Holly: Green algae

categories: Holly Holly Diseases Ornamentals Shrubs

revision date: 2022-12-05 12:00

Green algae on holly.
Green algae on holly
Photo by: B.M. Johnson


Green algae grows on the surface only of leaves, twigs, and trunks. Wet, humid weather favors development of these microscopic, moisture-loving, primitive plants. The colonized holly is not harmed unless sufficient algal growth develops on the leaves and interferes with the photosynthetic process. Algal growth can cause plants to appear somewhat dirty or unhealthy. Typically, however, algae is only an aesthetic concern.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

  • Space plantings and prune to provide good air circulation and reduce humidity.
  • Avoid overhead watering or limit it to times when foliage can dry quickly.
  • Do not plant in very damp areas or densely shaded sites.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

  • Use as preventative treatments.
  • Do not apply sulfur products after April 1 or on a warm day, or defoliation may occur.
  • Do not apply sulfur products within 2-4 weeks of a horticultural oil application.
  • Homeowners should not make foliar applications to trees over 10 ft tall.
  • Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Approved Pesticides

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.