This revolting slimy algae is forming on gravel/stone surfaces ~ pathways, carparks, cobbles. We think it’s Nostoc. First (modest) appearance was in 2010; now it’s widespread, sometimes in carpets up to 1.5cm thick (and counting).. Thrives on rain, even in this cold weather. Very unsightly, dangerously slippery underfoot. Can you suggest a chemical for control / elimination? (Drainage not an option) . (These Photos is from web; not my own.
Blue-green algae need water or damp condtions to grow. They can photosynthesize and grow on damp paths and surfaces, and in mossy lawns.
The best approach is to improve drainage by ruffling up the gravel or laying fresh gravel on top.
Otherwise, use moss-control products, Jeyes Fluid and the like. The potato blight spray Dithane can be used and copper-based sprays such as Liquid Copper can be used as they contain the heavy metal copper which has a lasting effect. until it is washed out.
Do not use any copper-based spray where it might run off into drains or streams as it is toxic to fish and other water wildlife.