Greenhouse release of biological control

Organic sprays include the following:

• Mineral and vegetable oils and soaps. These work by smothering, or forming a film on the plant surface on which fungal spores cannot establish. Oils and potassium soaps may also break down the insect cuticle (outer layer).
• Plant based sprays can be made from many products. Garlic, onion, chilli and rhubarb, tomato-leaf and sabadilla are frequently cited examples. They have a repellent effect but may also work directly on soft bodied insects.
• Plant extracts are more precise in their action and generally more effective. They include azadirachtin (from neem), pyrethrum, quassia, ryania and rotenone (or derris). They are often used with natural carriers and synergists such as sesame oil or codacide oil. Beware of these sprays as they may also be toxic to humans and other animals (rotenone is very toxic to fish). Azadirachtin is unique amongst plant based sprays in that it may have some systemic action.
• Diatomaceous earth is an abrasive dust made from the fossilised skeletons of microscopic organisms, It is used as a dry powder or a slurry (for painting on tree bark or the walls of storage buildings). It works by a physical, abrasive action to kill a wide variety of crawling insects. The dry powder is used as a grain protectant and is safe to humans when eaten, but avoid getting in your eyes or nose. Do not use ‘activated’ diatomaceous earth, which is sold for use in swimming pool filters.
• Essential oils are a special class of plant extracts. Citrus and pine oils are readily available in commercial formulations and peppermint oil, tea tree oil and other products have significant potential for development. Combinations of these oils can be used inside kitchen cupboards to deter or kill cockroaches and other pests. Citrus oils and other potent essential oils can burn skin and eyes - use with care.
• Copper, sulphur, alum (aluminium sulphate), iron sulphate, boric acid and other mineral based sprays are also very effective fungicides, molluscicides (snail and slug killers). They are available from any large garden centre or chemical retailer.

A variety of other products including rubbing alcohol (70% isopropyl alcohol) or ammonia for thrips, scale, aphids, whitefly and other small bodied pests. Baking soda (sodium bicarbonate) is a fungicide. Be careful with these products as they may damage leaves on sensitive plants.

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