Diagnosing aphid damage in field peas

Small soft-bodied winged or wingless insects that damage field peas grown in Western Australia through transmission of viruses rather than direct feeding damage. Main species are pea aphid (Acyrthosiphon pisum), green peach aphid (Myzus persicae), bluegreen aphid (Acyrthosiphon kondoi) and occasionally cowpea aphid (Aphis craccivora). It is unusual for aphids to colonise field peas, typically as winged aphids move through the crop they may spread viruses. This page describes aphids whose host is peas.

What to look for

Plant

In the absence of virus, small stressed plants with aphids present on leaf undersides of older leaves.

Insect Adult

The pea aphid is up to 4 mm long, may be yellow, green or pink in colour. They have black knees and dark joints on their antennal segments. These aphids feed primarily on pea, faba bean and lucerne.
The green peach aphid (GPA) tends to be shiny or waxy, and ranges from yellow, through to green and pink. They can be similar in colour to young unfurled field pea leaves. GPA has a wide host range including canola, lupins and other pulse crops, and can also be found on weeds including wild radish, doublegee and blackberry nightshade.
The bluegreen aphid (BGA) is up to 3 mm long, and matt bluish-green. Large numbers of winged BGA fly from pastures to crops later in the growing season.
The cowpea aphid (CPA) has a black body and black and white legs, it is not typically found on field pea, but often colonises lupin and faba bean plants

Where does it occur?

Small numbers of aphids can survive the hot dry conditions experienced during summer if their host plants are available. Rainfall in late summer and early autumn encourages survival of aphid host plant material, leading to early aphid flights into crops soon after seeding.
Rainfall in late summer and early autumn rainfall stimulates plant growth before the crop growing season and provides hosts (clovers, weeds and volunteer crop plants) that encourage rapid aphid multiplication.
Lack of ground cover; sparse stands; poor canopy development; heavy grazing of nearby pasture; paddocks with large perimeter to area ratios, favour aphid movement into a crop.

Where did it come from?

Alternate host

Aphids have numerous generations throughout the year and survive outside the cropping season on alternative hosts including perennial pastures, volunteer crop plants and weeds.
CPA host range includes pasture medics, faba beans and tagasaste.
BGA host range includes prefers medic and sub-clover pastures, lupins and lucerne. legumes, and is a common pest of medic and sub-clover pastures.
Pea aphid host range includes lucerne, peas and faba beans.
GPA has a wide host range, and are often found on a variety of weeds including wild radish, wild turnip, doublegee and blackberry nightshade. Other crop hosts include canola and lupin.

Management strategies

Aphid colonies do not usually develop on field peas, control is only warranted if aphid colonies are impacting on the grown of the plant.
Correct identification of the aphids is critical. Green peach aphids are resistant to organophosphorus, carbamate and synthetic pyrethroid insecticides, and can be difficult to control. Green peach aphids are easily identified; they tend to be found on the underside of leaves and vary in colour from bright green to pink.
Spraying insecticides to stop virus spread is unlikely to be of any benefit because insecticides do not act fast enough to prevent the rapid spread of the virus by aphids and may increase rather than reduce virus spread because aphids move around more on sprayed plants.

Further information

Pulse Australia [1]