Images left to right: 1. Russian wheat aphid on wheat near Cressy. 2. Russian wheat aphid feeding symptoms on wheat near Cressy. 3. Feeding symptoms on barley near Launceston. Photos: Guy Westmore, Biosecurity Tasmania
Detection of a New Pest in Tasmania
Russian wheat aphid, a new pest of wheat and barley was first detected in Australia, at Tarlee in South Australia, in May 2016. A national management committee determined it was beyond eradication and expected to spread rapidly. By October 2016 it occurred across much of the wheat and barley belt of South Australia, Victoria and southern New South Wales.
Russian wheat aphid was first detected in Tasmania at Cressy in January 2017. It is likely to have arrived naturally on northerly airflows. As of January 2021 it has been recorded at several locations in the Northern and Southern Midlands and also near Devonport, Deloraine and Westbury and is likely to be widespread across these areas.
History
Russian wheat aphid is indigenous to central Asia and southern Russia. It was considered a minor pest until it appeared in South Africa in 1978 where it became a major pest of wheat. In the last 30 years it has spread to other parts of the world, including North and South America. Australia was one of the last major grain producing countries to remain free of the pest.
Impact
Russian wheat aphid,
Diuraphis noxia, is a small green aphid whose feeding produces strong plant symptoms due to the injection of saliva into the plant. Symptoms include rolled leaves, chlorotic spots, prominent leaf streaking, trapped awns giving a hooked appearance, and a stunted crop. Russian wheat aphid can cause direct yield losses and damage, unlike other aphids which are a problem because they transmit viruses.
The presence of the aphid is unlikely to seriously impede market access for Australian exports of grain but feeding by the aphid will reduce yields and may increase crop management costs.
Russian wheat aphid is best adapted to the dry climate of the mainland Australian wheat belt and not well adapted to the moist Tasmanian climate. Its impact in Tasmania, although undesirable, is anticipated to be less than in the dry wheat belt areas of the mainland. However, the lack of a gap between summer and spring cereal crops in Tasmania may foster the pest.
Russian wheat aphids spend their entire life on cereals and grasses. They survive only a few days without feeding on suitable plants. The hosts that are most severely affected are barley (Hordeum vulgare) and wheat (Triticum
aestivum). Other primary hosts include durum wheat (Triticum durum), field broom grass (Bromus arvensis), Elymus sp. and jointed goatgrass (Triticum cylindricum).
Secondary hosts are plants that only support adults and older juveniles. They allow the aphid to survive but not reproduce. Secondary hosts include cereal rye (Secale cereale), triticale (Triticum aestivum x Secale cereale) and various grasses in the
Poaceae family, such as oats (Avena satvia), tall wheat grass (Agropyron elongatum) and Indian rice grass (Oryzopsis hymenoides).
Russian Wheat Aphid is not moved via harvested cereal grain. It does however disperse widely on the wind.
Identification and Reporting
Reporting of suspect occurrences of Russian wheat aphid is encouraged to help map the distribution of the pest. The Entomology Team in Plant Diagnostic Services of NRE Tas will identify aphids suspected of being Russian wheat aphid at no fee. For an initial opinion, clear photos (with location) can be sent to 0429 852 886 or emailed to
Guy.Westmore@nre.tas.gov.au. Specimens may be requested before making a final identification.
Specimens can be submitted to Plant Diagnostic Services at Mt Pleasant (Launceston), Stony Rise (Devonport) or New Town (Hobart) in person or by post. Samples of plants bearing aphids should be secured in sealed double plastic bags along with some absorbent paper towel.
Alternatively, contact
1800 084 881 to report a suspect occurrence of this aphid and direction to an entomologist in Plant Diagnostic Services.
Management Advice
If you face a heavy infestation, seek advice from a commercial agronomist.
In many cases growers will not need to spray to control Russian wheat aphid. Sprays are not preventative. Spraying low populations of Russian wheat aphid or other pests will kill predators and other beneficial insects, potentially causing resurgence to higher levels of Russian wheat aphid and other pests later in the life of a crop. If spraying is warranted, aim to use softer chemistry to encourage natural predators and beneficial insects.
Consider the economics of control. International advice supports an economic threshold of 20% of plants infested up to the start of tillering and 10% of plants infested thereafter. This may change once infromation from Australian trials is completed.
More information on management of Russian wheat aphid, including the GRDC FITE Strategy, can be found at Plant Health Australia.
Identification of Russian wheat aphid
Monitor crops for signs of Russian wheat aphid.
Learn to recognize the symptoms in wheat and barley plants., which can resemble herbicide damage. Symptoms include rolled leaves, chlorotic spots, prominent leaf streaking, trapped awns giving a hooked appearance and a stunted crop.
The aphid itself has diagnostic features as in this image:
Image: Key identifying features of Russian wheat aphid (D. noxia). Photo: Nicholas A. 2011 (Oklahoma)