Cyanobacteria / "Blue-green Algae"

Hosts, Symptoms & Signs

• black layer on thatch or thinned grass
• problem in areas that are heavily shaded, have poor drainage and high levels of phosphorus
• in large numbers, they move up on grass blades or cover the ground
• release of toxins causes grass to turn yellow and sometimes die

Disease Cycle

• blue-green algae are not algae, but are classified as cyanobacteria
• cyanobacteria can survive in habitats from aquatic to desert environments, including irrigated turfgrass
• cyanobacteria is most frequently found in wet, compacted, poorly drained, thin turf areas in shade, but may be found under drier conditions
• conditions that encourage cyanobacteria growth in turfgrass include warm temperatures, light that reaches the soil, excess moisture, soil layering, excess nitrogen and phosphorus

IPM Recommendations

• Minimize shade and excessive moisture.
• Aerate compacted/layered areas.
• Increase height of cut.
• Avoid phosphorus-containing fertilizers.
• Apply a fungicide (Chlorothalonil) three times at 7 day intervals.

Note: QoI (Quinone outside inhibitor) fungicides such as Heritage and Insignia could make the problem worse.