The neem tree (scientifically known as Azadirachta indica) was declared the "Tree of the 21st Century" by the United Nations for its medicinal and environmental benefits. Less commonly known as the Margosa treee, the neem is a revered native of the Indian subcontinent, featuring heavily in the traditional medicines of that region. One of the tree's most concentrated essences--neem oil--is derived from crushing and extracting its ripe seeds. This oil is, among other things, is a potent and widely applicable anti-fungal.
Neem oil has been used as a fungicide for hundreds of years. The wide-leaved neem tree's Sanskrit name was "arishtha" ("reliever of sickness"), and ancient Hindu manuscripts contain chapter after chapter describing the medicinal properties of its fruits, seeds, oil, leaves, roots and bark. Practitioners of Unani and Ayurvedic medicine have used neem oil for centuries for a variety of purposes.
Neem oil effectively controls certain fungi that can inhabit and grow in and on the human body, according to the National Academies Press. Because these fungi have developed a hardiness against synthetic fungicides, they're becoming more and more difficult to control; with neem, they're managed surprisingly easily and without chemical side effects. Neem is effective in treating many different kinds of fungi, including the "athlete's foot" fungus that infects skin and nails, fungus of the intestines, a fungus that attacks the mucous membranes and the yeast-like fungus that causes thrush. Neem oil is used in lotions and tinctures to treat many skin diseases, including scrofula and ulcers, and is even used to eradicate the bacteria that causes leprosy.
Neem oil is an especially effective, safe and environmentally friendly fungicide. In diluted form, It can be sprayed on roses and fruit trees to eradicate powdery mildew, rose rust and black spot. Because it is nontoxic, neem oil is safe to use on vegetable gardens--even on tomatoes and melons, where fungal growth can spread too quickly for synthetic fungicides to be effective. In addition to managing fungus, neem is very effective at smothering insect eggs and soft-bodied pests such as aphids, mites and white flies.
Just like humans, pets are susceptible to fungal infections of the hair, skin, digestive tract, mucus membranes and nails. Neem oil can replace synthetics to address these fungal flare-ups. Fungal infections of the skin (such as mange, Malassezia or Aspergillosis) can be treated with a commercial neem spray or neem dip. Neem oil can be added to regular dog shampoo to help clear up mange or mild cases of ringworm; it is also effective at keeping fleas and ticks at bay. Adding a small amount of neem oil to your pet's food can help to eradicate some intestinal parasites, as well as stimulate liver and immune function to prevent future fungal infections.
There are still limitations on neem's usefulness as a fungicide. Part of the reason it's so environmentally safe is that it's quickly degraded by the environment. Extreme temperatures, exposure to ultraviolet light, mechanical removal by rain or snow and other factors in the environment can remove neem oil from where it was applied or reduce its effectiveness. Therefore, it may be necessary to repeat applications of neem oil more often than with a more dangerous synthetic. In addition, high concentrations of neem oil may cause damage to delicate plants.