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Aphids on Conifers

In the South African garden, conifers can be seen as real assets as they come in all shapes and sizes, can be planted in a variety of climates, and are known to be drought & frost tolerant.

They are also brilliant for planting close to walls, paving and swimming pools as they do not have an opportunistic root system.

Conifers have grown a bad reputation over the last decade or so due to these trees suddenly starting to turn brown and then eventually die back. This condition can be attributed to conifer aphid infestation during the autumn and winter months. They occur as soon as the temperatures start cooling down and can then rapidly increase in number.

The first signs of an infestation would be yellowing of foliage as they suck the sap from the tree branches. You will discover them on the main stems and branches of the tree and not on the new soft growth (like with other aphid species), making them more difficult to spot. The aphids secrete a honeydew substance which makes the tree’s branches sticky. The honeydew in turn then attracts ants that protect the aphids from their natural predators in exchange for honeydew. Sooty mould can also start growing on this sticky substance, turning the branches black.

Conifer aphids do have many natural predators like ladybirds, certain wasps and chameleons that can keep their population in control. If an outbreak occurs there are a few methods that can be used to decrease the population:

1. Spraying the tree down with a strong stream of water to wash the aphids out.
2. Controlling any ant populations surrounding the trees.
3. Spot spray with organic Pyrethroid based insecticide. It is best to try and let the insecticide just run down the stems and branches to avoid spraying and killing any of your natural predators.
4. If a large infestation does occur, do a once off treatment with organic insecticides combined with organic horticultural oils. Look for products that will not kill your natural predators.
5. If you are not an organic gardener, regular treatments with insecticides formulated for the control of aphids are recommended.

 

 

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