Rohde’s Organic Dormant Oil Treatment


Dormant oil is a very effective way to help control some of the more troublesome pest and disease problems that attack our most valuable landscape plants. When sprayed thoroughly on the trunks and branches of your deciduous trees and shrubs, it can suffocate overwintering eggs and larvae of insect pests overwintering in the fissures of the bark or nooks and crannies of branches and twigs, waiting for bud break and young shoots to feed on. This helps to prevent early spring infestations, and lessons the numbers of future generations during the spring and summer.

Organic dormant oils are the same lightweight horticultural oils we use in the summer for pest control, and are some of the safest pest control products available. They are safe for people, and the environment. They are designed to evaporate quickly to lessen harm to the plants they are sprayed on, so there is no residue.

Oils don’t cause targeted pests to become resistant as they appear to work in a basic way that is hard for the insects to guard against. The oils suffocate the insects and eggs, and/or interfere with cell membrane functions. They also can interfere with eating and egg laying in some insects.

Insets best controlled are scale, aphids, mites, white fly larva, leaf-rollers, thrips, mealybugs, and most eggs of these and other insects. The oils are also effective on some molds, mildew, and bacterial spores. Tent caterpillar eggs and small larva are also controlled and bacterial fire blight can be lessened.

This is an especially good thing to use on fruit and nut trees and anything in the rose family Rosaceae, such as roses, photinias, indian hawthorns, cotoneaster, pyracantha, quince, etc. It is also helpful on anything that you had a particularly bad case of mold or mildew on, like powdery mildew on Crapemyrtles and black spot on roses.

Dormant oils should not be used on plants that don’t have these problems as it can kill good bugs too.

Some plants are especially sensitive to oils so know or test first. Non-woody plants like herbs, ferns, annuals, evergreens, citrus, orchids, some maples, or in the Euphorbia family like Crown of Thorns and Poinsettia, could be sensitive and can be harmed or killed. Test sprayed for the oil you want to use in a sacrificial spot to see if it turns brown or black if burned. Walnut, and Empire, Mitsu and Red Delicious apple trees may also be sensitive. Read the instructions on the oil you are going to use.

Healthy well hydrated plants are less likely to be harmed by the oils.

The oils should be sprayed anytime from end of January, till the buds begin swelling, usually towards the middle to end of February in North Central Texas, with weather permitting as there needs to be several dry days afterward for evaporation of the oils.

Apply on dry non-humid and non-windy days, above 40 degrees, to insure timely evaporation, and minimize overspray to prevent harming other plants.


Aphid Eggs on buds.


Pear Psylla Eggs on buds.


Mites (little white specks) on buds.