Queensland, Australia
November 29, 2011

A leading plant pathologist warns grain growers should sequence their crops carefully to limit the impact of plant diseases emerging due to the increased use of pulses and summer crops in rotations.

Dr Malcolm Ryley, Agri-Science Queensland principal plant pathologist says summer crops grown in the Grains Research and Development Corporation (GRDC) northern region can harbour fungal diseases that can severely reduce yields in follow-up winter crops.

GRDC-supported research shows one of the most concerning disease links exists between sorghum and head blight of winter cereals, caused mainly by Fusarium graminearum.
“Past and recent findings suggest sorghum can play an as yet undefined role in the survival of Fusarium graminearum, so sorghum crops should not be planted into or near winter cereal stubble likely to be infected with the pathogen,” Dr Ryley said.

Maize is also an important host of F. graminearum, particularly on the Liverpool Plains and Dr Ryley says growers should avoid crop sequences which will put both maize and winter cereals at risk.

Dr Ryley said growers can also minimise the impact of the main pathogens responsible for sorghum stalk rot, Macrophomina phaseolina the cause of charcoal rot, and the Fusarium species, Fusarium thapsinum and Fusarium andihazi, through crop sequencing.

“Because of their ability to survive from season to season in infected stubble, the levels of the charcoal rot and fusarium stalk rot pathogens in a paddock will generally increase with consecutive sorghum crops.

“Where charcoal rot has been a problem, other susceptible crops like sunflower, dryland soybean and mungbean should be avoided in future crop sequences for at least three years to reduce charcoal rot levels, and serious consideration should be given to growing a series of winter crops in the crop sequence.”

Both Fusarium thapsinum and Fusarium andiyazi have a very narrow host range, so if the disease becomes an issue in a paddock, growing a sequence of non-hosts like winter cereals and broadleaf crops will reduce their impact on future sorghum crops.

Several Sclerotinia species are endemic in the northern region and can cause significant losses on both summer and winter broadleaf crops.

“These species can survive for many years as hard black sclerotia, so when Sclerotinia reaches yield-limiting levels in a paddock, the only rotation options are to change to sorghum, maize and the winter cereals,” Dr Ryley said.

The experiences with plant diseases in the northern region over the past year shows when favourable conditions occur, some pathogens can be found well outside their usual range.
“For example, while F. graminearum outbreaks on winter cereals are confined to cooler, wetter cropping areas like the Liverpool Plains in most years, it was found at significant levels in crops in southern Queensland during the 2010 winter growing season,” Dr Ryley said.

“Particular care in sequencing needs to be taken when there has been a significant outbreak of a disease in the previous crop.

“The first step in minimising the impact of the disease on future crops is to obtain an accurate diagnosis on its cause.

“In addition, knowledge of the host range of the causal pathogens and of the key aspects of their biology is vital when planning crop sequences in a particular paddock.”

GRDC’s Ute Guide series provides a first port of call for an initial diagnosis of summer-crop diseases, but expert help should be sought when the cause is not clear.

To find out more, visit www.grdc.com.au.
 

Website: http://www.grdc.com.au

Published: November 29, 2011