Fruit Tree Spray for Shrubs

Horticultural oil spray helps control harmful insects on azalea bushes.

Horticultural oil is used for disease and insect control on fruit trees and shrubs. It is also known as dormant oil spray, summer spray and light petroleum spray. Cottonseed oil, vegetable oil and neem seed oil are also used as insect spray on shrubs. Fruit trees are sprayed during their dormant season and in spring; shrubs are sprayed when insect damage is noticed.

Shrub Pests

Aphids, borers, scarab beetles, spider mites and leaf-chewing caterpillars are insects that damage shrubs and also infect fruit trees. Aphids inhabit the underside of leaves and stems, congregating in colonies. They are sucking insects that remove life-giving moisture from all types of shrubs. Apply dormant oil spray in early spring when aphids feed on new plant growth. Azalea lace bugs may also be eradicated with horticultural oil spray.

Types of Oil Sprays

Summer oil and dormant oil are lightweight petroleum oil sprays that smother insects or interfere with their metabolism. Mineral oil is also used as a spray. Neem seed oil and cottonseed oil are vegetable alternatives to petroleum-based products. The chemical compound azadirachtin in neem seed oil eradicates fungi and harmful insect pests. Soybean, canola and cottonseed oil are effective insecticidal sprays for borers. Oil sprays used to eradicate viruses on shrubs are called "stylet oils."

Integrated Pest Management Techniques

Home gardeners and landscape managers are encouraged to use the Integrated Pest Management (IPM) approach to eradicating shrub pests and disease, according to the University of Minnesota Extension website. Choose the least toxic method first and use toxic synthetic chemical pesticide sprays only as a last resort. Horticultural spray is not toxic to people, pets, vegetation or beneficial insects.

Beneficial Insects

Beneficial insects such as lacewings, lady beetles, pirate bugs, praying mantids and robber flies feed on harmful shrub pests. Horticultural oil spray has little effect on these beneficials. Lacewings feed on aphids; robber flies and stink bugs attack grasshoppers; and parasitic wasps eat scale, whiteflies and leafminers. Other beneficial insects that help keep shrubs healthy are big-eyed bugs, spiders and assassin bugs.

References

• Colorado State University Extension; Insect Control: Horticultural Oils; Cranshaw et al.
• University of Minnesota Extension; Insecticide Suggestions to Manage Landscape Tree & Shrub Insects; Vera Krischik et al.; 2003
• University of California at Davis; the California Backyard Orchard; Pests & Diseases
• University of Florida Extension; Entomology & Nemotology; Beneficial Insects Sheet 2; D.E. Short et al.

Resources

• Clemson University Extension; Less Toxic Insecticides; Karen Russ, August 2005