Nature’s Own Repellents

We can reduce our dependency on insecticides by using natural plants to control pests.

With the current crop of scientific research coming out pointing towards a massive decline in the numbers of some insect species (by as much as 40%!), we should all be very worried. The decline in insects’ numbers has been directly linked to several factors: climate change, mono-cropping, pollution of waterways and, obviously, the reliance on pesticides, to name but a few. Fortunately there are some sound environmentally friendly ways in which we can fight pests. 

Natural chemical factories

Many plants produce chemicals that act as natural repellents to protect them from the unwanted attention of insects. We can exploit these to our benefit by planting them amongst crops to ward off pest species.

Some plants will not only repel surface pests, but their root system may be effective in repelling soil pests such as nematodes and moles. For example, French marigolds not only repel whitefly, but also nematodes. Some nematode species can attack a host of commercial crops such as potatoes, in many different ways.

Examples of repellent plants:

To repel nematodes: Plant chrysanthemums, dahlias and french marigolds.

To repel slugs and snails: Plant fennel, petunias ad rosemary.

To repel spider mite: Plant coriander and dill.

To repel mice, moles and rabbits: Plant artemisias, Mexican marigold, mint and onions.

Push-pull technique

Another very effective technique that we can employ is known as ‘push-pull’. The technique is a proven, ecologically based method of pest management. It was first introduced in Kenya in 1999 to increase the poor maize yields due to stem borer infestation and has subsequently been adopted by over 100 000 farmers.

So, what is push-pull? In a nutshell, it is the simple practice of inter-cropping with plants that repel a specific pest, while at the same time planting plants that act as decoys to lure the pests away from the crops. So one plant is ‘pushing’ pests away while another is ‘pulling’ them away. The decoy plants are important as they give the pests somewhere to go, and these plants can then be dealt with in a more robust manner. Decoy plants are usually planted along the borders of the main crop to draw the pests well away.

Push-pull not only decreases insect pests, thus producing higher crop yields, but has also been found to increase soil quality and fertility. One study found that those farmers using the push-pull method saw their crop yields grow from 1 ton to 3.5 tons per hectare, with no chemical intervention or extra work of their part. This resulted in a significant increase in revenue.

Examples of push pull technique

Strawberries: to combat slugs and snails.

Push: Thyme

Pull: Pole Beans

Tomatoes: To combat whitefly.

Push: Broccoli, cabbage, peppers

Pull: Asparagus, mint, mustard

Peppers: To combat aphids, thrips and leaf hoppers.

Push: Geraniums

Pull: Sunflowers

Rotate crops

If you are consistently having problems with pests year on year, one of the easiest ways of beating the problem is crop rotation, which falls under the banner of cultural control. The adoption of cultural control, particularly where crop rotation is concerned, is to break the lifecycle of that particular pest. For example, in Africa, maize weevil can wreak havoc with maize crops. So by planting maize one year and sorghum the next, we break the weevils’ food-chain, and that of related pests that may be lying dormant in the soil. The following year the pest has nothing to feed on. Subsequent ploughing at the beginning of the growing season will bring to the surface any dormant pests, which predators such as birds will finish off.

Crop rotation, then, is essentially planting unrelated crops bi-annually, to break a feeding cycle. Another example could be if you crop tomatoes and are blighted by tomato worm, to plant peppers or onions the next year. Onions are a particularly good crop to plant to break the cycle of both airborne and soil- borne pests, as they produce a very effective natural repellent.

Tail-end

For the sake of our insect friends, and the environment as a whole, when dealing with pest species we should go out of our way to use more friendly approaches in their control. None could be more safer, or easier, than to use plants themselves. Inter-cropping and push- pull are proven techniques that can yield more fruitful harvests.

A knock-on effect of using these techniques is that many of the plants you use also repel mosquitoes. I have marigolds at the front of my house, which I planted to attract butterflies, and while I’m weeding there, I suffer little from mosquitoes or flies. If a walk around to the rear garden, they are lined up in rows to exact vengeance.

*While catnip makes a good pest repellent, it is attractive to cats, so while you probably won’t be bothered by insects, the local strays may take up residence in your garden.