Dilute with water (1:50) and apply by sprayer.
- Soft soaps have been used to control insects for more than 200 years.
- Soft soap consists of salts of potassium fatty acids and is biodegradable. It is readily broken down by bacteria and therefore not considered a pollutant.
- Soaps are different from synthetic detergents, which are made from petroleum oil.
The mechanism by which soap kills insects is in fact not well understood. It appears that soap washes away the insect's cuticle, and then blocks its spiracles preventing oxygen transfer. In other words, the soap washes off the insect's protective waxy covering, and stops it breathing.
Although soap is more commonly known for its ability to kill insect pests on plants, there are many uses for it against pests in animal houses, and on animals themselves, even humans. Soap has also been shown to have an effect on fungi. The mechanism is thought to be very similar: the soap causes the fungal cells to shrink preventing oxygen diffusion.
A Soft soap can kill insects, provided enough soap covers enough of the insect.
- It may also be useful against plant fungal diseases (at reduced rates).
- It can be used in a way to minimise effects on beneficial insects.
- Risk of spray scorch is much reduced in the absence of alcohol and detergents.
- It is regarded as environmentally safe, and is fully biodegradable.
- It is not persistent – an environmental and consumer benefit.
- Can be a useful water softener (and hand cleaner).
- Crop residues do not appear to be an issue.
Limitations of natural soft soap
- Soft soap is contact action only: there is no persistence of activity on the leaf.
- Repeat applications are usually necessary.
- Pests vary in their sensitivity.
- Increased rates may be required where hard water is used for spraying (some of the soap will be used in precipitating an insoluble scum).
Soft soap cannot be readily mixed with other chemicals and fertilisers, (it is likely to affect the performance of other chemicals mixed with it, and the addition of some chemicals can alter the structure of the soft soap itself).