Written by Sarah F.
The jelly green material growing in places in your lawn appears to be several species of algae (many of which are also known as cyanobacteria). Under the microscope, numerous algal cells were observed. We have no algal specialist on staff to identify individual species. In past samples where this type of growth has been problematic, two main issues have been noted:a) moisture is often abundant. Not much you can do about rain but if irrigating make sure you aren’t overapplying and that the drainage is good. Lawn information is enclosed.b) sometimes abundant growth is associated with a nutrient source (overfertilization is one possibility but other sources of nitrogen, such as manures/septic drainfields/etc. should be examined to see if they might be playing a role in the onset of the problem.Physical removal is probably the only practical option you have in this situation. The problem may go away when conditions are less moist. Do make sure there isn’t some potential underlying nutrient source contributing to its growth. I am attaching the information on black algae from the PNW Plant Disease Management Handbook http://pnwhandbooks.
org/plantdisease/lawn-and- turf-algae that indicates certain copper fungicides and other chemistries might help suppress the growth of algaes but are not going to completely solve the issue. Follow label directions carefully if pesticides are used.