Does it pay to spray oil on trees?

Oil sprays, often called Dormant Oil or Horticulture Oil sprays, have been used for years for insect control on trees. But is it really effective and worth it?

The truth is Oil sprays really do work to control a wide range of insects such as Cottony Maple Scale, Honey Locust mites and European Red Mites that overwinter on trees. The Oil can kill exposed mites and insects by covering their breathing tube called a spiracle or by penetrating the external cuticle which leads to the internal cells failing. Essentially the oil is suffocating the egg or insect.

Armed with this knowledge, many home owners purchase a small bottle from the local farm or garden store, mix in a gallon can and spray their tree. This same home owner will then say it doesn’t work. Well a couple of things to keep in mind.

It is not one hundred percent effective because some insects stack their eggs on top of each other so the oil cannot penetrate to the lower layer. And if the insect is not exposed it will not harm them. The oil often is not able to get into the area they are harboring in. Insects that fly in at a later time, will not be affected. There are limitations with any insect control application due to environment and habitat.

The second issue is the application. A professional applicator is trained to use the right product at the right time. The label of every pesticide is a legal document that must be strictly followed. Not all Oils are created equal. The term Dormant Oil can refer to a lesser refined oil. Most Horticulture Oils are refined from petroleum oil. And there are a few Oils made from cottonseed oil. The key to the refinement is commercial level sprays have an emulsifier to help the oil mix with water. Water is what is termed the carrier. Many oils are mixed 1 gallon of oil to 100 gallons of water or carrier. Oil and water do not mix well and if a plant is coated with too much oil, it can actually become toxic to the plant. The common label will state the tree must be sprayed to run-off. Remember the insects must have a thorough contact so the oil can suffocate them. This means a lot must be sprayed to coat everything. A gallon of mixed product is not going to do the job. To be effective in a yard with a lot of trees it is necessary to use equipment that can spray hundreds of gallons, thirty to forty feet high.

So, is it worth having Horticulture Oil sprayed on your trees? The answer is definitely, yes. Most Professional Applicators spray an OMNI Organic rated Oil. This is because the type of treatment done at the right time is less likely to harm beneficial insects. It is not a pesticide using a chemical that can harm the environment. Even if the application achieves a fifty percent effectiveness; that was done without harming the environment. That alone makes it worth it. Keep in mind the goal is not to eradicate all pests, but to limit damage to a level that protects your trees from harm.

In conclusion, like any application to control insects, it is important to know how to use the product to get the most effective results. Horticulture Oil is one tool to accomplish insect control, and it works very well with the least amount of harm to the environment.