As the weather warms up in spring, it’s important to keep a close eye out for sap-sucking aphids. Mild weather will result in greenfly, blackfly and other members of this troublesome family of bugs visiting gardens. They need to be dealt with as soon as they are spotted - aphids breed at a ferocious rate and one or two can quickly become a colony.
What aphids do
Apart from gorging on the sap of plants, leading to loss of vigour, curling leaves and distorted stems, aphids are behind other plant problems. They can help to spread viruses from one plant to another and their sticky excrement or honeydew, makes the ideal surface for sooty mould fungus to develop. This black fungal growth can coat leaves and stems, checking growth by preventing light and air reaching the plant.
Where to spot them
Aphids are not particularly discerning and love many plants. This includes vegetables, such as broad beans and lettuce, many perennials and lots of shrubs – they seem to be particularly fond of roses and philadelphus. Look under leaves at the top of plants, flower buds and on young, developing shoots.
How to control aphids
If you spot them early enough, you can halt them in their tracks by simply rubbing them off with your fingers or by pinching off an infested shoot to the nearest, aphid-free bud - don’t be tempted to compost the debris, the best place for it is the dustbin. However, if they’ve been on the plant undetected then you can expect larger numbers which makes controlling by hand difficult.
To despatch large populations quickly and effectively you will need to spray. Although there are many chemical pesticides available in garden centres and DIY stores, try using an insecticidal soap, such as Savona, or a spray derived from plant extracts.
You don’t have to resort to pesticides to control aphids. Biological controls have become increasingly popular, especially among those who garden organically. In the greenhouse you can introduce naturally occurring predators and parasites, while outside you can boost the number of aphid eating creatures in your garden by releasing more ladybirds and lacewings. These both have a voracious appetite for aphids, with a single lacewing larvae able to eat over 300 before it changes into an adult.