Dormant Oil - Timing and Uses

Dormant oils are an effective treatment for pests on plants, particularly during the dormant season. These oils are applied in late fall or early spring, before bud swelling and bud break. This timing is crucial for controlling overwintering insects and insect eggs on fruit trees and woody ornamentals while minimizing risks to plants and beneficial insects.

Using dormant oils can help manage harmful pests and reduce the need for pesticides during the growing season. However, a single treatment may not ensure complete control, so consistent monitoring is essential to prevent further infestations. Dormant oils are effective only when they make direct contact with pests at the correct life stage.

Why Timing Matters 

Applying dormant oil at the right stage in a pest’s life cycle is critical for success. For some pests, the oil works by blocking the spiracles—the air holes they use to breathe. In other cases, it acts as a poison by interacting with fatty acids and disrupting metabolism.

Correct application targets specific pests and their life stages. Avoid indiscriminate spraying, as blanket applications may not be effective and are environmentally irresponsible. As with any pesticide, remember: “A prescription without diagnosis is malpractice.”

Application Guidelines

Avoid using dormant oil in combination with sulfur or sulfur-containing pesticides, as this can cause phytotoxicity, negatively impacting plant health.

Do not apply dormant oil on sensitive plants such as junipers, cedars, Japanese and red maples, smoke trees, and spruce, especially dwarf Alberta spruce.

Apply when temperatures remain above 40°F for at least 24 hours. If applied just before freezing, the oil’s emulsion can break down, causing it to adhere improperly to bark or leaves instead of targeting pests.

Benefits and Considerations

Monitoring trees is vital. Symptoms from pests like autumn mites may only become evident in spring or summer. Fall applications can prevent such damage by suppressing mite adults, immatures, and eggs. The physical mode of action of oils, causing suffocation, requires thorough coverage to be effective.

Various oils are available for garden use, including spray oil and highly refined supreme oil. While older oils were unsuitable for use after dormancy, modern lightweight oils are safer for foliage. These advancements make it easier for gardeners to apply dormant oils with confidence.

Are Earwigs Really That Eerie?

European Earwigs (Forficula auricularia) are common insect pests throughout the United States. They feed on plants, including flowers, garden vegetables, and fruit trees. The common name “Earwig” is based on the false notion that this insect could enter a human ear and cause substantial damage. Earwigs are predominantly reddish brown and adults are typically ¾ of an inch long. The most identifiable feature of the earwig is the appendages at the tail end of the insect which appear to be pinchers or forceps and are referred to as cerci. The male earwig has strongly curved cerci while the female cerci are nearly straight. Earwigs have wings but are rarely seen flying.

Earwig damage to seedling plants, soft fruits, and new flowers can be substantial while damage to mature plants is limited and usually of little concern. Since earwigs are omnivorous, they can be useful as they can feed on aphids and insect eggs. Earwigs are mainly nocturnal creatures that prefer damp and dark locations but can be seen during daylight hours, especially if their hiding places are disturbed. Earwigs often enter homes and other buildings during hot and dry weather or when temperatures drop as in the late fall. Depending upon access points, large numbers of earwigs can invade occupied homes and cause distress for some but they are little more than a nuisance. Earwigs can cause significant damage to certain crops such as stone fruits when they create holes that deeply penetrate fruits. Strawberries, blackberries, and raspberries can also suffer damage although the most substantial damage can occur when earwigs feed on corn silk which will cause pollination problems and poor kernel development. The most typical and obvious damage to plants by earwigs is when they make irregular holes in leaves and flower blossoms.

Controlling or reducing earwig populations can be more than a little challenging. When the goal is to prevent house infestations, residential insecticides, when used according to label instructions, can help. The best method to keep earwigs out is to properly and completely seal around doors and windows with caulk as those are the most prominent entry points. When the goal is to prevent garden or orchard infestation, appropriate insecticide sprays used according to label instructions can suppress the earwig population, especially when conducted soon after dark since earwigs are mostly nocturnal.

Because earwigs beneficially consume other insects, especially aphids, and are a non-dangerous nuisance indoors, it turns out that earwigs aren’t that eerie after all.