Holly: Green algae
Photo by: B.M. Johnson
Biology
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
See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.
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: Always read and follow label directions when working with pesticides.
For more information on using pesticides visit :
- 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
If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.
WSU Extension programs and employment are available to all without discrimination.
Evidence of noncompliance may be reported through your local Extension office.