A very handy “tool” when growing apples is dormant oil spray for apple tree pests. Read on to learn all about it.

The two keys to successful apple growing are pruning and spraying for apple tree pests. Growing apple trees requires the adherence to a spray schedule for insect control and one of the most important sprays is dormant oil. “Dormant,” in this case, refers to the time of application, rather than the type of oil.

What is dormant oil?

Dormant oil is a type of horticultural oil that is composed of “… highly refined petroleum that is filtered and distilled to remove compounds that can harm plants,” according to Martha Barajas with the University of Nevada, Reno Extension. She goes on to state that these oils are  “… 92 percent to 99 percent pure.” 

An emulsifier is then added to help the water mix with the oil, thus making it easier to spray. 

Dormant oil kills pests by suffocation. 

Which apple tree pests does dormant oil control?

Dormant oils control a number of garden pests that overwinter on the apple tree and appear when the weather warms in the spring. The spray has no affect on many diseases but will control apple scab (check out the photo here). Pests susceptible to the spray include:

• Immature scale
• Thrips
• Psyllids
• Woolly apple aphids
• Immature white flies
• Certain insect eggs
• Some caterpillars that overwinter as eggs

Unfortunately, dormant oils don’t control apple maggot, one of the more common and destructive pests of apple trees.  Apply an insecticide that contains Spinosad as the active ingredient to control that one.

Spinosad, by the way, is natural. Created by a soil bacterium it is toxic to certain pests. 

When to apply dormant oil spray for apples?

‭Spray dormant oil on the apple tree in early spring (late March or early April) before bud break. Wait until temperatures rise above freezing but don’t wait so long that temperatures are over 80 degrees.

“Dormant oils applied in February or early March are not effective as insects are not actively respiring at this time and, therefore, are not vulnerable to the oil’s suffocating effects,” cautions the experts at Iowa State University Extension. They go on to remind apple growers that “Dormant oil sprays should be applied as close to bud break as possible.”

Apply the oil when the weather is dry and wait if rain is in the forecast.

‭How to apply dormant oil to an apple tree

A hose-end sprayer is the ideal tool to use to apply dormant oil to your apple tree. You can also use a pump sprayer but remember that all of the branches, the leaves (both sides) and the trunk need to be covered. The hose-end sprayer will allow for an easier job.

Follow the label instructions carefully and ensure that the product you use is safe for your apple tree. This should be listed on the product’s label.

Warning

Not all dormant oils are organic pesticides. If you’re growing apples organically, look for oils that carry an “OMRI” certification seal on the label. 

‭Mention of a pesticide is for educational purposes only. Always follow the pesticide label directions. Ensure that you wait the required number of days between pesticide application and when you can harvest your crop (that information is on the label).

‭Photo: Muffet/Creative Commons