There are a number of commercially available pesticides that are certified for use in organic gardening, but it is also possible to make effective pesticides and deterrents using ingredients from your local grocery or health food store, or from what you have in the garden.
We often prefer to make our own treatments and sprays because
Care needs to be taken when using any of these treatments as in some cases they will harm beneficial insects as well as pests. For example, the larvae of hoverflies and lady beetles, which feed on soft-bodied insects such as aphids, also have soft-bodies and will be affected by contact sprays.
To minimise the effect on beneficials:
Many pests come out only at night, so trapping them can be achieved with the following practices.
Use food stuffs to attract the pests
Leave a bucket of water under outside lighting.
Shallow containers of sugar water, honey, beer or dried yeast will also trap many pests.
Usage: Deters many pests
Source: Collected individuals of the same species or family. In the case of caterpillars, it is alright to use those that have been affected by Bt spray.
Preparation: Take approximately ½ cup of the pest you are targeting, grind them up, and place in a bag made of cheese cloth or a similar material that will allow water to soak through. Cover with water and soak overnight. The resulting brew will be strong, so only a little needs to be used; 10 ml to a 10 L watering can.
To make a smaller measure, use 1 teaspoon of bugs soaked in 2 cups of water.
Application: Spray on the same type of pest that the bug juice was made from.
How it works: All insects carry their own pathogenic diseases which, when juiced and sprayed on infested plants, will provide a biological control. Also, being able to detect dead individuals of one’s own species often acts as an alarm, deterring new individuals.
Usage: Aphids, snails, codling moth, white butterfly, caterpillars, wireworm and ants.
Preparation: Boil 250 g of chopped chillies (with the seeds) in 1.5 litres of water for 10-20 minutes. Dilute in 1.5 litres of water and allow to cool. Strain. Quantities can be varied to change the strength of the spray, however if it is too strong it may burn the leaves of plants.
Application: Spray directly onto pests and also on plants as a deterrent. Do not spray in direct sunlight as this will increase the risk of burning the plant. Spray weekly or more often if it rains.
How it works: It may be the capsaicin in chillies which harms pests or perhaps it’s just the smell and taste that they don’t like. Boiling the chillies extracts the capsaicin.
Effect on beneficials: This spray is harmful to bees.
Comments: Garlic and chilli are a good combination. See the information on garlic below.
Usage: Wide range of pests
Preparation: Boil 100 g of dried flowers in 1 L of water for 20 minutes, then strain.
Application: Spray directly onto pests.
How it works: This is the flower that produces the pyrethrum chemical (see the information on pyrethrum in the entry on commercially available treatments). Combine with neem oil to give more protection to the plant.
Effect on beneficials: It will also harm beneficials if they are sprayed.
Comments: This preparation will only last 2 months after preparation, after which time it loses its potency.
Usage: Slugs and snails
Source: Any used coffee grounds e.g. home plunger or filter, or ask your local cafe. Instant coffee is not strong enough.
Preparation: Add 1 part coffee grounds to 10 parts very hot water, stir, and allow to stand overnight. Pour off liquid and dilute to a maximum of 1 part liquid to 5 parts water- it will not be as effective if it is too weak.
Application: Pour around plants.
How it works: It is the caffeine that gets them. They absorb it as they slide over the coffee- a little will repel them and more will speed up their metabolism so much that it kills them.
Comment: The coffee grounds can be spread directly around plants but they can make the soil more acidic so it is best to dilute them using the method described above. Plants which like a lower pH (e.g. strawberries) will be fine with scattered coffee grounds.
Coffee grounds also contain nutrients that will benefit the plants.
Usage: Grasshoppers and caterpillars.
Preparation: Use dry or as a paste of flour and water.
Application: Smear paste over leaves, or dust dry flour over the pests if you can. Dry flour dusted on leaves will be blown away.
How it works: Caterpillars- dry flour will suffocate and dehydrate them.
Grasshoppers - paste gets over them and will suffocate them as well as slow them down, making it easier for birds and other predators to catch them
Effect on beneficials: Beneficials may also get bogged down with the paste.
Usage: Aphids, snails, codling moth, white butterfly, caterpillars, wireworm and ants.
Preparation: Soak 4 crushed cloves in a litre of water for several days. For a more potent spray use 2 garlic cloves and 6 chillies added to a litre of water with 2 tablespoons of pure soap, preferably a potassium-based one (not detergent). Strain and dilute this in 5 litres of water.
These quantities can be varied to make a stronger or weaker solution.
Application: Spray directly onto pests and on plants as a deterrent. Do not spray in direct sunlight as this will burn the plant.
How it works: The strong odour and taste of garlic make it a really effective repellent,. If your spray is strong enough it will kill the small soft-bodied pests.
Effect on beneficials: Could also be harmful to beneficial insects if they come in contact with it.
Comments: Nettles, basil and wormwood can also be added to the mix. Use hot water to bring out their compounds as you would for a tea.
Usage: Many insects are repelled by specific herbs e.g. basil will repel aphids, peppermint will repel ants. See information in plants section for more examples.
Preparation: Gather a couple of handfuls of leaves and place in a saucepan, cover with boiling water (for larger quantities – 500 g of plant in 5 litres of water) and soak for a few hours. Cover with the saucepan lid so that the oils do not evaporate. Allow the liquid to cool and add a small amount of detergent, then dilute to 1 part tea to 4 parts water.
Application: Spray where the pest insect is likely to be.
How it works: Will act as a deterrent to the insects that don’t like that particular herb.
Comments: It is possible to buy an essence or oil extracted from some plants, which will work just as well. Use 10-15 drops in 1 L of water.
