Dormant Oil and Lime Sulfur Spray

Used on trees, shrubs and roses, dormant oil and lime sulfter spray smother any insects and prevent the hatching of eggs that have over wintered in your plants.

Rose Collection
Item # 99522 		Cold Hardy Shrub Rose Collection

Sampler $36.96
  • Topic: Pests
  • Keywords: spray, insects, pests, Products
  • Date: March 2002

© All articles are copyrighted by High Country Gardens. Republication is prohibited without Permission.

Now is a great time to use two products that prevent hours of headaches in the future: dormant oil and lime sulfur spray. Used on trees, shrubs and roses, both products smother any insects and prevent the hatching of eggs that have over wintered in your plants; lime sulfur spray is also generally used as an effective fungicide. If you plan on using both products, start with the sulfur spray. Follow the directions on the bottle closely, and be thorough in your application. Wait two weeks before applying the dormant oil.

Specifics: There are horticultural oils that are suitable for spraying after your trees have come out of dormancy, but they must be a thinner consistency to avoid magnifying sun rays (and burning plants) and smothering the plants themselves. Take advantage of this time of year and use the thicker dormant oil—it’s more effective.

If you spray dormant oil after the first buds start to form, the oil can burn new growth. If you see burned leaves as a result of the application, you may have either applied too much or sprayed when the buds were too far developed. Next year you’ll know better. Always read directions!

Some gardeners suggest waiting until you have 24 hours to 4 days of above freezing temperatures, but this is impractical in our climate—if you wait too long the plants will no longer be dormant! Try to coincide your spraying with warmer daytime temperatures so that the oil can flow freely and coat thoroughly, and avoid spraying when severe frosts are forecasted. Evergreen trees can be more susceptible to oil damage, so mixing at the lowest recommended rate and aiming for +40 degree temperatures is a good idea.

Dormant oil spray controls a wide range of pests, including aphids, whiteflies, scale, mites, mealy bug and some caterpillars. It will suffocate adults and smother eggs. In order for the spray to be effective you must cover the insects with the oil. If you don’t pay attention to cracks or the underside of leaves you will be missing the favorite hiding places of many pests. Some statistics suggest that dormant oil kills 80% of insect eggs laid during the previous fall.

It’s important to know that petroleum oil is phytotoxic to some ornamentals. The spray can damage maple, black walnut and redbud trees, and it can remove the blue growth on Colorado blue spruce. Always read the labels of any product before applying it to your trees.

Lime Sulfur Spray is one of the safest fungicides, and also works to control insects. It can be used to control peach leaf curl, brown rot, leaf spot, powdery mildew, rust, black spot and blight, as well as mites, scale, borers and aphids.

The important temperature to consider with sulfur spray is how warm it will be—never spray when the temperature could rise above 80 degrees.

Most manufacturers do not recommend the use of sulfur spray on evergreens, euonymus or rhododendrons.

Do not apply these products simultaneously. Directions indicate that it is necessary to wait at least two weeks after applying sulfur spray before using a horticultural oil.