WSU Extension


Lawn and Turf : Algae
(revision date: 4/18/2018)

Algae are tiny, single-celled plants commonly found in lakes and wet areas. Algal growth on lawns is common in the coastal regions of the Pacific Northwest, particularly on grass planted in wet, low-lying, or shaded areas. Also at risk are lawns with compacted soils that prevent proper drainage. Algae form a slick greenish to black scum on the surface of the soil, particularly over thin turfgrass. It can look like an oil spot. The grass is usually not killed, but growth is reduced because of shading and reduced air and light penetration. The algal scum becomes a black, water-repellent crust in dry conditions.
Management Options

Non-Chemical Management
  • Improve soil drainage.
  • Soil aeration and thatch removal may be useful.
  • Improve light penetration in shady areas by thinning shrubs and trees.
  • Maintain a healthy, vigorous lawn by providing proper culture including proper irrigation and fertilization.
  • Avoid excessive use of nitrogen fertilizer.
Select non-chemical management options as your first choice!

Chemical Management

These give only temporary control. Identify and correct the causes of turf deterioration for more lasting results.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • Monterey Liqui-Cop Copper Fungicidal Garden Spray
    Active ingredient: copper-ammonia complex  |  EPA reg no: 54705-7
  • This list may not include all products registered for this use.
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Caption: Black algae
Photo by: G. Stahnke