Whether it be greenfly, blackfly or woolly aphid, aphids are sap-sucking pests that will happily eat most garden plants, particularly in greenhouses. Throughout the summer, they will have attacked younger shoots, often at the tips of plants, in colonies which can quickly ramp up in number, causing distortion, discolouration and general mayhem.
The old ruthless adage of “if it flies, it dies” is no longer appropriate; we need to garden in harmony with nature, and I believe that includes learning to strike a balance when the aphids arrive.
They are a valuable food source for many insects and birds, which will tend to control numbers to an extent – as gardeners we should only step in when a real infestation is on the cards.
Why is aphids eating plants a bad thing?
Aphids feed on the sugary sap found in plant tissue. Any excess sugar is then secreted by the aphid’s body, hence that tacky layer on the surface of leaves. (Sooty mould is often a secondary problem on leaves, resulting from those sugary deposits.)
Viruses can also be spread by aphids, making cucumbers and tomatoes vulnerable in a small greenhouse.
It is relatively easy to reduce infestations. Winter washes can be used on fruit trees during the dormant months to deal with overwintering eggs on garden trees. In spring and summer, I use SB Plant Invigorator to control aphids as soon as I spot an outbreak: you only need to spray the top third of the plant as most sap-sucking pests will inhabit those areas, which leaves the lower parts of the plant to natural controls such as parasitic wasps.
If you’re growing for the table, be aware that some insecticides are not suitable for edible crops – read the label carefully to ensure that the product is safe for the plant, you and the other animals that share our gardens.
If you use a spray, avoid bright sunshine, which will cause scorch on the young leaf. But simply running your thumb and forefinger down a plant stem once a week is pretty effective.
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