Aphids are one of the most common and best known garden pests. But how much do you really know about these insects? How should you deal with them in your polytunnel garden?
What Are Aphids?
Aphids are small sap sucking insects in the Aphididae family. There are thousands of different species, and several hundred that can be a problem in a garden. These tiny creatures are less than 1/8th of an inch in size. But their numbers mean that together, the damage they can do is surprising for something so small. Common names for these insects include greenfly and blackfly, though they can also come in other colours, depending on the distinct species.
Why Are Aphids a Problem in the Garden?
Aphids are one of the most destructive pests in temperate climate gardens. They can weaken plants by sucking sap. Sometimes they can kill them outright. They will generally cluster on young, fresh green growing tips and new foliage. You may first notice a problem when you see new growth that is stunted or deformed. Look closely, and tiny aphids will be visible on the plants.
If a problem is bad enough, a plant can eventually begin to lose its leaves and may wilt and die.
Unfortunately, aphids can also act as vectors for a range of plant diseases, spreading viruses and other diseases between the plants upon which they feed.
The Lifecycle of Aphids
Typically, aphids have a life cycle that involves flightless females giving birth to live nymphs. Oddly, those nymphs may already themselves be pregnant (think Russian dolls). This is sometimes referred to as telescopic development. No males are needed for this stage. Of course, this form of reproduction means that the number of insects can grow extremely rapidly. Nymphs mature into adults in around 10 days.
Males are born in the autumn, and mate with the females. Eggs are produced that will overwinter, then new females will hatch out in the spring.
One fascinating thing about aphids is that they are sometimes ‘farmed’ by certain ant species. Ants ‘milk’ the aphids by stroking them with their antennae, and herd them onto certain plants.
Dealing with Aphids in Your Garden
Remember, prevention is always better than cure. Plants that are healthy and well cared for are less likely to suffer problems with aphid attack.
Small numbers of aphids may not be a massive problem. But larger infestations in your polytunnel could mean that you lose a range of plants. Here are some of the steps you can take to deal with them when things get out of control.
Removing Pests By Hand
Sometimes, you can deal with a current, intense aphid infestation simply by removing them by hand. While this can be a time-consuming and challenging business, it is still an option that you could consider before using an organic pesticide.
Attracting and Protecting Beneficial Wildlife
Rather than looking for a way to kill pests plaguing your plants, it can often be better to think about how we can attract beneficial creatures that will help to keep their numbers down.
You can attract beneficial wildlife, and keep it in your garden, by planting the right things. For example, if you have an aphid problem, planting to attract ladybugs and lacewings and other predatory insects can be the best idea. You can also attract wildlife by creating and maintaining a range of different habitats, and leaving some wilder corners in your outside space.
Aphids are eaten by:
- birds (like swifts, for example)
Attract ladybirds and other beneficial insects to your garden by planting to attract them with, for example:
- marigold (Tagetes)
Repelling Pests With Scents
When working in an organic garden, it is important to distinguish between killing insects, and repelling or deterring them. The latter is generally a far better option. You can repel pests with:
- Companion plants.
(Garlic, for example, can not only be used to make insecticide. It can also be planted alongside other crops, where its smell can deter and repel a range of pest species.)
- Essential oil sprays.
(As well as planting herbs and flowers as companion plants, you can also consider using essential oils (appropriately diluted) as insect repellent. For example, to repel cabbage looper caterpillars, add a few drops of rosemary essential oil to a spray bottle of water and spray it onto your cabbages or other crops. Note – strong mixes of essential oils can be used as an insecticide to kill insects. But lower concentrations will work better in an organic garden as they will simply encourage aphids to stay away.
Organic Insecticides for Extreme Aphid Infestations
If a localized aphid infestation is really out of control, it is still important to avoid using synthetic insecticides. In extreme cases, we can turn to organic solutions like:
- neem oil
- Epsom salt sprays
- Castile soap (or other natural soap) sprays.
Such solutions, however, should be viewed as the ‘nuclear option’ when it comes to pest control. If overused, these can often make matters worse.
Why You Do Want Some Aphids Around
Remember that eradication of aphids all-together should not be your goal. Getting rid of a pest species can actually make problems worse long-term. Without the pest species to prey on, numbers of predatory creatures can decrease. This can cause a boom in the pest species population in future, as these creatures won’t be there to keep their numbers down.
Just because something is ‘organic’, that does not necessarily mean that it will help create a balanced and thriving garden ecosystem. Even organic pesticides are designed to kill insects that are plaguing your plants.
Unfortunately, they do not usually only kill the insects that are a pest. They also often kill other insects that come into contact with them. This includes those insects that prey on pest species and help to keep their numbers down.
In the longer term, therefore, using a pesticide of any kind – even organic – can actually make matters worse. If natural predation drops, pest numbers can increase. You risk making an imbalance in the natural system even worse.
Organic gardening should be all about balance. You may lose the odd plant to pests. But overall, when you have a good balance in an ecosystem, pest species will be at manageable levels. Predatory insects and other wildlife will help naturally to keep aphid numbers down.
Plants to Attract and Trap Aphids
Using trap crops can help you encourage aphids in your garden into areas where they are less likely to do damage. Sacrificial trap crops will attract aphids, and will be chosen in preference to other plants that you want to keep safe.
(Place these trap crops at some distance from the plants you want to protect from aphids. These attract the aphids and will keep them away from food crops.)
Using trap crops is one more strategy you can employ in an organic garden to keep things in balance and avoid too many plant losses.
Do you have aphids in your polytunnel? How have you managed them? Let us know your tips and suggestions in the comments below.
Elizabeth Waddington is a writer and green living consultant living in Scotland. Permaculture and sustainability are at the heart of everything she does, from designing gardens and farms around the world, to inspiring and facilitating positive change for small companies and individuals.
She also works on her own property, where she grows fruit and vegetables, keeps chickens and is working on the eco-renovation of an old stone barn.
To get in touch, visit https://ewspconsultancy.com.