How To Fix Fungus and Pests On Trees

Tree Care Tips By Louisville Kentucky Arborist

Dormant oil, sprayed in late winter, early spring, or sprayed in the summer, is a safe and effective tool in helping to control pests and some fungal diseases. 

First introduced as a way of controlling damaging insects on fruit trees, oils were nontoxic and did not harm future fruit. Sprayed in late winter, just before bud break, these heavy oils helped to eliminate many such overwintering and spring emerging pests as spider mites, scale, mealybugs, thrips, whiteflies, caterpillars, and aphids.

The modern-day dormant oil is much lighter in composition and therefore can be sprayed on most plants throughout the season without detrimental effect. It remains very effective against powdery mildew, which tends to appear in mid to late summer on our roses, hawthorns, dogwoods, and lilacs.

The oil sprays are ecologically safe to use, too, as they have no harmful effects on animals or people. Any excess oil does not linger; it evaporates quickly and does not leave a residue.

Many of the oils are made up of a type of mineral oil, with an emulsifying agent added so the oil will mix with water. This combination enables the spray to coat the plant, which effectively smothers the insects and insect eggs.

Some of our shrubs and trees, such as boxwoods, azaleas, arborvitae, spruce, and pines, are highly susceptible to leaf damaging insects. And the scale insect can be damaging to our magnolias, oaks, and young tulip poplars. 

An eco-friendly product, Dormant Oil is sprayed prior to honeybee and bumblebee activity. 

Spraying with Dormant Oil in late winter and early spring can help to protect our landscape plants and eliminate a large portion of the damaging insects from our beds. Dormant Oil sprays are an effective and ecologically sound and safe tool to have in the PHC toolbox.