Dormant Spraying

August 31, 2021

Dormant Spraying

Dormant spraying combines horticulture oil and lime sulphur to kill overwintering insects (such as scale and mites), insect eggs, and diseases on certain hardy landscape plants.

WHICH PLANTS BENEFIT FROM A DORMANT SPRAY APPLICATION?

Dormant oil and lime sulphur are best applied to fruit trees, roses, ornamental shrubs (highbush cranberry and European snowball), evergreens (cedars, green junipers, and euonymus), and trees (hawthorn, crab apple, and honey locust).
Do not use a dormant spray on beech, butternut, Colorado blue spruce, hickory, holly, sugar maple, Japanese maple, or walnut.

WHEN TO SPRAY

This combination spray can only be applied when plants are completely dormant.
Applying at the improper time can burn leaf buds that have started to swell or show any sign of green.
Apply between February and March when the temperature remains at 5°C (41°F) or above for a minimum of 24 hours.
Distribution of the spray will be more efficient on a day without wind; higher wind speeds won’t allow for the mixture to adhere to the plant.
Dormant spray will coat and dry most effectively when the forecast is clear of precipitation.
Spray early in the morning so the plant will be completely dry by evening. Do not spray if there is any chance of frost overnight.

HOW TO SPRAY

Mix lime sulphur and horticulture oil (available together as a dormant spray kit) according to the package directions. The easiest method of application is to use a hose end that attaches to your garden hose.
Spray the plant starting at the top until it just starts to drip off the branches. If you start spraying from the bottom, you will run out of product before the job’s done.
For roses, be sure to spray the soil around the base of the plant as well to control powdery mildew and black spot.

SAFETY TIPS

Mix only what you plan on using; do not save solution for later use.
When spraying any garden pesticide, wear protective clothing, long sleeves, a hat, chemical-resistant gloves, and anti-splash goggles.
Wash hands and face after use.
Do not let any of the mixture fall or drift onto hard surfaces such as interlock, natural stone, brick, concrete, stucco, wood, or aluminum siding as it may leave a permanent stain. If necessary, tape a large piece of plastic to the area before spraying.

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