PestFacts Issue 5, 2016 - Russian wheat aphid update
The National Management Group (NMG), comprising all Australian governments, Grain Producers Australia and Plant Health Australia, has agreed (8 June 2016) that it is not technically feasible to eradicate Russian wheat aphid (RWA), Diuraphis noxia, from Australia (see DAWR communique - Russian wheat aphid). Development of a national management plan to help manage the pest in Australia has been initiated by Plant Health Australia. The plan will include a range of elements such as immediate control options, training to promote early detection and best practice management, as well as research and development to provide longer term control options. There are no expected trade restrictions for the export of grain or other commodities to overseas markets.
This decision means that the focus of RWA management should now shift away from local eradication to normal crop protection as for other endemic pests.
For growers, this means use of economic threshold-based decision making, and adjustments to recommendations on insecticide selection and rates (see 'management' section below).
Known distribution and population levels
Further recent confirmed detections have expanded the known distribution of RWA in southern Australia to include the South Australian regions of the Mid North, from the top of Yorke Peninsula to the Clare Valley, through the Lower North, Barossa Valley and Adelaide Hills, Fleurieu Peninsula and SA Mallee. A further affected area has been identified west of Bordertown in the South East, and suspected to be present in parts of Western Victoria (see the latest map of the affected area ).
In most cases, RWA population densities being detected in cereal crops are well-below our current recommended economic thresholds (see 'management' section below). With recent cold and wet conditions, populations of RWA and other aphids appear to have declined. With these conditions expected to continue to reduce aphid activity during winter, in many cases crops infested with RWA will not require treatment at this stage. Overseas observations suggest that heavy rainfall can reduce populations by half. Encouragingly, SARDI entomologists have observed evidence of biological control of RWA, including parasitism and attack by ladybird beetles and fungal pathogens.
Alterations to management approach
With the move from eradication to a long-term management approach for RWA, growers and advisors will now need to adjust their management approach. Normal crop protection applies.
Chemical control - updated recommendations
An APVMA permit has been approved for the use of products containing 500g/L chlorpyrifos or 250 g/kg pirimicarb. For chlorpyrifos, the permit allows for high rates of up to 1.2L/ha (requested for the initial emergency response); however, where treatment is now required, we are recommending a lower rate of 600mL/ha where chlorpyrifos is used. SARDI are currently trialing a range of aphicides registered for aphid control in Australian cereal crops, including dimethoate, omethoate and sulfoxaflor, for efficacy against RWA, with a view to refining recommendations. Recent assessment of a trial of early-sown wheat varieties (sown first week of April) has shown that imidacloprid (600g/L) seed dressing at 240 ml/100kg suppressed RWA for at least 6 weeks.
As for all pests, we recommend crops are treated for RWA only where necessary - i.e. where pest levels exceed economically damaging levels. Based on overseas guidelines for early crop growth, we currently recommend economic threshold (ET) guidelines of 20% seedlings infested up to the start of tillering, and 10% of seedlings infested thereafter. Note that these guidelines are yet to be tested in Australian conditions; ET information will be updated as required in future issues.
We do not recommend the prophylactic use of insecticides in an attempt to control or prevent crop infestation by RWA or other pests. Broad spectrum insecticides are highly disruptive to beneficial invertebrates and can lead to secondary flare-ups of aphids and other pests later in the season. Overseas experience has indicated that natural enemies can play a major role in the natural suppression of RWA populations. Prophylactic spraying also increases the risk of insecticide resistance development, including in non-target species.
We caution against over-use of sulfoxaflor (Transform™) to control RWA in cereal crops; this product is currently the only effective insecticide available to control green peach aphid (GPA) in Australian canola, due to resistance of Australian GPA populations to other major chemical classes. Note that GPA feeding on broadleaf weeds interspersed within cereal crops will be exposed to any insecticide treatments applied.
SARDI entomologists are presenting at meetings for growers and advisers to discuss RWA biology and management. Details of upcoming meetings:
- Karoonda - Tuesday 14 June 2016, 2-4pm, Karoonda Football Club Rooms
- Roseworthy - Crop Science Society Meeting, 15 June 2016, 7:30 pm, Roseworthy Campus
- Keith - Thursday 16 June, 2-4pm, Keith Institute
Collecting aphid samples for identification
To submit samples, collect RWA from infested plants and place them in a vial with 80% alcohol. Methylated spirits can be used. Pack the vial in a non-crushable container or padded postal bag pack and send to:
PestFacts, SARDI Entomology Unit
GPO Box 397
Adelaide SA 5001
Please include all relevant information with every sample submitted.
Ensure all details of host crop, GPS and location description, and collection date are recorded, along with the collectors, and if possible the growers, names.