Hemiptera : Aphididae

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Aphids are sap-sucking insects related to psyllids, whitefly, scale insects and mealybugs. Aphids are major pests of ornamental and productive plants, and some species (such as Green Peach Aphid) may spread viral diseases between plants.

If the weather is warm and moist, and food is abundant, the conditions are ideal for Aphid numbers to build rapidly. There are about 175 species of Aphids in Australia, and the vast majority of them are introduced species. You are more likely to find Aphids on vegetables and exotic ornamental plants than on native plants.

Best Treatment for Aphids

Aphids are difficult to control if you allow their colonies to build up into huge numbers. You need to keep an eye on your plants to spot Aphids, or evidence of Aphids, early (see Monitor).

Prevention is always better than cure. There are several things that you can do to prevent or minimise Aphid damage (see How to Prevent Aphids Appearing). The trick is to not let them build up in such high numbers that they are causing major damage (see Symptoms of Aphids).

A healthy garden will have a healthy population of Aphid natural enemies, therefore, beneficial insects. The most efficient of these are the little wasps that turn Aphids into ‘mummies’. If you find an Aphid colony it is a good idea to give these parasitic wasps a chance to do their thing before spraying or brushing off the Aphids (see beneficial wasps).

Predators such as hover fly larvae, lacewing larvae and ladybird beetles are also quite efficient and can decimate an Aphid colony in less than a week.

If treatment is required, spray with Yates Nature’s Way Vegie & Herb Spray. It’s ready to use and perfect for use on vegies, herbs, fruits and ornamental plants. There is no withholding period, so you don’t have to wait to eat vegies, fruits or herbs – simply wash before eating. For large infestations on multiple plants, use Yates Nature’s Way Vegie & Herb Spray Concentrate. The concentrate can be mixed and diluted in a sprayer to make up larger volumes of the ready-to-use spray. It does not keep for more than 24 hours, so only make up what is required.

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Image above: Aphids attacking new growth of rose
(Image courtesy of Elise Dando)

What are Aphids &
How to Get Rid of Them

Aphids are common garden sap sucking pests. They can cause damage directly through their direct feeding or indirectly as vectors of plant viruses. Aphids excrete honeydew, which may cause a build up of sooty mould and attract ants.

There are about 175 species of Aphids which occur in Australia and the vast majority are introduced (i.e., not native to Australia). Common pest Aphids include Black Citrus Aphids (Toxoptera spp.), Black Peach Aphid (Brachycaudus persicae), Cabbage Aphid (Brevicoryne brassicae), Green Peach Aphid (Myzus persicae) and Rose Aphid (Macrosiphum rosae). All these Aphids are introduced pests.


Description

Aphids are small pear-shaped sap-sucking insects usually less than 3 mm long, which may be winged or wingless in the adult form. Nymphs are typically miniature versions of the adults but without wings.

Adult Black Citrus Aphids are shiny dark brown to black Aphids about 2 mm long. They infest blossoms and young growth of citrus trees.

Adult Black Peach Aphids are glossy black Aphids about 1.5 mm long. Black Peach Aphids nymphs are brown. These Aphids tend to cluster around blossoms and young growth of peach and nectarine trees.

Adult Cabbage Aphids are about 2.5 mm long, are greyish to light green in colour, and covered with a mealy waxy substance. Cabbage Aphids typically form tight clusters on the upper surfaces of leaves and flower stems of brassica plants.

Adult Green Peach Aphids are about 2.5 mm long and vary in colour from yellow to pale green to pinkish. Green Peach Aphids may form clusters of hundreds of individuals on a vast range of plants.

Rose Aphids are about 2.5 mm long, and are green, pink or brownish orange in colour. All colour forms may be present at the same time. They typically form clusters on rose buds.


Life Cycle

Aphids typically develop through a life cycle of gradual metamorphosis. Depending on the species adult Aphids may lay eggs some of the time and lay live young at other times, or not lay eggs at all. Many Aphid species are capable of reproducing without males (i.e., they reproduce parthenogenetically). Aphid colonies can increase in size so rapidly because female Aphids mostly lay live young and can do so without having to mate.

Wingless adults are the norm when the colony is not overcrowded. Winged adult Aphids develop when a colony must migrate from an over-wintering site, or from drying plants, or when conditions become too crowded.

Aphids typically pass through 4 nymph stages (instars) before the adult stage. As they moult, they leave behind their old skin casts that are easily visible in Aphid colonies as white objects. Aphid life cycles can be completed in 10 to 14 days in warm weather, and there may be more than 20 generations per year depending on the climate and the species.

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Image above: adult female (left) and nymph (right)

What Plants are Impacted by Aphids

Some Aphid species feed on a specific plant, or groups of plants, while others feed on a wide variety of plants.

  • Black Citrus Aphids mostly feed on citrus but may also attack camellia and coffee plants.
  • Black Peach Aphids feed on stone fruit including peaches, nectarines, plums and apricots. Black Peach Aphids avoid the heat of summer by moving down the tree and feeding on the roots. They move back into the canopy in autumn.
  • Cabbage Aphids feed on brassicas, including cabbage, turnip, broccoli, Brussels sprouts, cauliflower, common stock, and weeds such as wild turnip and wild mustard.
  • Green Peach Aphids feed on a wide range of plants including stone fruit; vegetables such as beans, brassicas, lettuce, potato, spinach and tomato; ornamental plants including dahlias, geraniums, poppies and roses; and weeds such as capeweed, dock and sow thistle.
  • Rose Aphids feed on roses.

Symptoms of Aphids

  • Distorted leaves and leaf drop.
  • Wilting and stunting of seedlings.
  • Wilting of shoots.
  • Failure of fruit set. Fruit drop.
  • Aphids excrete honeydew, which may promote the growth of sooty mould and attract ants.
  • Leaves may be covered in unsightly white Aphid skin casts.
  • Green Peach Aphids can transmit plant viruses such as potato leaf roll virus and several mosaic viruses.
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Image above: Aphid exoskeletons or 'skin casts' shed after moulting
(Image courtesy of Elise Dando)

 How to Prevent Aphids Appearing

Monitor

  • Check susceptible plants while watering the garden or weeding. Look for clusters of small pear-shaped insects and sooty mould or ant activity.

Prevent

  • Ants may protect Aphid colonies in return for a feed of honeydew. You can prevent ants from climbing into trees by banding the trunks with horticultural glue.
  • Trap Black Peach Aphids moving up and down the tree trunk by banding the trunk with horticultural glue.
    Some Aphid species breed in weeds. Control weeds.

Natural enemies

  • Parasitic wasps (see beneficial wasps) cause Aphids to turn into shell-like ‘mummies’. They may be bronze coloured or black depending on the wasp species.
  • Hover fly larvae, lacewing larvae and ladybird beetles are the main predators of Aphids.
  • Wasps and predators are very efficient at controlling Aphids. If you find Aphids on your plants, wait a week to see if the natural enemies control them for you. If they don’t control the Aphids, then you can take action.

Recommended products to control Aphids


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