Australia
December 16, 2015

Sorghum midge could be a huge problem for growers in the northern region this season, given record sorghum plantings and a mostly warm and humid start to summer cropping.

The Grains Research and Development Corporation (GRDC) estimates costs from residual losses and uncontrolled sorghum midge could reach up to $10 million annually.

Principal Entomologist with the Queensland Department of Agriculture and Fisheries (DAF) Dr Melina Miles said growers using an integrated pest management strategy to control sorghum midge could avoid major damage and repeat insecticide applications over the season.

“By strategically using midge-tolerant hybrids, particularly for those considering later season plantings around Christmas/January, the industry can significantly reduce this difficult pest situation,” she said.

“The Grains Research and Development Corporation, in partnership with DAF and breeding companies, have a protocol for measuring midge resistance levels in grain sorghum hybrids which assigns official ratings to commercially released lines.

“The number is a measure of the amount of grain lost per visiting female midge per day and ranges from 1, meaning no resistance to 8+, being practical field immunity.

“All new hybrids are subject to this protocol to ensure growers can make an informed decision each planting.

“It’s also important growers manage the non-crop hosts of the pest such as Johnson grass, often found on roadsides or along irrigation channels.

“Sorghum midge will have established in any Johnson Grass over the spring, particularly given the warm and damp conditions in many areas.”

Dr Miles said peak midge activity generally occurs between 9-11am, so this was an ideal time for growers to check.

“They will normally be seen in sorghum heads at mid flower and are only 1-2mm long.”

She said the easiest way to spot these tiny pests was to look at the top half of mid flowering panicles.

“You are looking for the movement of the small red flies against the still sorghum panicle. By focusing your eyes over a couple of floret branches for a couple of seconds at a time, you should be able to detect female midges walking around or probing florets,” she said.

“You can do this over 10 metres of row in at least 4 separate spots in the crop and if you identify midge, I would advise using DAAF’s Economic Threshold Calculator to assess whether you will benefit from applying an insecticide.”

The calculator considers the hybrid’s level of resistance, commodity prices, insecticide cost and growing conditions.

“One well-timed insecticide for midge, on panicle emergence before the midge enter the crop, will still only prevent 70 – 80% of damage in a lower rate sorghum hybrid, but our data shows in 8 rated hybrids, yield losses can be reduced by over 90%,” Dr Miles said.

To learn more about midge resistance ratings, go to http://bit.ly/1OvwdFq and to use the Economic Threshold Calculator go to http://bit.ly/1Ttfs1X.

Photo by Ken Laws

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

Published: December 16, 2015