With the recent dry weather encouraging the use, and possible overuse of irrigation systems, and then the recent tropical conditions (high rainfall and humidity), we have had several pictures and questions about a jelly-like substance growing in lawns. The jelly-like “stuff” is a Nostoc algae, a type of cyanobacterium formerly classified as blue-green algae. It has multiple common names like star jelly, witch’s butter, and others.
Under warm temperatures Nostoc algae 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 soil compaction, overwatering, or poor drainage. It does not cause turfgrass decline or death; it colonizes areas where it has favorable growing conditions and 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. However, when it dries-out it can become restrictive to turfgrass growth. Nostoc dries into a black crust that can prevent grass 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 turfgrass canopy. The first step is to check the irrigation system to make sure it is watering properly (i.e. not too frequent or too much). The turfgrass species we grow in Georgia perform better when grown slightly on the dry side, so scaling back the irrigation and adjusting the irrigation schedule will benefit the grass and can discourage the algae.
The equivalent of 1” inch of water every 7 to 10 days is all that is needed to keep lawns happy and healthy. Ideally, this amount of water should be applied in one or two applications per week and allow a few days for the soil to dry out between watering. Adjust the amount applied each week based on local rainfall amounts. If we get a half inch of rain then wait a few days and irrigate another half inch if no more rain is in the forecast. If we get an inch or more of rain, then turn your system off for a week and save money on your water bill. Watering in the early morning hours before 10:00am will allow the grass and soil surface to dry out more quickly. This will also help minimize turfgrass disease pressure and keep your grass healthy.
Improve internal soil and surface drainage if necessary. Core aeration opens the soil, allows oxygen into the root system, and reduces compaction. Aerating the soil will help dry-out and break up the Nostoc “crust” on the upper surface. Breaking the algae into pieces may encourage its spread, but 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.
This article was reprinted and adapted with permission from Dr. Clint Waltz, UGA Turfgrass Specialist.
Paul Pugliese is the Extension Coordinator and Agricultural & Natural Resources Agent for Bartow County Cooperative Extension, a partnership of The University of Georgia, The U.S. Department of Agriculture, and Bartow County. For more information and free farm, lawn, or garden publications, call (770) 387-5142 or visit our local website at ugaextension.org/bartow.