With the recent dry weather encouraging the use, and possible overuse, of irrigation systems coupled with rainfall and humidity, I have had several pictures and questions about a jelly-like substance growing in the turf. The jelly-like “stuff” is a Nostoc algae, a genus of cyanobacterium formerly classified as blue-green algae. It has multiple common names like star jelly, witch’s butter, and others.
According to Dr. Clint Walt, UGA Extension Turfgrass Specialist, “under warm temperatures Nostoc may appear suddenly in lawns, and other turf areas, following a period of rain and can be an indication of overwatering.” In turf, it is generally on a site where the grass is growing poorly due to severe compaction, overwatering, or both.
The algae itself does not cause turf decline or death; rather much like lichens or Spanish moss on trees, Nostoc algae colonizes areas where it has favorable growing conditions. Generally, this is in an area where the grass was already thin. Poor drainage and compacted soils create a favorable environment for Nostoc. It will dry-out if the water or rainfall diminishes but it has only gone into dormancy. With enough moisture, it will come back to “life”.
In its hydrated, gelatinous, green state it can be a safety hazard. It is slippery. Be careful walking on it. On the other hand, when it dries out, the algae can become restrictive to turfgrass growth. Nostoc dries into a black crust that can prevent stolons from rooting, or “tacking”, into the soil, delaying turfgrass growth and spread.
Nostoc can be difficult to control. To discourage its growth, encourage the growth of the grass. Algae is less of an issue with an actively growing grass canopy. If you have an irrigation system, the first step is to check the system to make sure it is watering properly (i.e. not too frequently or too much). The turfgrass species we grow in Georgia perform better when grown on the slightly dry side, so scaling back the irrigation and adjusting the irrigation schedule will benefit the grass and can discourage the algae.
Another control tactic would be to improve internal soil and surface drainage. Core aeration opens the soil, allows oxygen into the root system, and reduces compaction. While allowing the soil surface to dry-out then breaking up the Nostoc “crust” by scarifying the upper ¼- to ½-inch can break the algae into pieces and encourage its spread, it also permits the turfgrass stolons to root into thin areas and outcompete the Nostoc. With proper irrigation and core aerification the grass can cover and eventually predominate the area where the Nostoc was present.
