All About Dormant Oil

Bradford Greenhouses Blog

Dormant oil is a combination of horticulture oil and lime sulphur that when sprayed on dormant plants, kills and protects them from many damaging insect and fungal problems. It is especially useful on fruit trees.

What are the benefits?

This spray can be used on fruit trees, roses and many deciduous ornamentals. It is especially useful in killing off overwintering insects and fungal disease. By killing these pests before they get a chance to become a big problem this growing season, you’ll help your plants out immensely.

Source: http://utahpests.usu.edu/

Aphid eggs on a dormant fruit tree bud. (Source: http://utahpests.usu.edu/)

The oil will help control overwintering insects such as: blister and rust mites, red mite eggs, aphid eggs, scale insects, twig borer, plum black knot, peach leaf curl, as well as overwintering fungal diseases.

Some plants are however sensitive to this oil, so it is best not to use it on: Colorado blue spruce, butternut, Japanese maple, sugar maple, beech, hickory, holly, walnut, or Douglas fir.

When to spray

Now is the time to apply your fruit trees with dormant oil. For most trees, this application should be done before the buds break open, as application after bud break can damage leaves. Usually February through early April is a good time to apply.

Source: http://www.appleman.ca/

These buds are dormant; it is safe to spray this tree. (Source: http://www.appleman.ca/)

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These buds have broken and begun to leaf out; it is too late to apply dormant oil to this tree.

You’ll want to apply it on a day that is 0 degrees Celsius or above (so that the oil can dry and not freeze). Apply it early in the morning so the oil has a chance to dry during the course of the day. It is also important that there is no precipitation for at least 24 hours after application, you don’t want your oil to be washed away before it dries!

A day with low wind is better, higher winds mean less of the spray will adhere to the trees.

Once the plants have broken dormancy; some species can tolerate applications of horticultural oil (but not the mixture of horticulture oil and lime sulphur). Always follow the instructions on the product packaging. If you have a plant and you are unsure if it can tolerate the oil, spray some on a test leaf. If the plant cannot withstand the oil, leaf damage will show in 24 hours. If the test leaf is damaged, do not spray the entire plant.

How to spray

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Mix the lime sulphur and horticulture oil according to package directions. We have it available for sale as a kit. You’ll also need some means of spraying the mixture. A handheld mister bottle or pump sprayer is useful for small applications. A large tank sprayer, or a dormant spray applicator that attaches to your garden hose are better for larger jobs.

Regardless of what applicator you’re using, start spraying at the top of the plant. Continue spraying until the oil just begins to drip off the branches. Move downward until your plant is coated with oil.

For roses, spraying the soil around the base of the plant can be helpful in controlling powdery mildew and black spot.

Safety Precautions
  • Always read and follow the instructions on the product label.
  • Mix only what you can use; the mixture of horticulture oil and lime sulphur cannot be stored for later use.
  • For spraying any pesticide, wear protective clothing. Wearing a long sleeved shirt, hat, chemical resistant gloves and goggles would be ideal.
  • Wash hands and face after application.
  • It’s important to note that the lime sulphur can permanently stain wood, stone, pavement etc. If you are spraying in close proximity to one of these surfaces, be sure not to get it on any on them. Laying down a plastic sheet to prevent splash/spray can also be beneficial.