How to Treat Scale on Shrubs

Overview

Scale insects are sap-suckers. They dine upon the foliage, fruits or stems of your shrubs. Diets vary according to the assailant's species. Damage inflicted upon a plant by scales can eventually cause part or all of the victim to wither and die. Adults are difficult to control due to body coverings that protect them from contact pesticides. Scale larvae, however, go through vulnerable stages of development. Initiate a good management regime for effective control of scales. Work around the life schedules of insect allies present in your area to utilize their services rather than eradicating the good with the bad. Exercise healthy plant maintenance and incorporate natural controls into your pest management efforts before spraying your shrubs with toxins.

Step 1

Apply strips of double-sided tape on the limbs of affected plants to trap scale insects. Inspect shrubs carefully each day. Hand-pick and squash any bugs or larvae that you find. If you don't care for squashing, drop the little beasties into a bucket of soapy water.

Step 2

Spread a plastic garbage bag out beneath the infested plant. Shake the stems and branches to dislodge scales. Pick them up and squash them when they fall onto the garbage bag.

Step 3

Treat scales with horticultural oil in March or April before your plants set buds. Mix with water to form a 2-to-4 percent solution. The concentration will depend upon the species of the plant and composition variations between individual products. Spray in temperatures above 32 degrees F. Coat all leaf and stem surfaces thoroughly. Follow manufacturer's recommendations carefully.

Step 4

Spray crawlers on affected plants with insecticidal soap as needed. These products are effective only for scales still in their soft-bodied forms.

Tips and Warnings

  • Horticultural oil asphyxiates over-wintering nymphs as well as scales in other development stages; horticultural oil and insecticidal soaps kill insect predator allies as indiscriminately as they kill scales. Follow manufacturer's instructions carefully.

Things You'll Need

  • Double-sided tape
  • Plastic garbage bags
  • Bucket
  • Soap

References

  • Iowa State University of Science and Technology: Scale Insects on Ornamental Plants
  • University of Minnesota: Scale Insects of Trees and Shrubs
  • University of Rhode Island: Scale Insects, Factsheets
  • University of California: Using Horticultural Oil Sprays
  • University of Washington Bontanic Gardens: Horticultural Oil

Who Can Help

  • North Carolina State University: Cottony Scales on Shrubs and Trees
Keywords: scales, scale insects, how to treat scale on shrubs

About this Author

Axl J. Amistaadt began as a part-time amateur freelance writer in 1985, turned professional in 2005, and became a full-time writer in 2007. Amistaadt’s major focus is publishing material for GardenGuides. Areas of expertise include home gardening, horticulture, alternative and home remedies, pets, wildlife, handcrafts, cooking, and juvenile science experiments.