seasons, unless summer and autumn rainfall activity directly affects the region.

The potential for rust outbreaks in 2006 should be considered as part of overall variety choice in conjunction with strategic pre-season fungicide use. 

“Continuing cool and damp conditions during October-November have prolonged the growing season in many areas of the wheatbelt,” Mr Thomas said.

“These conditions have allowed continued infection by cereal rust diseases, including stripe rust.  As a result, despite a delayed appearance, late stripe rust infection was widespread and ongoing late into the season, providing a background of inoculum for the 2006 season.

“In general, seasons with soft finishes followed by summer or autumn rain will favour the survival of rust inoculum and increase risks associated with early widespread rust infection in the following season.  The presence of late rust infection, can provide opportunities for greenbridge carry-over of rust if we get summer and autumn rainfall.”

Mr Thomas said the start to the 2005 season was characterised by a long dry period over summer, lasting from the early finish to the 2004 season through to the end of March this year. As predicted this long dry spell was unfavourable for carry-over of rust diseases and consequently rust occurrence in 2005 was around six weeks later than 2004.

By that stage most crops that became infected were after flag leaf emergence, when adult plant resistance of intermediate varieties was developing.

Mr Thomas said this season’s frost damaged crops could also increase the risk from rust survival in summer. 

“In some areas frost affected crops have re-shot, producing late green host plants for rust to survive on into the start of summer,” he said.

“Growers can address some of the risks by reducing plantings of very-susceptible and susceptible varieties to minimise the early incidence of infection, the rate of epidemic development and yield losses from outbreaks next season.  

“Where possible, very susceptible varieties should be avoided or at the very least managed with preventative strategies to address rust risk.  These include use of appropriate seed dressing or in-furrow fungicides which have been proven to delay the onset of rust infection.

“The majority of initial stripe rust reports during recent seasons and in 2005 came from the most susceptible varieties without fungicide protection.”

Mr Thomas stressed that paddocks where susceptible varieties were grown in 2005 should be actively managed over summer and autumn by preventing the development of green-bridge conditions with herbicide or grazing management.

Regular updates of plant disease risk including maps outlining regional rust risk are available from the ‘Plant Disease Forecast’ page on the Department of Agricultures website.