Many natural remedies have not been scientifically tested or evaluated conclusively. Their popularity suggests they work but the degree of success is unknown, so it is best to treat them as tools to reduce pests and diseases rather than to eradicate them completely.
The following popular natural pesticides are commercially available.
Garlic spray for aphid infestation
Products, which are commercially available contain either pure garlic concentrate, or additional ingredients such as piperonyl butoxide and pyrethrins. Consult your local nursery or chemical retailer for more details.
Use a wetting agent to help the liquid to adhere to the plant. The garlic acts as a general deterrent and the additional use of white oil may suffocate the aphids.
Chilli spray for soft-bodied insects
Some products available contain chilli as well as garlic and pyrethrins. These products claim to kill, deter and irritate insects. Spray on aphids, ants and caterpillars.
Take care when using this product as chilli is a serious irritant to the skin and especially to the eyes. After peeling off your gloves, wash your hands well.
Bordeaux spray for fungal diseases
Bordeaux spray is a mixture of copper sulphate and lime. This is effective on leaf curl and brown rot on stone-fruit trees. There are a number of products commercially available for the home gardener.
Follow label instruction during application as this mixture may irritate eyes and skin. As it will burn the foliage of plants, only apply chemical in autumn at leaf-drop and again in late winter while trees are still bare.
Molasses spray for chewing insects
Caterpillars and other chewing insects apparently dislike the taste of leaves treated with this spray. Dissolve one tablespoon of molasses in one litre of warm water and add a teaspoon of liquid soap. Spray both upper and lower surfaces of the leaves.
Some gardeners claim that by doubling the amount of molasses and applying the solution to the soil, they have achieved a degree of success against root knot nematodes.
Oil sprays for sap-sucking insects
These work by suffocating mites, scales and other soft-bodied sap-suckers. A number of companies sell petroleum oil under the name ‘white oil’ or ‘horticultural oil’ for home gardeners. White oil controls leaf miner, scales, aphids, mealy bugs and mites. Botanical oils, made from plant oils, are also available and work in the same way.