Turf Algae Control

Algae forms a green-to-black film or crust over thin turf and exposed soil. It is a symptom of a persistently wet, weak-growing site rather than a disease that invades healthy grass tissue.

What to Look For

Look for a slick green film when wet and a dark, cracked crust when dry. Turf becomes thin because the surface layer blocks air and water movement and creates poor footing, especially on putting greens and shaded compacted areas.

Why It Develops

Frequent irrigation, poor drainage, compacted soil, low air movement, shade, low mowing, and weak turf density keep the surface wet long enough for algae to dominate.

Reduce Disease Pressure

• Correct irrigation overlap and standing water.
• Aerify compacted soil and manage excess thatch or organic matter.
• Improve sunlight and airflow where practical.
• Restore turf density with appropriate fertility, mowing height, and traffic management.

What University Research and Extension Guidance Says

The University of Kentucky's 2024 guide reports strong research performance from several contact and combination products, including chlorothalonil- and mancozeb-containing programs, but it also warns that copper products can injure turf under some conditions. Fungicides suppress the surface growth; they do not correct the wet, compacted site that allowed it to develop.

Choosing and Using a Fungicide

Use the products below as a starting point, then match the active ingredient, FRAC group, turf species, use site, timing, rate, interval, and watering directions to the current product label. Preventive or very early applications are usually more reliable than rescue treatments after extensive injury. Rotate effective FRAC groups and combine fungicides with the cultural changes above.

Research and label note: University research may identify useful activity even when a current product label does not name this disease. That is research evidence, not a label direction. Apply a product only where the turf or application site and use pattern are permitted, and follow the complete label and applicable state requirements.

University sources: University of Kentucky: Chemical Control of Turfgrass Diseases 2024.