Can’t tell by the weather today (not another snow storm!), but we are entering the window for our last opportunities to make dormant treatments of insecticidal oils.
Insecticidal or horticultural oils are broad-spectrum insecticides and miticides effective against many soft-bodied insects and mites and their eggs. Oils kill insects by altering their cell membrane functions and blocking the exchange of gasses. They may also deter feeding and oviposition (egg laying) and might even repel certain insects away from treated plants. Dormant treatments are generally made in the landscape at 2 to- 4% solutions in late winter and early spring (now).
Phytotoxicity to spruce from insecticidal oil application. Photo: Sabrina Tirpak, Rutgers PDL
Each year the Plant Diagnostic Lab gets samples of plants, mostly conifers, burned by dormant oil treatments. Here are a couple things to keep in mind, so you don’t wind up with an insecticidal oil inferno:
Do not exceed the label rate.
Keep the spray agitated during application.
Do not tank mix with fungicides and herbicides.
Do not apply with or within 30 days of any pesticide that contains sulfur.
Do not apply to plants under drought stress.
Oil will remove the waxy bloom from some varieties of plants.
Avoid spraying during periods of overcast skies and high humidity.
Click here for some more information on using oils in the landscape.
