Insect pests harder to control as resistance grows

List of resistant pest insects growing for cropping

Sub clover, while having moderate tolerance to blue green aphid, and only occasionally experiencing major infestations, without appropriate control, often involving a suitable insecticide, can still suffer substantial damage.

Increasingly, like weeds developing resistance to herbicides, insects are also increasingly evolving resistant to many currently used insecticides.

Hence like for weed control, it is important to keep on top of developments in various important insects and their resistance status against any given insecticide. And like for weed control, researchers advise don't depend on any given product, when using insecticides rotate their use with other products, and follow integrated control strategies that include practises such as resistant varieties wherever possible.

Aphid resistance

Blue-green aphid (Acyrthosiphon kondoi) pesticide resistance in, a major pest in lucerne, medics, clovers, and crops like lupins, is an example.

Research undertaken by Dr Evatt Chirgwin and colleagues, and involving AgriFutures Australia, Cesar and Lucerne Australia, has confirmed emerging resistance to commonly used products omethoate, chlorpyrifos and pirimicarb (all with many commercial product names).

Research is also testing for resistance to alpha-cypermethrin.

Also read: Biological insecticide receives registration

Dr Evatt Chirgwin and colleagues have and are testing blue-green aphid populations collected from key lucerne-growing areas in NSW and SA for evolving resistance.

Investigations through collaborative research with CSIRO, suggest these may be the first to evolve resistance to insecticides for this species.

The team is also undertaking preliminary molecular work to determine how this resistance is evolving.

Lucerne, one of the main hosts for blue green aphids. Resistant varieties is an important control strategy.

Blue-green aphids feed directly on the foliage, damaging plants and spreading harmful viruses.

They mainly feed on the upper leaves, stems and terminal buds of host plants.

Blue-green aphids are grey-green to blue-green coloured and can be distinguished from other aphids by their long legs, antennae and cornicles.

They are widely distributed and found in all Australian states.

They are most common in spring but also active in autumn and winter.

Increasing insecticide resistance in blue-green aphid (and as well for other insect pests), means extra consideration is required for what is termed "integrated" pest management.

Proper pest identification and regular monitoring in vulnerable crops and pastures during bud formation to late flowering is needed.

Natural enemies can be very effective at controlling aphid populations.

These include ladybird beetles, parasitoid wasps, hoverflies, and lacewings, all effective at suppressing blue-green aphids.

Naturally occurring aphid fungal diseases (Conidiobolyus obscurus and Pandoraneoaphidis) can also affect aphid populations.

It is also sound practise to reduce aphid damage by selecting varieties that are more resistant to blue-green aphid feeding damage.

Lucerne

For example several lucerne varieties have good tolerance to blue-green aphids.

Many of these varieties also have good resistance to another common lucerne, medic and clover aphid, spotter alfalfa aphid.

Controlling weeds around crops during summer and early autumn to remove alternate blue-green aphid hosts between growing seasons is also sound practice.

Naturalised pastures, such as burr medic, can be badly damaged by blue green aphids. Checking for build-up of natural enemies can provide effective control.

If chemical options are required Dr Evatt Chirgwin advisers avoid spraying with organophosphates & carbamates.

If needed Flonicamid (MainMan) has an emergency permit approved for use on blue-green aphids in lucerne and sulfoxaflor (Transform) is registered for use on in some pulse crops.

Dr Chirgwin and colleagues research is supported by Agrifutures and Lucerne Australia.

He also acknowledges cooperating farmers and advisors who provide samples for resistance testing.

Early insecticide baseline research on aphids, including on blue-green aphid, has been undertaken in conjunction with CSIRO.

GRDC contributed funding for preceding blue-green aphid research in conjunction with CSIRO.

For more information about blue-green aphid control contact Dr Chirgwin echirgwin@cesaraustralia.com

Next week: Be certain of ways to build soil carbon.

  • Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.

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