Are there Russian wheat aphid in your wheat or barley? A short guide to checking and identifying.

Melina Miles   July 27, 2016   Comments Off on Are there Russian wheat aphid in your wheat or barley? A short guide to checking and identifying.

Key points

  1. Conditions suitable for the usual cereal aphid species will also be suitable for RWA. Aphid populations typically build rapidly in late July and August.
  2.  Do not assume aphids in cereals are just the usual oat and corn aphid. In the event of a Russian wheat aphid (RWA) infestation, early detection in spring is critical to prevent yield loss.
  3.  Multiple aphid species may occur in the same crop.
  4.  Familiarise yourself with the symptoms of RWA infection. These may be the first things you notice in a crop.
  5.  Report suspect aphid incidence. contact details provided at the end of the post.

Leaf symptoms caused by RWA feeding
Watch a video on detecting RWA in the field
RWA induce striking symptoms in wheat and barley, unlike the oat and corn aphid which produce no obvious symptoms. RWA do not infest broadleaf crops. Plant damage is in response to direct aphid feeding, so only the infested leaves and/or tillers show symptoms, which usually appear within a week of infestation.

1. White streaking of the leaves. Some varieties show reddening.
Clear_RWA_nymphs_close_IMG_2217 Aphids_white streaking_close_IMG_2140

Reddening_close_IMG_21902. Rolled leaves. RWA colonies shelter inside the rolled leaves.
3 leaves rolled_IMG_2201 RWA_adult_nymphs_unrolled_IMG_2263

 

 

 

 

 

 

3. Infestation up to head emergence can cause rolling of the flag leaf, resulting in the head being trapped in the boot.
flag_curled_IMG_2274

 

 

 

Some of these symptoms are similar to those caused by wheat streak mosaic virus (WSMV) and phenoxy damage in cereals. Close examination of symptomatic plants to determine the presence of RWA is recommended.

Sampling strategy
Single white tiller_IMG_2145Sample tillers and score the presence of aphids. Each tiller is scored as infested (or not), and the level of field infestation is calculated as a percentage of sampled tillers. For example, 100 tillers sampled from across the field; 35 tillers had RWA present; therefore, the field has an infestation rate of 35%. A tiller-based sampling protocol is simpler and more reliable than counting aphid numbers, which can be very variable between tillers and very time consuming to do on whole plants.
Sample tillers randomly from across the field. At low density, there may be just a affected tiller on a plant, and can be difficult to see in a big crop.

It is not known whether RWA infestations will display the edge effect often seen with other aphids (densities are highest around field edges where the aphids have moved in from nearby hosts, or been concentrated by movement on prevailing winds). A random sampling approach provides the best chance of encountering a patchy pest like RWA.

Aphid identification

ID table_beatsheetReporting RWA detections, or suspect populations
If RWA are detected in crops in NSW or Queensland, notify the relevant authority. Until the first confirmed detections in these states, RWA is a notifiable pest. No detections confirmed at 20 July, 2016.

Queensland Reports to Biosecurity Queensland on 13 25 23 or email photos of symptoms/aphids to plantpestdiagnostics@daf.qld.gov.au.

New South Wales Exotic Plant Pest Hotline 1800 084 881 or reports are requested using the online RWA Reporting Tool

National Exotic Plant Pest Hotline 1800 084 881 – calls to the Hotline are transferred to contact points in each jurisdiction

Aphid identification resources:
GRDC Crop Aphid Backpocket Guide
I Spy – Insects of Southern Australian Broadacre Farming Systems Identification Manual (available for download or hardcopy purchase)