Dormant Oil and Controlling Borers

Q. We found borers in a large sumac as well as a Chinese pistache ornamental tree. My ash and oak tree have aphids. I want to spray dormant oil but do not have enough information about it. Do I spray only trees without leaves or can I spray evergreen trees like Holly oak and African sumac?

A. Read the label of your Dormant Oil product to make sure your trees are safe to spray but there should be no problem spraying most trees that have leaves. It just requires applying more liquid spray because there is more surface area to cover.

One Dormant Oil available to consumers. There are many out there with different names. Some are called Dormant Oil, some Horticultural Oil, some have their own name for marketing purposes. Read the label.

Dormant oils themselves are not toxic. But using these oils to put a layer or blanket over your plant to "suffocate" bugs and eggs that might survive the winter is important. It’s important to spray the undersides of the leaves because that’s where most of the bugs will be hiding.

Another Dormant Oil in a 2 1/2 gallon container for large jobs. There are many out there. Shop around.

Dormant oils sold to the public are considered "summer oils". That is they are safe to spray even when leaves are present in the spring and fall months. But DONT SPRAY PLANTS WHEN THEY ARE FLOWERING. WITH ANYTHING. Honeybees and other pollinators will be harmed.

FYI. I was curious one year so I sprayed a "dormant oil" (summer oil) in June when I knew air temperatures would get about 105F on about ten different kinds of fruit trees and I was prepared that I might see damage. I sprayed the oil at about 500 am when it was cool. It would get to 105F by about noon. There was no damage.

I am not suggesting that you do this. I was curious what would happen. This is how safe summer oils sold to the consumers are now. Oils can be sprayed after trees have flowered and as new spring leaves have appeared. Good aphid control from a delayed application of "dormant oil" applied in the spring.

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