Cereal aphid update
Oat aphids
- Northamptom
- Shackleton
- Kumminin
- Yerecoin
- Beverley
- Katanning
- Gairdner
The PestFax team has received numerous reports of oat aphid activity recently.
Oat aphids have been found by Belinda Eastough who recently tweeted that cereal aphids in Devil wheat at Northamptom were starting to exceed spray thresholds.
David Stead (Anasazi Agronomy) reports that oat aphid numbers have ‘exploded’ in barley at Shackleton to south of Kumminin and Beverley to Yerecoin. Oat aphids are also in wheat crops at Yerecoin.
Below threshold numbers of oat aphids have also been found in wheat at Katanning and Gairdner.
Russian wheat aphids
- Newdegate
- Lake King
- Gairdner
- Gibson
Nathan Moyes (Moyes Agri Consulting) has reported finding Russian wheat aphid (RWA) in Planet barley crops at Newdegate, Lake King and Gairdner. These crops did not have a seed dressing treatment.
An Agworld user has recently reported finding RWA in a wheat crop near Gibson.
Managing cereal aphids later in the season
Direct feeding damage from aphids occurs when colonies of aphids develop on stems, leaves and heads, usually in the tillering and later stages of crop growth through to head filling. The degree of damage depends particularly on the percentage of tillers infested, the number of aphids per tiller and the duration of the infestation. If low numbers of aphids are observed, wait until threshold levels are reached before considering control options.
RWA thresholds are dependent on the crop stage, the time until head emergence, predicted yield and cost of spraying. A RWA threshold calculator is available on GRDC’s Russian wheat aphid page.
Barley crops are most at risk from corn and oat aphids due to the possibility of downgrading from malt to feed quality, as aphid feeding damage can cause grain shrivelling. If 50% of tillers have 15 or more aphids then the feeding damage may cause reductions in yields by up to 10% and also reduce grain size. Yield loss is greater in crops that had aphid colonisation from early tillering.
Aphid colonisation of cereal crops at the flowering stage does not lead to yield loss.
Remember that naturally occurring parasitoids and predators such as hoverflies, wasps, lacewings and ladybird beetles will also increase with warming weather. These predators can keep aphid populations below threshold levels and un-necessary spraying of “anti-feed” synthetic pyrethroid sprays will only counteract their benefits. When spraying, consider spray options that are soft (for example pirimicarb) on predators. Hoverflies have been reported this week, refer to DPIRD’s 2021 PestFax Issue 16 article Beneficial hoverfly larvae.
Also dense aphid colonies are prone to fungal pathogens. Aphids infected by fungi are sluggish and have white to yellow ‘fur’ covering their bodies. The fungus can readily spread throughout aphid colonies. The fungus can be more effective in decreasing aphid populations than chemical control.
For a list of insecticides registered for use on aphids (including RWA) see DPIRD’s 2021 winter spring insecticide guide or refer to the Australian Pesticides and Veterinary Medicines Authority (APVMA) products database for all chemical control options available for RWA in grains crops.
For more information on cereal aphids, and previous activity this season, refer to DPIRD’s:
- Diagnosing cereal aphids page.
- DPIRD’s Diagnosing Russian wheat aphid page.
- 2021 PestFax Issue 10 article Russian wheat aphid update
- 2021 PestFax Issue 8 article A variety of cereal aphids are active
- 2017 Protecting WA Crops Issue 3 newsletter Aphids – WA’s insect problem children.
For more information on aphids contact Svetlana Micic, Research scientist, Albany on +61 (0)8 9892 8591 or Alan Lord, Technical officer, South Perth on +61 (0)8 9368 3758.
Article authors: Cindy Webster (DPIRD Narrogin) and Svetlana Micic (DPIRD Albany).