The neem tree has been used for centuries in India for its many benefits to people and plants. The fresh flowers, leaves, bark and twigs all have been used for food and medicine, but the most important part of the plant for both the gardener and the home herbalist is the seed.
Neem oil extracted from the neem seed is a natural pesticide, which is used for fungal diseases including powdery mildew and rust, mites, and a wide range of insects such as aphids, whiteflies, beetles, and leaf rollers.
Numerous components in the oil have been identified as having pesticidal properties, but the primary effect is from azadirachtin. When applied as a foliar spray, neem oil has been found to repel insects and nematodes, reduce their feeding ability, and interfere with insect growth and ability to lay eggs.
Although it will repel some insects from eating your vegetables in the first place, the insects must eat the neem oil in order for them to be harmed by it. Thus it is not considered dangerous to bees and other pollinators.
Neem oil is rapidly broken down in the environment, and it must be reapplied every 3 to 5 days to maintain its effectiveness.
Neem Meal and Neem Cake
Once the oil is pressed out of the seeds, the left over pulp is dried and used as neem seed meal and neem cake. Neem meal is an excellent fertilizer that is high in nitrogen. Some studies have shown that it also stimulates microbial activity in the soil. Neem cake also contains allelochemicals such as nimbidin and thionemone, which have some pesticidal properties.
Neem for People
Neem oil has been used for centuries in Ayurvedic medicine. It is found in many products today, including toothpaste, cosmetics, soaps and shampoos. It has been used for skin problems such as athletes foot, acne, nail fungus, poison oak, skin infections, rashes, yeast infections, insect bites, eczema, and warts. It also has been used as an insect repellant.
Some pet shampoos and bug repellants also contain neem, however it is important to always consult your veterinarian before using neem on your pets. Some cats have been found to have a dangerous reaction to the oil.
There have been numerous studies conducted regarding the safety of neem oil, and no adverse effects have been observed in people with long term exposure to neem. Some people experience skin irritation from short term exposure.
To see if neem is a good solution for whatever is bugging you, check out the UCDavis IPM website or contact your local agricultural extension agency.
Photo courtesy of William M. Ciesla, Forest Health Management International, Bugwood.org