Aphid numbers have surged recently
- Bruce Rock
David Stead (Anasazi Agronomy) has reported a sudden increase in cabbage aphid populations in some canola crops at Bruce Rock late last week. He suspects the aphids may have increased dramatically from previous frost events, which have been shown to increase aphid reproduction because of higher nutrient levels available for the aphids in frosted plants. David noted that parasitised aphids (mummies) could be seen when monitoring previously, but the aphid populations had increased to colony sizes on the branches as long as his arm.
Agworld user(s) have reported high cabbage aphid activity in canola crops near Westonia and low turnip aphid activity in canola crops near Bulyee and Corrigin.
A farmer near Wandering recently reported finding cabbage aphids along the edges of a Bonito canola crop. The crop is at the pod ripening stage.
The Curtin University’s Centre for Crop and Disease Management (CCDM) team says that it appears to be be a mixed bag aphid-wise for canola crops in Williams. The CCDM team has reported that its canola trial sites were absent of aphids, but cabbage aphids were found in other canola crops located nearby while the team was travelling in the Williams area.
Growers and consultants are advised to re-check canola crops for aphids, even if they have been previously sprayed, especially if the crop has experienced frost.
The spray threshold of 20% of plants infested with colonies of cabbage or turnip aphids is not applicable at the advanced podding/grain fill stage because the research for thresholds had focused on flowering crops and effects on flower abortion and reduced seed set. Trial work conducted in Queensland on cabbage aphids suggests that infestations after bolting are not yield limiting. For more information refer to the GRDC Update paper Insect Pest Management Research Update 2017.
However, further research is required for these scenarios to adjust the threshold for when spraying is worthwhile at this advanced growth stage. Even so, DPIRD research has shown that pods infested with colonies of cabbage aphids can result in very shriveled seed which would not even be picked up by the header.
Growers are reminded to abide by the withholding periods on the product labels.
For more information on identifying and managing canola aphids refer to the department’s;
- Aphid management in canola crops page
- Diagnosing canola aphids page
- 2017 Protecting WA Crops Issue 3 newsletter Aphids – WA’s insect problem children
- Aphids in your crops YouTube video.
Aoife Goggin (Kalyx) recently found an isolated infestation of oat aphids in a barley crop (variety unknown) near Jennapullin.
Oat aphids are the most abundant species of cereal aphids and vary from mottled yellow-green through olive-green and dusky brown, to a blackish green, and are characterised by a reddish patch on the tip of the abdomen.
Oat aphid colonies develop on the outside of tillers from the base upwards on stems, nodes and backs of mature leaves, starting any time between seedling stage and grain filling.
For more information on cereal aphids refer to the department’s Diagnosing cereal aphids page.
To date, the cereal aphid called Russian wheat aphid (RWA) has not been found in WA, so growers and consultants are reminded to monitor for this pest which, in addition to feeding damage, can inject toxins into cereal plants further stunting them and reducing yields. For more information on RWA refer to the department’s Diagnosing russian wheat aphid and Biosecurity alert - Russian wheat aphid page.
For a list of insecticides registered for use on aphids see the department’s 2018 Winter/Spring Insecticide Guide.
For more aphid information contact Dustin Severtson, Development Officer, Northam on +61 (0)8 9690 2160 or Alan Lord, Technical Officer, South Perth on +61 (0)8 9368 3758 or Svetlana Micic, Research Officer, Albany on +61 (0)8 9892 8591.