Peter Dowdall: Use natural balance to keep greenflies and other aphids in check

Once more, as with all pest problems in the garden, I always, first go back to the “natural balance”. Put simply, the natural balance means that by ensuring a wide variety of species in the garden, both plant and animal, we can prevent the unnatural build-up of any one species.

Maintaining this balance is probably the most important thing that we can do in the garden, from both an environmental point of view and also to get the best results in the garden. One of the most effective, organic ways to control aphids is by attracting beneficial insects that feed on them.

Ladybirds and hoverflies are natural predators of aphids. Planting flowers such as daisies, marigolds, fennel, dill, and yarrow can help attract these beneficial insects to your garden. Creating a diverse and balanced ecosystem will encourage natural predators to thrive and keep aphid populations in check.

If we go out and spray some nasty chemical on the plant with the aphids, we will inevitably destroy or diminish the population of predators also. The aphid population will increase in number once more, far quicker than that of the predators. Thus, we have interfered with the natural balance and left a predator-free garden open in which aphids can thrive.

Perhaps the simplest thing of all to do is to just use water. Using a strong spray of water from a garden hose can physically dislodge aphids from plants. Spray affected plants, focusing on the undersides of leaves, where aphids tend to congregate. Regularly rinsing plants with water will help prevent aphid populations from establishing and spreading.

Simply pruning off stems and leaves which are affected is a very effective and instant control method but not always suitable if the entire plant or large parts of the plant are infested.

Regularly inspect your plants for signs of aphid infestation, such as curled leaves or sticky honeydew residue, and take pruning action quickly to prevent their spread.

Companion planting is another organic method of maintaining the natural balance in your garden, by growing certain plants together to enhance growth and deter pests. Certain plants can repel aphids and act as natural deterrents whilst others are strongly scented, which results in confusing the pests. 

For example, planting aromatic herbs such as mint, coriander, and dill near vulnerable plants can help repel aphids. Also, interplanting flowers such as nasturtiums and petunias can attract aphids away from the plants you want to protect, acting as a sacrificial trap.

There are many examples of homemade spray remedies which I have heard over the years and some if not all of these can be effective in controlling aphids without the use of harmful chemicals. 

One simple recipe involves mixing one tablespoon of washing-up liquid with one litre of water. Spray the solution directly onto the affected plants, ensuring it reaches the undersides of leaves where aphids often hide. The soap suffocates the insects, disrupting their life cycle. Repeat the application every few days until the aphids are under control.

Garlic wash

I prefer to try to prevent them from attacking the plant rather than killing them, however, as the ladybirds and hoverflies do need a food source, and one of the best ways of all is to apply a garlic wash.

Using two or three garlic bulbs per litre of water, peel and pulp the garlic cloves to release their oils and active compounds. Mix the — admittedly smelly — pulp with one litre of boiling water. Allow the mixture to steep for at least 24 hours. This will allow the beneficial compounds in garlic to infuse into the water. Then strain the mixture to remove any solid particles or garlic remnants, and the resulting liquid is your garlic wash.

Further dilute this mixture with water before spraying it onto your plants. I use about a cupful of this mixture to a 1.5-litre spray gun. Before using the garlic wash, test it on a small area of your plants to ensure they are not sensitive to the solution and if they are, then you can dilute with more water to weaken the concentration.

Reapply the garlic wash every few days or after rainfall to maintain its effectiveness. Don’t spray the solution on plants during hot and sunny periods, as it may cause leaf burn due to the concentration of the garlic’s active compounds. Using garlic in this way means that you are also improving the plant’s overall health as the anti-fungal and anti-bacterial properties of garlic are also transferred to the plants.

• Got a question for Peter Dowdall? Email gardenquestions@examiner.ie