Aphids, also known as greenfly or blackfly, are small, pear shaped, plant eating insects about 1/10 inch long. They come in many colors but the most common are green, black or yellow. They infest a wide range of plants from fruit and shade trees to ornamentals, flowers and vegetable plants.
Aphids feed in clusters preferring new shoots and young leaves and are commonly found on the underside of the leaves. They feed by sucking up the plant juices with a needle-like mouthpart and some inject toxic saliva into the host. They are seasonal pests and may occur in large numbers for a relatively short time, mainly in warm humid weather.
Effect on plants
Aphids cause leaf curl, twisted and distorted foliage, wilting, yellowing or browning, stunting of growth and a general decline in the vigor of the plant due to the removal of the sap. They often transmit disease-causing organism like plant viruses to the host.
Aphids produce honeydew, a clear sticky dropping that lands on leaves or any surface below where the aphids are feeding. These objects then become covered by brown or black fungi and this is often the first sign that aphids are present. If this covers leaves then it can block out light which is essential for photosynthesis.
Colonies of aphids are sometimes protected by some species of ants and in return, they are allowed to collect the honeydew.
- Simply squashing with the fingers can be effective if the colony is not too large
- Dormant oil can be sprayed on fruit trees in spring to kill overwintering aphid eggs
- Summer oil works well but needs to come into contact with the insects to be effective
- Spray the underside of plants where clusters of aphids are found with strong jets of water to reduce the numbers
- Use a soap spray either a commercial one or make your own, 1-2 tablespoons of non-detergent soap in 1 gallon of water (10-25ml in 4l)
Prevention is better than cure so ensure you have strong healthy plants which will be more resistant to aphids and other pests.