Controlling Fruit Tree and Landscape Pests with Horticultural Oils

Fruit tree oil applications are commonly recommended as either a dormant or delayed dormant application. Dormant oil applications darken tree bark and buds, speeding up spring bud development. This reduces the flower buds ability to withstand cold temperatures, therefore, applications are best delayed until just before bud break.

• Dormant application- A dormant application is made just before bud break and is targeted to control Eriophyid mites, San Jose and oystershell scale.
• Delayed dormant application- A delayed-dormant application is made when plants are in the green tip (fruit buds are open at tip showing 1/16 inch of green) through half-inch green bud growth stage (1/2 inch of leaf tissue is projecting from the fruit buds) for fruit trees to control insects such as San Jose scale, European red mite eggs, and aphid eggs. Many labels will recommend higher rates of oil be used for a dormant application and slightly lower rates for a delayed-dormant application, however, always follow label directions and rate information when mixing oil products.
• Dormant and delayed-Dormant oil applications are most effective when applied with large quantities of water, which is necessary to thoroughly cover all the bark cracks and crevices for mite and scale control. Also make sure branches in the center of the tree receive adequate coverage. Poorly pruned trees with heavy center branching will required higher amounts of water for thorough coverage. Based on tree height, a 20 feet tall tree should be sprayed using a minimum of 4 gallons of water; tree height 15 feet, 3 gallons; tree height 10 feet, 2 gallons; and tree height 5 feet, 1 gallon.

Later season fruit tree applications usually are made using an orchard spray, which incorporates both a fungicide and insecticide for control of both disease and insect problems.

Insects such as adelgids, aphids, leafhoppers, scale insects, mites and whiteflies can be controlled on landscape ornamentals with oil applications.

• Aphids- many hosts. Spray affected plants during the growing season when mites are detected.
• Oystershell scale- many hosts. Spray affected plants after eggs hatch and light yellow crawlers appear (late May). Repeat in 7-10 days, unless prohibited by the label. Oil may damage some maples.
• Pine needle scale- hosts include pine and spruce trees. Thoroughly spray foliage, branches and trunk with horticultural oil in March.
• Spruce spider mite- hosts include spruce, juniper and pine. Spray affected trees during the dormant season just before bud break. (April) Repeat applications when mites are detected during the growing season (April to May, and September to October). Make the first application then a second application 7-10 days later. Oil will remove the blue needle color of spruce.
• Two spotted spider mite- many hosts. Spray affected trees during the growing season when mites are detected. Make the first application then a second application 7-10 days later. Oil will remove the blue needle color of spruce.
• Whiteflies- many hosts. Only nymphs are killed and thorough coverage of the undersides of leaves is necessary for control. Spray affected trees during the growing season when whiteflies are detected. Repeat applications as needed and according to label directions.

Next week- Tips on making a horticultural oil application most effective.

Sarah Browning is a Horticulture Extension Educator with University of Nebraska- Lincoln Extension in Dodge and Saunders Counties. She can be contacted by phone at 727-2775: by mail at 1206 W. 23rd Street, Fremont, NE 68025: or by e-mail at sbrowning2@unl.edu