Pest Alert: Russian Wheat Aphid
- Russian Wheat Aphid is a common pest of grain crops around the world
- Weekly scouting and timely insecticide applications can help protect grain yields
- Controlling volunteer grasses and adjusting planting dates can help reduce outbreaks
- Talk to your Elders agronomist if you have any questions
Russian Wheat Aphid (RWA) is a common pest of wheat, barley and other cereal grains in cereal production regions with warmer, drier climates around the world. RWA had not previously been reported in Australia however its presence has recently been confirmed in cereal crops in the mid-North of South Australia. While the introduction of any exotic pest into Australia is regrettable, it is important that the discovery of RWA does not lead to over-reactions and poor decision making. RWA can cause significant crop damage and yield losses, however it is a pest that has been effectively managed in many grain growing regions of the world.
What is Russian Wheat Aphid?
RWA is an aphid that can cause significant damage and yield losses, particularly in infected wheat and barley crops but also in triticale and oats. While the damage caused by other aphid species is limited to the removal of nutrients or introduction of other path-ogens (viruses), RWA injects toxins into the plant while feeding that can have a significant impact on plant growth.
The host range of RWA includes wheat, barley, tritica-le, rye, oats and the majority of grasses found in temperate Australia. These include pasture grasses and wild grasses such as winter grass (Poa), barley grass, brome grass, ryegrass and phalaris species.
RWA is relatively easy to identify by both it’s appearance and the damage it causes to crops. The aphids secrete a toxin that causes leaf rolling and white (warm weather) or purple to red (cool weather) streaking on the leaves. Damage appears first as patches of stunted or discoloured plants which resemble drought-stressed areas.
Heavily infested plants are often stunted and may ap-pear flattened, with tillers lying almost parallel to the ground. From a distance the damage may appear as a general loss of colouration across the affected crop area. Later in the crop cycle, wheat awns can become trapped by rolled leaves, resulting in hook-shaped head growth, bleaching and reduced yield.
The aphid is small (up to 2mm long) and can be either wingless or winged. The wingless aphids are light green with an elongated and spindle-shaped body with short antennae. It has a projection (cauda) above the tail that gives it a two-tailed appearance and lacks visible siphuncles (‘exhaust pipes’) that are a charac-teristic of most aphids. The winged aphids, usually present later in the crop cycle as populations build, are generally darker green and have longer, body length, antennae.
Colonies are found most often in tightly rolled leaves near the base of the leaf, in leaf whorls, or concealed on the stem inside the flag leaf sheath. Aphids prefer the newest leaves of plants, and are often found on the last two leaves unfurled. At high densities they can be found on any foliar parts and may be more broadly distributed over plants during fine weather.
Note: Any suspect aphids or unusual damage should be reported to the Exotic Plant Pest Hotline on 1800 084 881.
Crops should be checked regularly for the presence of new or unusual pests and plant damage symptoms. Aphids may infest crops during any stage of crop de-velopment, from early establishment to maturating flag leaf. Check crops regularly following seedling emergence for the characteristic leaf streaking and rolling.
Infestations often begin along crop edges, usually on the windward side or adjacent to infested grasses. RWA also commonly occurs in areas of paddocks where plants are sparse or adjacent to bare ground. After initial infestation, aphids can rapidly spread across a paddock.
Chemical control of RWA can be effective although due to the aphids often inhabiting the base of the plants, inside rolled leaves, high water volumes (100-120 L/ha) are required to maximize coverage. In many regions, organophosphate insecticides are commonly recommended and seed treatments may offer some early season protection.
Decisions on the need for foliar treatments are based on the proportion of seedlings or tillers infested. While threshold guidelines (ET) are still being defined for Australia, current recommendations for early sea-son growth is an ET of 20% seedlings infested up to the start of tillering, and 10% seedling infested there-after.
An APVMA permit (PER81133) has been issued for the use of products containing chlorpyrifos or pirimicarb. For more information regarding chemical control op-tions talk to your Elders agronomist.
Cultural controls include eliminating refuge volunteer cereals and grasses in fallows and other areas during summer and autumn; later planting of winter cereals to delay and reduce early aphid infestation; agro-nomic practices to promote crop vigour and dense canopy growth, which inhibit RWA populations and reduces their impact on the crop. Wheat cultivars with resistance to RWA are also used in some countries.
Like most aphids, populations of RWA are strongly regulated by environmental conditions. Survival of aphids outside the shelter of leaf rolls is affected by exposure to rainfall, drying winds, predators and para-sitoids. Rainfall washes aphids from upper leaves, and heavy rainfall may cause 50% mortality. Populations are generally reduced by cold and wet conditions.
Adopt best-practice farm hygiene procedures to reduce the spread of the pest between fields and to adjacent properties.
- Keep traffic out of affected areas and minimise movement in adjacent areas.
- To disinfect footwear, mix a 1% active chlorine solu-tion in a container and soak boots for at least 30 sec-onds after removing excess mud and dirt. Use gloves and avoid splashing the solution onto exposed skin or clothing.
- Wherever possible, put on disposable overalls before entering an infected or suspect paddock and if RWA is suspected, remove overalls before getting back into the car and place in a sealed bag for incineration.Acknowledgement
The information in this factsheet has been adapted from Primary Industries and Regions SA (PIRSA), Plant Health Australia, Oregon State University and the University of California websites and factsheets.
Primary Industries and Regions SA www.pir.sa.gov.au
Plant Health Australia www.planthealthaustralia.com.au
Oregon State University www.extension.oregonstate.edu
University of California www.ipm.ucdavis.edu
For further information regarding Russian Wheat Aphid identification and management or other agronomic advice, please contact your local Elders agronomist.