Aphids – Identification and Control

Aphids suck the sap from the stems of your plants and excrete a sweet honeydew onto the leaves and stems. They are one of the most common pests found in gardens and are also known as green or black fly.

They come in many colours – green, black, brown, pink, and even purple with black spots – ranging from 1mm to 5mm long. Clusters of aphids can be found on fresh young shoots, stems, flower heads, and under/on foliage.

Aphids reproduce at a phenomenal rate. Adult aphids can produce 5 young per day under the right temperatures, and those five can reproduce around five days later!

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Symptoms of Aphid Damage

• Stunted growth or curled leaves

• White or creamy scales on the foliage or at the base of the plant

• Large infestations can even kill a plant

• Trails of ants moving up your plant – ants are attracted to the sweet honeydew excreted by aphids, which can also lead to mould forming on foliage

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Control Methods

If you only have a few aphids, they can be wiped off with your finger, but keep a close eye on the plant as they can quickly return.

For a heavier infestation, aphids can be sprayed off using a hose, repeating the process as necessary. Another effective method is to spray an insecticidal soap directly onto the aphids. As the soap begins to dry, the aphids stick together and die of starvation. It may sound unpleasant, but it is far preferable to using chemical pesticides. Before spraying the whole plant, always test the soap on a small area first, as some soaps can damage certain plants.

Ladybirds are nature’s way of controlling aphids, so if you have an infestation, you’ll often find ladybirds close behind. Where possible, it’s best to leave them alone to do their job. Lacewings are another natural predator and are fascinating to watch, as they grasp aphids in their mouths and digest them. Ladybird larvae and lacewings can be purchased from some garden centres and online, although they can be expensive.

Please note that once biological controls have been introduced, insecticidal soap should not be used, as this will kill them as well. Ants will often protect aphids from predators because they rely on the honeydew aphids produce as a food source. If ants feel a plant is under threat or becoming overcrowded, they may even transport aphids to another plant. To prevent this, ant-killing bait can be placed around the base of the stem to stop them in their tracks. Sticky traps are also useful and can help catch other insects in the area.

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Prevention Tips

• Avoid over-feeding plants, which encourages the production of fresh shoots that aphids love.

• Use slow-release fertilisers to prevent over-stretching new growth.

• Never spray plants on very sunny days, as this can scorch foliage.