Neem oil might be your best pesticide

Monday, April 30, 2018 2:57 PM

Two weeks ago, I wrote about using horticultural oils to control pests in your yard and garden, but one deserves a column of its own.

If you’ve been searching for a safe and nontoxic pesticide, neem oil might be the product for you. Neem offers just about everything a gardener would want with none of the nasty effects of many man-made preparations may contain.

Neem oil is a pesticide that occurs naturally from seeds in the neem tree, or Azadirachta indica. The tree is found in South Asia and India, where it is an ornamental shade tree.

It has a bitter taste, garlicy smell, and has been used for hundreds of years to control plant diseases and pests. Its seeds also have been used in wax, oil, soap, organic cosmetics, toothpaste and pet shampoo.

Although the oil can be found in most of the tree, the seeds hold the highest concentration. The oil contains a mixture of components with azadirachtin being the most effective for use as a pesticide. Neem can be found in granular form, as a dust, a wettable powder or a concentrate.

It works as a repellent and has insecticidal properties that interrupt insects’ hormonal system, making it difficult for them to lay eggs or grow well. It also interferes with their ability to feed and mate, thereby weakening the population as a whole. As an oil, it works by smothering the insects.

One of the best things about this pesticide is that it’s very safe if applied according to label directions. It has a half-life of three to 22 days when used as a drench in soil, but only 45 minutes to four days when mixed with water. It is virtually nontoxic to birds, bees and wildlife, making it one of the safest controls you can use in your yard. It can control aphids, mealybugs, thrips, whiteflies, scale and most insects with soft bodies.

When mixed with water and applied as a foliar spray, it works just like other horticultural oils do, by smothering the breathing holes of the insects. Since some plants can be affected by neem oil, be sure to mix up a small amount and test on a small area of the plant first. Wait 24 hours and make sure there is no damage before applying the rest.

Apply neem in the evening or on a cloudy day when there is no direct light to avoid having the foliage burn and to allow time for the oil to seep into the plant. Do not use neem in extreme hot or cold temperatures and avoid using it on plants that are stressed.

Weekly applications will kill pests and keep things like powdery mildew in check. Apply according to label directions and coat the leaves.

Neem is also safe around bees – although I wouldn’t advise spraying it directly on the bees or their hives. And since it does not target insects that do not chew on leaves, beneficial insects like butterflies and ladybugs won’t be harmed. However, the aphids that you want to kill are the food supply for your ladybugs, so if you use neem to kill aphids, your ladybugs may disappear too.

Although the perfect insecticide doesn’t exist, neem is close. It controls pests without harming our food supply.

Gail Vanik can be reached at 970-565-8274 or by email at