Horticultural oil works by suffocating the eggs of the insects before they become a problem. Making your own oil at home is an alternative to other shop-bought pesticides that can harm children, pets and other animals. In order to make the oil into an easy-to-apply spray, mix the oil with water by adding an emulsifying agent.
Mix 15 ml (1 tbsp) of liquid soap with 250 ml (1 cup) of cottonseed oil. You can also use safflower oil, soybean oil or vegetable oil as an alternative to cottonseed oil.
Mix 22 ml (1 1/2 tbsp) of your oil mixture for every 250 ml (1 cup) of water. Using a spray bottle for your horticultural oil will make the application process simple.
Shake mixture well and apply to infected plants. Apply your horticultural oil in dormant months to the branches, leaves and roots of the plant. This will help control the insects before the warm summer season. You can also apply the oil during the spring and summer months to reduce insects by controlling other stages in the insects' lives.
Do not apply your homemade horticultural oil if temperatures are above 29 degrees C (85F).
Do not apply oil to plants or trees that are not healthy because of drought or excessive heat.