Grains Research and Development

Date: 04.03.2013

Check sorghum spray out timing

GRDC-funded results in a nutshell

Grain yield: spray out

  • three weeks early resulted in greater than 50 per cent yield loss;
  • two weeks early resulted in greater than 20 per cent yield loss; and
  • one week early resulted in an average 10 per cent yield reduction.

Grain quality:

  • impact on grain quality was also significant but less affected than yield; and
  • actual screening levels were increased by  about five per cent when timing was two weeks early, with negligible impact when one week early.

Soil water impact:  

  • at appropriate spray out timings, soil water conservation at depth (below 30 centimetres) ranged from 0 to 24 millimetres with average levels of less than 10mm; and
  • this soil water at depth can have significant benefits for the next crop in the rotation as it is likely to be used with greater efficiency.

Tools for application timing:

  • grain or head moisture is impractical;
  • about 35 days after flowering is a useful guide to determine when you should start to inspect individual paddocks; and
  • assess black layer on heads of the latest maturity you want to harvest. Time spray-out on these heads.


Pre-harvest lodging remains a risk for sorghum growers as crops may be carrying the Fusarium pathogen after recent rains.

James Clark, GRDC northern panel chair, says GRDC-supported research shows spray out in stressed crops can cause pathogens to spread rapidly throughout the sorghum plant, causing lodging and yield loss. 

“The message for growers is not to get too far ahead of the header with the spray out program, particularly when there is a risk of rain,” Mr Clark says.

“Sorghum crops shouldn’t be left standing in paddocks for weeks before harvest.”

Northern Grower Alliance (NGA) and New South Wales Department of Primary Industries (DPI) research shows desiccation or spray out using glyphosate when grain moisture is more than 25 per cent reduces grain yield and quality and increases the risk of lodging when harvest is delayed.

Dr Guy McMullen, NSW DPI research leader for northern farming systems at Tamworth Agricultural Institute, says timing is crucial to avoiding yield loss.

Dr McMullen says desiccating too late carries the risk of poor returns on the spray operation and may result in lost soil moisture and the consequent impact on future planting options.

“Sorghum growers and advisers in Queensland seem more comfortable with optimal timing of sorghum spray out, largely based on grain black layer (abscission zone) development,” Dr McMullen says.

“However industry feedback in northern NSW indicates growers and advisers are frequently much more conservative in their spray-out timing.”

He says results from the NGA research are clear – growers should identify heads of the latest maturity considered ‘economic to take to harvest’.

Second, ensure the black layer formation has occurred in the bottom third of these heads prior to spraying out, he says.

More information:

www.grdc.com.au/diseaselinks

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GRDC Project Code NGA00002

Region North, South