Yellow Spot

During summer stress periods “Yellow Spots” may appear primarily on creeping bentgrass greens, tees, and fairways. As the name implies these spots may be the size of a tennis ball to slightly larger and may be numerous. The cause of these spots has not been conclusively determined but two different views on the cause have emerged. Some consider the problem to be caused by Curvularia, while others suggest cyanobacteria (blue-green algae).

The current evidence points to two species (Phormidium, Oscillatoria) of cyanobacteria to be the cause of the problem. Dr. Peter Dernoeden at the University of Maryland (U.S.A.) in a presentation provided strong circumstantial evidence that the cause is algae. He based this on the spread of filamentous algae up on the leaf blade that occurred during the night. Adding to the circumstantial evidence he found in his fungicide studies that the “yellow spots” were prevalent in all of his treatments except the chlorothalonil and mancozeb plots. Both these fungicides, especially chlorothalonil, are active on algae. A subsequent paper supported Dr. Dernoeden’s observations (1).

If you should notice yellow spots on your bentgrass turf, check closely if you can see any algae present. If treatment is warranted use an algae controlling product.

Photographs: The two photographs show the symptoms of “Yellow Spot” caused by blue-green algae (cyanobacteria)


1. Tredway, L.P., L.J. Stowell, and W.D. Gelernter. 2006. Yellow spot and the potential role of cyanobacteria as turfgrass pathogens. Golf Course Management.


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