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Green peach aphid quiet but not controlled

While populations of green peach aphid have been reported recently, their activity and the risk of virus transmission has decreased with the onset of winter… 

Where have they been reported?

Green peach aphids (Myzus persicae, GPA) have been reported in canola in high numbers near Kaniva in the Victorian Wimmera. Prior to receiving a knockdown spray, the paddock hosted broadleaf weeds, which may have served as a host to the pest prior to the cropping season. Imidacloprid seed dressing was not effective in controlling this population, which could indicate the development of resistance to neonicotinoids. Pre-sowing and post-emergent applications of organophosphate and synthetic pyrethroid insecticides, respectively, also failed to provide adequate control.

Reports we have received suggest numbers of GPA are low compared with the same time last year. For instance, low populations (5 – 10/m2) have been reported in canola near Deniliquin in the NSW Riverina, where omethoate failed to provide adequate control.

About GPA

GPA grow up to 3 mm long and vary in colour from shiny pale yellow-green, green, orange or pink.  The colour variants bare no relationship to the aphids’ susceptibility to insecticides. Nymphs are similar to wingless adults but smaller in size. 

GPA are not always green (left); they are often orange-pink in colour (right) (Source: cesar)

 

GPA has a very wide host range, including oilseeds, lupins, pulse crops, broad leaf weeds and some broad leaf pastures. They are common in many horticultural crops including crucifer vegetables. Non-crop hosts include capeweed, marshmallow, wild radish, wild turnip, Lincoln weed and other cruciferous weeds. Weeds and volunteer crop plants growing in summer and autumn provide a ‘green bridge’ for aphid populations to survive between cropping seasons. GPA is often misidentified as turnip aphid (Lipaphis pseudobrassicae) or cabbage aphid (Brevicoryne brassicae), which attack similar hosts.

GPA are often confused with turnip aphid (left) and cabbage aphid (right) (Source: cesar)

 

Under certain conditions, GPA are an important vector of plant viruses including turnip yellows virus (TuYV)(syn. beet western yellows virus), cauliflower mosaic virus (CaMV), turnip mosaic virus (TuMV) and cucumber mosaic virus (CMV), all of which damage canola. This year, TuYV has been identified in canola in a number of regions of SA in very early sown crops, and in spring-sown grazing canola in southwestern Victoria.

Our advice

GPA numbers are now likely to decline due to the increasingly cold and wet conditions in most regions. Insecticides should only be applied when absolutely necessary.

There are several insecticides registered against GPA. However, many populations have developed resistance to a range of chemical groups. In Australia, GPA are resistant to synthetic pyrethroids, carbamates (e.g. pirimicarb) and organophosphates. Recent research by cesar and CSIRO has also identified low levels of resistance to neonicotinoids (e.g. imidacloprid) in some populations.

To reduce the risk of insecticide resistance, rotate insecticides from different chemical groups, avoid the use of broad-spectrum insecticides, and apply appropriate insecticides only after careful monitoring and correct identification of species. Growers and advisors are encouraged to download, and follow, the GPA Resistance Management Strategy to minimise the further development of resistance.

Click here fore more information on GPA.

Have you spotted GPA?

We are currently seeking samples of GPA from NSW for insecticide resistance testing against four major chemical groups. We are specifically looking for populations in canola crops. To send us a sample, please follow these instructions. For further information contact Dr Siobhan de Little on (03) 9349 4723 or via email at sdelittle@cesaraustralia.com.    

 

Sources of field reports of green peach aphid

Frank Henry – Regional Research Agronomist (South West Victoria)

Simon Mock – Agronomist, Clovercrest Consulting (Victorian Wimmera)

John Stuchbery – Agronomist, AGRIvision Consultants (Victorian Wimmera)

 

Twitter sources:

Connor Byrne (@cobyrne_)

Adam Dellwo (@AdamDellwo)

 

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