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Russian wheat aphid update

As further populations of Russian wheat aphids are detected in Victoria, a national technical group under Plant Health Australia has agreed on some current management recommendations… 

Where have they been reported?

Since its initial detection in Victoria, further detections of Russian wheat aphid (Diuraphis noxia, RWA) have been made in the Victorian Wimmera, Mallee and Northern Country districts. We have also received several unconfirmed reports that indicate the distribution of RWA may be wider than this.

Click here to see a current map of the confirmed distribution of RWA in Australia. Plant Health Australia (PHA) will regularly update this data and generate maps that will be viewable via their website. It is expected that aphids will spread to other regions. To date, there have been no confirmed detections of RWA in New South Wales.

A ‘refresher’ on RWA

Wingless adults grow up to about 2 mm long and have distinctively short antennae. They are light green in colour and can appear coated with a whitish wax. In addition, there are three other conspicuous features that can help distinguish RWA from other cereal aphids.

• The first is its elongated body. While the bodies of established cereal aphids are often pear or globe-shaped, RWA is longer and more spindle-shaped.

• The second feature is the apparent lack of siphuncles, which are commonly referred to as ‘exhaust pipes’. These structures are notable on most aphids, however they are very difficult to see on RWA with the naked eye.

• The third diagnostic feature is the presence of two caudae or a ‘double tail’ at the rear end of the aphid. This can be seen best when viewing the aphid from a profile perspective.

 

Russian wheat aphid is light green, elongated and has short antennae (Source: cesar)

 

Wheat, barley and durum wheat are primary hosts to RWA. This means that the pest can feed on these plants at any stage of its lifecycle and reproduction can occur in crop. Other important agricultural crops such as oats, triticale and rice are secondary hosts. These crops only support RWA as an adult and just prior to reaching maturity, meaning that it cannot complete its lifecycle on these crops. There are also many grasses, both cultivated and wild species, which can host RWA. Bromus grasses are particularly important to RWA survival and population build-up.

The RWA is distinct from other cereal pests as it injects salivary toxins in addition to removing nutrients during feeding. Even a few aphids can cause plant damage symptoms to appear as early as 7 days after infestation. These include:

- Curled, rolled or hollow tube leaves

- Discoloured leaves

- White and purple streaks on leaves

- Stunted growth or flattened appearance

- Hooked-shaped head growth from awns trapped in curling flag leaf

- Bleached heads

For further information on RWA see PestFacts Issue No. 3, 2016.

Our advice

A national technical working group on RWA, under the auspices of PHA has agreed on the below current management recommendations:

Monitoring: Crops should be monitored for both RWA and their symptoms. Do not spray in hope of preventing an incursion. Sprays are not preventative and will kill predators and other beneficials, which may exacerbate aphid infestations in spring. It is not known how RWA will behave in Australia, however it is very likely that activity will decline with cooler winter temperatures.

Reporting: If a RWA infestation is suspected, report it to the Exotic Plant Pest Hotline (1800 084 881). It may be necessary to send in a sample for formal identification.

In NSW:

• The NSW DPI situation report and advice on RWA, including details on collecting samples and crop hygiene, is available here.

• Suspect aphids/symptoms must be reported by calling the Exotic Plant Pest Hotline 1800 084 881, or email biosecurity@dpi.nsw.gov.au. This will allow NSW DPI to co-ordinate sampling and identification at the nearest diagnostic lab.

• Negative surveillance reports of where people have looked but not seen RWA or symptoms are also strongly requested. An online RWA Reporting Tool has been developed to support reporting. This information will help to understand the likely distribution of RWA should it be found in NSW this season.

In Victoria:

• The Agriculture Victoria situation report and advice on RWA is available here.

• Victorian samples should be sent to the CropSafe diagnostic laboratory, DEDJTR (Agriculture Victoria), at the Grains Innovation Park, 110 Natimuk Road Horsham for official confirmation.

Economic Thresholds: If RWA is identified, in most cases growers do not need to spray. For the time being, growers are encouraged to adopt international economic thresholds of 20% of plants infested up to the start of tillering and 10% of plants infested thereafter. Please note that these thresholds are situation dependent and trial work is needed to validate them locally.

Control: The GRDC FITE strategy is recommended:

• Find (look for aphids and the characteristic plant symptoms of leaf streaking or leaf rolling on cereal crops and grasses)

• Identify (positively identify RWA in consultation with a specialist)

• Threshold approach (consider international thresholds for control, factoring crop growth stage and potential yield losses)

• Enact an appropriate management strategy that where possible encourages beneficial insects.

Chlorpyrifos and pirimicarb are currently listed for control under Emergency Use Permit (APVMA82792). If spraying is warranted, aim to use the softer chemistry to maintain predators and beneficial populations. Be aware of how spraying can impact in foraging bees – contact beekeepers and see the BeeAware website: beeaware.org.au.

This advice has been developed by the National RWA technical group established by Plant Health Australia (PHA), comprising of representatives from state agricultural departments, cesar, CSIRO, GRDC and PHA.

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