Horticultural soft soap is distinct from household soap, being composed of selected vegetable oils made into soaps. It is applied as a spray to plants as a non-residual, contact insecticide to kill a range of leaf destructive pests, such as aphids. It is important to apply in the right dilution and at the correct time in the pest management strategy.
The content of soft soap
Horticultural soft soap is not household soap, which is toxic to plants. It is closer to saddle soap, but is not soft soap, which is a household soap not usable on plants. It is based on a range of vegetable oils that have been specially converted into horticultural soap. It is necessarily liquid, as it is used for spraying. These oils are highly refined before the soap making process begins.
It is a non-residual, contact insecticide. Residual insecticides are those which leave a trace in the soil, and they concern organic growers greatly, as they may kill beneficial insects that horticulturalists and farmers want and may harm humans. Non-residual insecticides break down quickly, and are thus acceptable in organic cultivation. Horticultural soft soap leaves no toxic by-products. As a contact insecticide, it destroys the insect by damaging it as it contacts the skin. It is normally applied as a spray, but in small gardens it can be applied by sponge.
Its mode of action is to damage the cuticle of the target insects. The chemical effect is to prevent the evacuation of waste products from cells, which then build up in the pest, killing it or damaging it. The application of the soap can cause dehydration in the target pests. The sticky soap can prevent movement and therefore impede breeding. The soap is particularly useful against aphids and other leaf destroying insects. It also attacks white-fly, spider mites, thrips, mealy bugs and scale insects.
Not being toxic to humans and breaks down easily and quickly means that it can be applied any time up to harvesting. However, plants with strong leaves should have it applied in a dilution of 1:30; whereas plants with softer leaves, such as peppers, need 1:50. Some plants, such as fuchsias and ferns are damaged by it. It should not be applied to bedding plants in flower.
If you are applying it as part of an integrated pest management program, leave a significant gap before and/or after introducing biological predators. In these programs, chemical, cultural and biological means are integrated to create maximum pest control effect. However, if you apply it when the biological insect predators are operative, you might kill them too.