Usage: Spider mites, aphids, and other soft-bodies insects.
Preparation: Mix equal parts full cream milk and water.
Application: For mites, spray on plants, making sure to get right into the centre of the plant where the mites hide. This needs to be done every few days as they breed very quickly. For aphids, monitor how effective it is and spray as needed.
How it works: Milk will kill the mites and smother the aphids.
Effect on beneficials: It will also harm hover fly larvae.
Comments: The milk may leave a white film on the leaves but this can be washed off.
Milk obtained direct from the farmer is good to use as a fungal spray, especially on powdery mildew. Yoghurt can work well too as it will also have the beneficial cultures.
Usage: Caterpillars, butterflies and moths, nematodes.
Source: Some grocery and health food stores. Produce stores and co-operatives should also stock it.
Preparation: Mix 2 tablespoons of molasses with 1 litre of water. Allow to cool and add a small amount of detergent.
Application: Spray on leaves. Soak the ground around plants for nematodes.
How it works: It is a mild insecticide. Caterpillars will drop off the plant while butterflies and moths will be deterred because it is sticky.
Effect on beneficials: Earthworms may be adversely affected.
Comments: Molasses will feed the beneficial bacteria in the soil, allowing their numbers to increase and, in turn, help balance other micro-organism ratios, thereby reducing the nematode population.
Nicotine is often included as a home-made insecticide treatment, along with tomato leaves, which are related.
I have not included them as I believe they are too toxic.
Usage: Repels red spider mite and aphids.
Preparation: Blend onions with skins until they reach a milky consistency. Dilute this by half.
Application: Spray on plants regularly as a repellent.
How it works: Insects don’t like the taste or smell.
Usage: Slugs, snails, mealy bugs, aphids and other soft-bodied insects. Lemon peel works for whitefly.
Preparation: Chop or blend the peel from 1 orange, add 2 cups of boiling water and soak for 24 hours. Strain liquid and add a small amount of detergent.
Application: Spray directly onto pest or on plants.
How it works: As a contact spray, it destroys the waxy coating on scale and mealy bugs.
Usage: General deterrent.
Preparation: Buy ground or freshly grind your own as this may be stronger.
Application: Can be sprinkled around plants ‘neat’, or combined with flour to help disperse it.
How it works: Insects don’t like the smell or taste of it.
Effect on beneficials: Harmful to bees.
Comments: Pepper is also a natural antibacterial.
Quassia chips are bark chips from the Quassia tree (Picrasma excelsa), native to the West Indies.
Usage: Kills flies, red spider mite, aphids, caterpillars, small beetles and nematodes.
Source: Nurseries, horticultural stores.
Preparation: Add 1 tablespoon of quassia to1 litre of water, soak overnight, then bring to the boil and simmer for 30 minutes.
For aphids dilute 1 part quassia solution in 5 parts water.
For caterpillars dilute and 1 part quassia solution in 4 parts water
Application: Spray on the ground around plants or directly onto leaves. It is not a good idea to spray the parts of the plant you want to eat as it is extremely bitter.
How it works: It is an insecticide that affects sucking and chewing insects. It will also act as a contact insecticide.
Effect on beneficials: Don’t spray directly onto beneficial insects as it will harm them.
Comments: It will also repel possums.
Rhubarb makes a very potent insecticide but it should not be used on food crops because of its toxicity.
I have not included it for this reason.
Usage: Aphids and sucking pests.
Preparation: Dissolve 250 g of common, pure laundry soap in 10 litres of water. If using a liquid soap (make sure it doesn’t contain chemicals), mix 5 tablespoons with 4 litres of water. Boiling water will dissolve the soap easier.
Application: Spray on pests in the early morning or late afternoon as the liquid will not dry out as quickly as in the midday sun.
Hose the soap spray off shortly after spraying as the soap will damage the foliage. Repeat if the aphids still look lively.
Eggs may not be affected, so it could be necessary to spray again after a week to break the reproductive cycle.
How it works: It dissolves the waxy external skeleton of the pest.
Usage: Insects in general.
Preparation: Soak used tea leaves in water for a couple of days. Strain liquid.
Application: Spray foliage as well as the soil around plants. Do not put on plants that like more alkaline soil as it is acidic and may lower the soil pH.
How it works: Natural insect repellent.
Comments: The tannin and nutrients in tea are also good for plants.
Usage: Sap-sucking and leaf-eating insects such as aphids and scale. Also mealy bugs and caterpillars.
Preparation: Shake or blend 500 mL of vegetable oil (sunflower or coconut oil are good) with 125 mL dish washing detergent until mixture is combined and turns white. Dilute 1 part white oil to 10 parts water.
Application: Spray directly onto pests. Avoid using it in hot weather or direct sunlight as it will burn the foliage. Don’t use too often as it will block the leaf pores hindering the growth of the plant.
How it works: Suffocates insects by blocking the pores (spiracles) that they breathe through.
Comments: This mixture will keep for 3 months. Horticultural oil is the commercial equivalent.
Usage: A variety of pests, especially snails.
Application: Sprinkle around plants sparingly as it usually contains salts which could harm the plants. The lime it contains will increase the pH of the soil, so do not sprinkle around plants that prefer low pH or if the soil is already alkaline. It also contains potassium.
How it works: A good deterrent, especially for pests such as snails that would have to “slide” over it.
To make a liquid version which can be sprayed out:
Usage: Deters leaf-eating pests
Preparation: Mix ½ cup of wood ash with ½ cup of lime. Add to 4 litres of water and stand overnight. Strain
Application: Spray onto the tops and under the leave of infested crop.
Comments: Both wood ash and lime will raise the pH.