Bio control can tame terrible two: Take all and Rhizoctonia

Researcher David Roget assessing wheat for the root disease take-all.

'Good' microbes are overpowering 'bad' microbes and controlling two major cereal root diseases on a farm in South Australia's lower north where an experiment has been underway for 16 years.

"Earlier this year we announced that, since 1983, in both cultivated and direct drilled treatments where stubble had been retained, Rhizoctonia had fallen to negligible levels," said experimental scientist with the Cooperative Research Centre for Soil and Land Management and CSIRO Division of Soils, David Roget.

"Now we can confirm the same thing has happened with take-all."

The diseases annually cost graingrowers more than $100 million in lost production in the southern and western grainbelt.

Trials on Robin Manley's Avon property, where stubble has been retained since 1979, are showing biological suppression of these diseases over the long term. The trials have been supported by growers through the GRDC.

"These results have not been reported anywhere else in the world and are changing the way we think about diseases and their control," said Mr Roget.

"The reason for disease suppression is not fully understood but is most likely due to increased biological activity in the soil related to long-term stubble retention."

Mr Roget said take-all was regarded as the most important cereal root disease across southern Australia. Annual loss estimates are $80 million. The take-all fungus attacks the roots of plants, blocking water and nutrient carriage to other parts of the plant. There are often no above-ground symptoms.

Methods of controlling take-all

Current control methods include the use of non-host crops such as grain legumes or oilseeds and by grass removal from pastures in the year before sowing. (See related story next page on grasses and take-all.) These techniques provided good control of take-all in high rainfall areas (more than 350 mm a year) but are less appropriate in regions with lower rainfall because of the lack of suitable break crops.

Mr Roget said there are no take-all resistant wheat or barley varieties. The Avon research incorporated a number of two-year rotations as well as the direct drilled and cultivated treatments.

Suppression of the diseases occurred in all tillage and rotation treatments.

The researchers found that Rhizoctonia root damage increased in the first four years of the trials and then fell steadily to negligible levels by 1990

For take-all, the first indications of suppression occurred around 1987. By 1989 disease levels were minimal and have stayed that way.

"This year we could not find one plant in the trial with take-all on the roots," said Mr Roget. He said work will now focus on generalising these results to southern dryland conditions.