Growers asked to send in samples to tackle bluegreen aphid resistance

Recent research led by Cesar Australia confirmed bluegreen aphid (Acyrthosiphon kondoi) resistance to many of the chemicals routinely used to control outbreaks in pasture seed crops.  These findings are a first for this species.

Earlier this year – in response to growing industry concerns – AgriFutures Australia (AgriFutures), together with Lucerne Australia, invested in preliminary research to investigate potential resistance of bluegreen aphids to commonly used insecticides.

The project revealed that bluegreen aphid populations in key lucerne-growing regions of New South Wales (NSW) and South Australia (SA) were resistant to organophosphates, carbamates and pyrethroids, and recommended a number of important short-term management solutions to minimise crop damage. You can read the full report here.

A subsequent project has commenced building on this preliminary research. It seeks to contribute to the development of long-term pest management guidelines to mitigate the potentially devastating impact of bluegreen aphids, whilst carefully considering other lucerne pests and the broader insect community.

As part of this project, Cesar Australia’s research team is calling on pasture seed growers and agronomists to send in samples of bluegreen aphids for resistance screening.

Samples are being sought from SA where resistant populations are already problematic, as well as from NSW, Victoria (VIC) and Queensland (QLD) to determine the spread of resistant bluegreen aphids.

Project lead, Dr Evatt Chirgwin highlighted that key lucerne-growing regions – in the upper and mid-south-east of South Australia – are currently one of their prime targets for sample collections, even if growers have not yet experienced a chemical control failure.

“We are currently targeting samples from across South Australia and the Riverina area of New South Wales because we suspect resistant populations are floating around undetected in these areas”, said Evatt.

“Even if growers have not experienced control failure in these areas, there is a chance that a resistant population has recently spread to these areas, and we want to know about it”.

Growers and agronomists in other locations in NSW, as well as in VIC and QLD that have experienced control failure are also encouraged to send in samples. Evatt explained that these samples will help map the spread of resistant populations.

“In the preliminary stage of the research, we identified a small number of populations that had evolved insecticide resistance, which was the first case of resistance in this species.

“In this new phase of the research we want to understand where resistance has spread, to which crop type and if the resistance is stable or is increasing over time. A better understanding of these elements will help us to provide regional specific and more sustainable recommendations to growers.”, Evatt said.

Sending in a sample

To send in samples, growers need to use a non-crushable plastic container, a number of leaf samples, a piece of paper towel and an overnight express post bag.

“We’ve created a step-by-step guide which is available on Cesar’s website, but the main thing is collecting at least 50 aphids and any mummified aphids.

“Growers should start by placing a piece of paper towel in the bottom of a firm container. After they have located a population in their crop they should cut leaf samples from the plant directly into the container to ensure the aphids are not disturbed”, Evatt explained.

To guarantee samples are processed in a timely manner, growers are encouraged to send samples by overnight express post on Mondays through to Wednesdays, only. Growers should avoid sending samples towards the end of the week or over the weekend.

Samples can be addressed to:

Bluegreen aphid resistance testing service

Evatt Chirgwin

Cesar Australia

Level 1, 95 Albert St

Brunswick VIC 3056

Once samples have been posted, growers are asked to notify Cesar Australia via email at echirgwin@cesaraustralia.com.

Growers can be reimbursed for the cost of postage by emailing their tax invoice to Cesar Australia.

To read more about sending in your bluegreen aphid samples, visit: https://cesaraustralia.com/resources/sending-aphids-for-resistance-testing/

Short-term management strategies for bluegreen aphids

Growers who think they might be experiencing infestations of resistant bluegreen aphid populations are encouraged to apply the short-term management strategies listed below.

1. Implement chemical rotational strategies and minimising overall chemical use 

Lucerne seed growers should modify their insecticide control strategies for bluegreen aphids by reducing their overall use of organophosphates, carbamates, or pyrethroids, where practical. Continuing the use of these chemicals will favour the resistance in bluegreen aphids.  Where insecticide sprays are necessary to control bluegreen aphids, growers are advised to use MainMan®, which has recently been approved under an emergency permit for bluegreen aphids in lucerne (for seed production only).

2. Monitor for bluegreen aphids

Growers and advisors should closely monitor bluegreen aphid presence and density during times when aphid outbreaks are most likely – late winter and spring. Bluegreen aphids can be monitored using sticky traps to detect aphid flights and direct searches within crops.

To help correctly identify the aphid species, growers should leverage the GRDC crop aphids back pocket guide.

3. Support natural enemies of bluegreen aphids

Supporting natural enemies of bluegreen aphids is critical during the earlier stages of establishing lucerne due to the limited insecticide options available. Hoverflies, lacewings, parasitoid wasps, and ladybird beetles are all known aphid predators and are likely to suppress bluegreen aphids.

Growers are encouraged to carefully select chemicals that are less likely to harm known natural enemies of bluegreen aphids. To do so, growers should leverage the toxicology guide that Cesar Australia has developed for the grains industry.

Although this guide does not provide a comprehensive list of natural enemies and pesticides relevant to lucerne seed growers, the guide does include the susceptibility of several bluegreen aphid natural enemies to many of the active ingredients used on pests in lucerne seed crops. Flonicamid, the active ingredient used in MainMan is found to have a low impact on a several natural enemies of bluegreen aphids.

4. Apply methods to mitigate the damage bluegreen aphids

Bluegreen aphid outbreaks are most common during spring, but growers can apply practices at other times of the year to help prevent outbreaks. Weeds in or nearby crops can provide bluegreen aphids with ‘green bridges’ – alternative plant hosts for pests – when crops get sprayed or resowed.

Growers should monitor and remove weeds known to host bluegreen aphids (e.g. medics) to eliminate these potential refuges for bluegreen aphids prior to sowing new crops.

5. Use bluegreen aphid resistant lucerne cultivars (varieties)

Selecting lucerne cultivars (varieties) with higher resistance to bluegreen aphids can limit damage by producing biochemical compounds that reduce aphid survival and reproduction, reducing the preference of aphids and have a higher damage tolerance.

Guides are available to help growers and advisors select lucerne cultivars based on their bluegreen aphid resistance.