Definition
Algal leaf spots are diseases of plant foliage caused by one or more species of the plant-parasitic algal genus, Cephaleuros.
Discussion
Cephaleuros species are the only plant-parasitic algae known to cause plant disease. All other algae found on plant leaves or stems are non-parasitic. C. virescens has a relatively wide host range, but infection is mostly dependent on frequent wetting of leaves and the presence of high humidity in the plant canopy.
Management
Algal leaf spot disease usually does not cause enough damage to plant growth or yield to warrant its management by growers. Generally it only causes cosmetic damage. Because algal leaf spot disease occurrence depends upon high humidity in the plant canopy and long-duration periods of leaf wetness, pruning of affected plants to allow increased air circulation and more sunlight can reduce or eliminate the symptoms.