Green peach aphids

The reported incidences of green peach aphid have grown appreciably across NSW, western Victoria (and also South Australia). They are mostly a concern in early establishing canola because of the risk of virus transmission and feeding damage. Pressures will lessen with wetter and cooler conditions.

Where have they been reported?

The green peach aphid (GPA), Myzus persicae, commonly in association with smaller numbers of the turnip aphid (Lipaphis erysimi), has been widely reported on canola in NSW, the Victorian Mallee and Wimmera, and in South Australia. In a canola paddock northeast of Deniliquin in NSW’s Riverina, GPA have been found in relatively high numbers (50-100 aphids/plant) mostly on the underside of leaves and in the crown of smaller plants. In other areas of Deniliquin, GPA has been found in high numbers on canola, faba beans and lupins, potentially causing some crop delay. Unusually high numbers of aphids have also been observed on forage brassicas around Armidale, Guyra and Uralla in NSW’s Northern Tablelands.

In the Victorian Mallee, GPA have been found in canola crops near Robinvale since early May. Aphid numbers have been quite high on many plants, particularly closer to roadsides. In one paddock, the canola crop was sown with imidacloprid treated seed, which should offer aphid control. In a crop closer to Manangatang, lower numbers of GPA were found on a canola crop and also found surviving imidacloprid treated seed. In the Nhill area of Victoria’s Wimmera, GPA have been reported attacking a canola crop in densities of up to 10 aphids per plant. Infested leaves were distinctively cupping, and the leaf margins and veins turning purple. With limited upper soil moisture, the plants were also beginning to look stressed. In the absence of a formal diagnosis, DAFWA pathologist, Dr Doug Sawkins, acknowledges that these symptoms might be that of turnip yellow mosaic virus (TYMoV), although other causes are possible. Other crops in the district were showing similar signs. The SARDI PestFacts team also report widespread reports of GPA in South Australia.

Green peach aphid habits and behaviour

GPA is a serious pest of canola, some pulse crops and several horticultural brassicas. In grain crops, infestations typically start in autumn when winged aphids fly into the crop from broadleaf weeds and volunteers. Above-average rainfall in March and April provide ideal conditions for aphids to arrive in large numbers early in the season. Cold and wet conditions during winter will suppress population development.

GPA feed by sucking sap from leaves and flower buds, primarily from the underside of plant leaves. When populations are large, the entire crop foliage may be covered, resulting in retarded growth of plants. Young vegetative canola is most susceptible to damage. GPA is rarely of economic importance once canola reaches the 8-leaf growth stage as the natural chemical defences within the plant (particularly glucosinolates) limit their development. Like other aphids, GPA secretes honeydew that can result in secondary fungal infection (for example, sooty mould), inhibit photosynthesis and reduce plant growth and vigour. GPA can transmit more than 100 plant viruses.

Our advice

The relatively mild temperatures of May have provided excellent conditions for GPA spread and build-up. However, as temperatures are now beginning to decline, population growth will slow. Growers should keep an eye out for aphids, as well as the beneficial insects that assist in keeping pest populations in check.

If chemical control is required, be aware of the species present and keep in mind that GPA populations have widespread resistance to several insecticides, including synthetic pyrethroids, organophosphates and carbamates (e.g. pirimicarb). It is important to rotate insecticide classes to help prevent resistance from developing further. Growers are encouraged to keep an eye out for any control difficulties that arise when applying chemicals as per label instructions. We are currently offering a free service to test for resistance in GPA through a GRDC-funded research project. Contact us directly if you would like further details. Click here for further information about resistance management for GPA.

Control options

There is some uncertainty around the economic benefit of controlling GPA at this time of year, particularly once seedlings are well-established and the initial risk of virus ‘spill-over’ has largely passed.

Beneficial insect numbers should be considered before deciding to spray for aphids. They provide a reliable form of biological control and can often keep moderate aphid populations below damaging levels. Aphid natural enemies include parasitic wasps, ladybird beetles, hoverflies and lacewings. The presence of bloated, bronzed coloured aphid ‘mummies’ indicates parasitic wasp activity. Female wasps lay their eggs into the bodies of live aphids. The developing wasp larva feeds inside the aphid, eventually killing it. We have identified several beneficial insects attacking GPA in recent weeks. Click here for more information on identification and management of canola aphids.

Industry recommendations suggest chemical control should be considered if more than 20% of canola plants are infested. When determining economic thresholds it is critical to consider several factors before making a decision. Most importantly, the current growing conditions and moisture availability should be assessed. Crops that are not moisture stressed have a greater ability to compensate for aphid damage and will generally be able to tolerate far higher infestations than moisture stressed plants. It is also important to note that aphid infestations are typically patchy, and often heavier on crop edges. Ensure that crop sampling covers a representative area of the crop, with a minimum of 20 plants examined at 2-3 locations within the paddock.

Description

GPA have an oval shaped body, and may be pale yellow-green, orange or pink in colour. The adults are approximately 3mm long; winged adults have a black patch on the abdomen. Wingless forms are uniform in colour. Their presence on the underside of leaves is also diagnostic. For images of green peach aphids, click here.

 

* Sources of field reports of green peach aphids

Mick Duncan – Agronomist, Northern Agriculture (NSW Northern Tablelands)

Adrian Dunmore – Agronomist, Rodwells, (NSW Riverina)

Bill Kimber - PestFacts SA team, SARDI

Andrew McMahen – Agronomist, Landmark (Victorian Mallee)

Adam Pearce – Agronomist, Clovercrest Consulting (Victorian Wimmera)

Glen Smith – Consultant, Riverina Co-op (NSW Riverina)

Justin Whittakers – Agronomist, Landmark (NSW Riverina)

Kent Wooding – Agronomist, AgriVision Consultants (Victorian Mallee)