First I must disclose that I am a strong opponent of using synthetic chemicals in the yard and garden. But when bugs start munching and fungus start rotting your plants, action must be taken to correct the situation. One of the most ecologically friendly solutions available is Neem oil.
Neem oil is a vegetable oil cold-pressed from the fruits and seeds of the Azadirachta indica tree. This tree is native to the Indian sub-continent and has been introduced to many areas of the sub-tropics and tropics where it is recognized as an important commercial crop for production of a wide range of agricultural and medicinal products. The Azadirachta indica tree will grow in sub-tropical Florida, but finding specimens for purchase may be difficult. If you are interested in purchasing a Neem tree, visit Top Tropicals, add your e-mail address to their “Waiting List” and they will contact you by e-mail when plants become available.
The Neem tree has been revered for thousands of years by the people of India for its numerous therapeutic properties. While it is beyond the scope of this article to elaborate upon the pharmaceutical uses of the Neem tree, I will mention that it has been used for preparing cosmetics (such as soap, hair care products, body lotions and skin care creams) as well as medicines for the treatment of skin diseases, inflammation, fever, rheumatic disorders, periodontal diseases, earache, headache, fever, sore throat and many other ailments. However, Neem oil is not used as cooking oil.
Within the scope of this article Neem oil finds wide usage as a bio-pesticide for organic farming as it repels a wide variety of pests including aphids, beetles, caterpillars, flies, fungi (anthracnose, black spot, powdery mildew, and rusts), gnats, leaf miners, locusts, mealy bugs, mites, nematodes and more. Meanwhile, neem oil is not known to be harmful to some beneficial insects (such as butterflies, honeybees and lady bugs – as long as they are not sprayed directly), birds, fish, humans, and mammals.
Neem oil contains numerous compounds, metabolites, steroids and triterpenoids which interfere with the normal life cycle of certain insects including their feeding, molting, mating, and egg laying. Neem oil kills some pests (after they've eaten plant material sprayed with it), while it repels others with its strong smell (an odor smelling like a mixture of garlic, peanut and orange).
The active compounds in Neem oil are very similar to the natural hormones found in insects. The presence of Neem oil active compounds block the functioning of the real hormones in certain insects. This causes a cascade of effects in the insects leading them to stop eating, molting, mating, and laying eggs. But for the effects to take place the insects must first ingest the Neem oil either by eating plant material that has been sprayed with it or by respiring the oil. The reason Neem oil does not effect most beneficial insects is because they do not eat the oil sprayed on plants. But at the same time, if the beneficial insects are directly sprayed with Neem oil, they may breath it into their systems which is why you should avoid spraying beneficial insects with Neem oil.
Given the explanation of how Neem oil is thought to work above, please understand that it does not kill instantly; it will need some time to work. Wait at least a week before judging its effectiveness. Also, if it rains shortly after application you may need to spray again. Apply Neem oil every 7 days to curtail an infestation or every other week for infestation prevention.
Neem oil is available at most garden centers. Please be certain to follow all directions for application.
Additional information regarding Neem: EPA Fact Sheet; Organic Materials Review Institute; Neem Oil and Neem tree