Witch's jelly Nostoc spp.

Algae are primitive, root-less plant-like organisms that we generally associate with the green scum which forms in ponds. Nostoc spp. are not plants but bacteria, specifically photosynthetic cyanobacteria. They form dark green gelatinous masses on persistently moist surfaces such as nursery ground cloth, black plastic, or gravel pads. When wet, these mats of tissues are slippery, creating safety hazards. Without water, plants dry quickly to a flaky brown mass that is easily scraped off, but will return rapidly when irrigation is resumed. Algae can be reduced by improving drainage and irrigating earlier in the day to allow surfaces to dry during the day. No chemical treatments are specifically labeled for these plants.