Symptoms

• Algae cause a green or black scum to form on bare or very thick turfgrass. It starts out slimy but eventually turns into a thin, dark-green or black crust. The crust eventually cracks. The grass may become weakened and yellowish in color and may die from the algae.
  
  

Management

• Perform a soil test to determine the correct amount of lime or fertilizer the soil needs, if you notice algae forming. Avoid using excessive amount of water and use a rake to break up the algae. The University of Missouri Extension states that improving soil drainage also helps to stop the spread of algae.
  
  

Recommendations

• Before reseeding the grass, apply 5 to 10 ounces of lime or other fertilizer for every 1,000 square feet of soil. Maintain the proper pH and nutrition levels for the soil in your area. Increase the height you mow the grass to, because it is harder for black algae to bind to taller grass, according to the Iowa State University's Horticulture & Home Pest News site.