Growers need strategy to manage yellow leaf spot
Southern Riverina and north-east Victorian grain growers will need to develop a strategy to manage yellow leaf spot before they plant this season’s wheat crop, according to a cereal diseases authority.
Greg Platz, Principal Pathologist, Agri-Science Queensland, advised the audience at a recent Grains Research and Development Corporation (GRDC) Grower Update at Corowa, NSW, that yellow leaf spot posed a risk to susceptible wheat varieties.
He said the fungus, which survives in crop residue and is favoured by frequent and extended periods of wet weather and temperatures between 10 and 30°C, is best treated through reducing infected stubble.
“When the new crop is sown into infected stubble and wet conditions prevail, mature ascospores are ejected onto the new crop and infection occurs,” Mr Platz said.
If the infection is left untreated, a susceptible wheat variety may measure yield losses of up to 65 per cent, Mr Platz said.
Triticale and rye are also susceptible to yellow spot.
In current farming systems, the emphasis has been on maximum retention of surface stubble, a system which also works in the favour of yellow leaf spot development, according to Mr Platz.
“With stubble retention it is a matter of when and not if yellow spot will become a problem.”
Continuous cultivation of wheat-on-wheat will lead to losses from yellow spot whenever favourable environmental conditions occur, Mr Platz said.
Mr Platz told the audience no control option was 100 per cent effective in a wheat-on-wheat system, but there were resistant wheat varieties available.
Hartog and Banks have proved low levels of resistance do produce a yield benefit.
Under similar epidemic conditions, sprayed plots of Hartog yielded 57pc higher than the unsprayed control while the sprayed Banks increased yield by 146pc.
Fungicide success will be directly related to application number and timeliness, Mr Platz said, with maximum yield and quality benefits obtained by keeping the upper leaves free from disease during grain fill.
“If conducting one fungicide spray, growers should time the spray to protect the flag and flag-1 growth stages.”
“This usually coincides with 90pc flag leaf emergence but may be delayed if epidemic progress is delayed.”
One application will provide from 21 to 30 days protection, depending on the rate of application.
A single spray can be substituted for spraying at growth stage (GS) 32, with a second at GS39-49.
With timing critical to a fungicide’s effectiveness, Mr Platz recommended rotating to a non-host crop for the best result.
The GRDC www.grdc.com.au/diseaselinks website contains more information for on strategies for managing yellow leaf spot.
• Further information is available from Greg Platz on (07) 4660 3633.
• GRDC Project Code: DAW00206
• This media release and other media products are available via www.grdc.com.au/media
GRDC Project Code