April showers are bringing forth rubbery yellowish-green or bluish-black blobs of the cyanobacterium, Nostoc commune (Nc). The ballooning blobs are the hydrated form of this ancient organism. Most of the time, it looks like a black, crusty substance devoid of life.
Nc commonly gets blamed for dastardly deeds far beyond its capabilities such as killing lawns. This cyanobacterium does not kill turfgrass or anything else in Ohio landscapes. Most often poor drainage weakens the turfgrass and Nc takes advantage of the free available moisture to fill in the open space.
One thing Nc can be guilty of is creating a slip-and-slide risk in nursery and greenhouse walkways. The openings to sunlight coupled with dependable irrigation create perfect conditions for a mucilaginous mass as slippery as ice.
Interestingly, cyanobacteria aren’t like most bacteria. The Integrated Taxonomic Information System (ITIS) lists 25 phyla in the kingdom Bacteria. Only 6 phyla include photosynthetic members. Five of these are anoxygenic meaning they can’t oxidize water to release oxygen. Only 1 phylum, cyanobacteria, is able to oxidize water to release oxygen.
Don’t Call it “Blue-Green Algae”
Cyanobacteria have long been mislabeled as "blue-green algae” because they produce their own food through photosynthesis and release oxygen, like algae and other plants. They also have slightly bluish-green photosynthetic pigments in their cytoplasm. However, calling a cyanobacterium an alga because they both use photosynthesis is like calling a sparrow a Boeing 747 because they both fly.
Cyanobacteria lack membrane-bound nuclei; a condition that makes them a Prokaryote. Algae and you and me are Eukaryotes. We have nuclei that are wrapped in a membrane.
Cyanobacteria have a number of other interesting tricks up their prokaryotic sleeves. They are single-celled organisms that can exist in multicellular states with chains of cells stuck together within a sheath to form a filament. This allows the cells to communicate and share nutrients over a large area which is how many Nostoc species form large mats.
Cyanobacteria have specialized cells called heterocysts that can grab nitrogen out of the atmosphere in a process called "nitrogen fixation" to convert the nitrogen into molecular forms that make the element available for the bacteria as well as plants.
For this reason, some cyanobacteria may be found growing on the surfaces of plants, including certain algae, which once added to the confusion with learning the true identity of these unusual bacteria. Some, such as Nc, also have specialized pigments in their cells that absorb UV light to protect against UV radiation. This allows this bacterium to survive intense solar radiation.
In fact, Nostoc spp. has a worldwide distribution and may be found thriving under some of the most extreme environmental conditions. Some biologists consider them to be a type of "extremophile" which is important to remember when you're trying to eliminate them!
An ID Challenge
Nc and others in this genus of unusual organisms are often misidentified because of their changing appearance. During periods of wet weather, like now, Nc may look like an agglomeration of rubbery material "bubbling up" from the soil. Colors range from yellowish-green to bluish-green as Nc hydrates and the cells become active.
The otherworldly appearance of hydrated Nc is responsible for several common names. It was once believed the alien-looking masses originated from the dust of shooting stars (a.k.a. meteors) which accounts for the common names of star-jelly, star-shot, and star-slime. Other common names such as "witch's-butter" are self-explanatory.
During periods of dry weather, the odd-looking masses collapse and turn black. In fact, dehydrated Nc is the form of this cyanobacterium that is most commonly encountered in landscapes, nurseries, and even drainage ditches.
Drying occurs quickly; however, this causes no harm to the cyanobacteria. It's a survival strategy supported by a range of polymers that keep the overall structure intact.
The bottom line is that Nc and other mat-forming members of this genus are not toxic; they cause no harm to plants or animals including harm to the health of concerned Ohio landowners. However, the mucoid-hydrated mates can become slippery when wet, so tread carefully.
Almost as Old as Dirt
There are a number of evolutionary connections between cyanobacteria and the rise of plants. Biologists generally agree that chloroplasts in plants have their ancestral origins with cyanobacteria through an evolutionary process called "symbiogenesis." Without cyanobacteria, higher plants as we know them would not exist. In fact, neither would we.
Earth has been around for about 4.43 billion years. Some believe our planet has been around slightly longer, but what are a few million years among friends? There was no oxygen in Earth's early atmosphere for the first couple of billion years; it was "anaerobic."
That didn't mean life didn't exist, but the life forms that evolved lived without oxygen. Some of those anaerobic microbes still exist, but not where they're exposed to the oxidizing effects of oxygen.
The geologic record shows that something remarkable started happening around 2.45 billion years ago. It’s called the Great Oxidation Event (GOE) and although it happened in a series of stages that “only” took around 400 million years, the ultimate outcome was the Earth’s atmosphere changed from anaerobic to aerobic.
The GOE is marked by bands of rust (iron oxide) in rocks. The rust was deposited as “free” iron (Fe) met newly liberated oxygen (O). Of course, the marriage was on the rocks from the beginning, literally.
Cyanobacteria, with their capability of pumping out oxygen, arrived on the scene somewhere around 2.45 billion years ago, perhaps a bit earlier. Although there remains some debate as to whether or not these photosynthetic bacteria were entirely responsible for the GOE, it's still generally accepted that these remarkable bacterial oxygen pumps played a significant role in pushing atmospheric oxygen toward the current 21% that we enjoy today. So, you should thank cyanobacteria with your next breath.
Managing an Ancient
Nc is a remarkable organism that causes no harm and has even been investigated for use in land reclamation sites. However, it and other cyanobacteria in this genus can grow in large mats that present a slippery safety concern in nurseries and greenhouse walkways. Blackened, dehydrated colonies can create an unsightly mess on the bottoms of plant containers. The same is true with colonies growing in gravel driveways.
Still, it's impossible to entirely eliminate an organism that has survived several mass-murder events from rampaging volcanoes releasing torrents of lava (flood basalts) to a dinosaur-killing meteor strike. However, here are some points to consider when developing management strategies for this most ancient of ancient organisms.
Water: Nc is a terrestrial organism that can survive long periods looking like blackened, dried-out mucus. However, it must have periodical infusions of water to thrive. So, moisture management through improved drainage is essential. This includes addressing both shallow as well as deep drainage issues.
For example, dried Nc mats can clog the drainage holes in weed control fabrics. Using a coarse-bristled push broom to remove dried Nostoc can open the drainage holes. Of course, nothing will be gained if the underlying soil does not drain rapidly.
Fertilizer: Although Nc can generate its own food and grab nitrogen from the atmosphere, it must acquire other nutrients from its environment. In fact, phosphorous is considered the most limiting nutrient in Nostoc development. This has also been observed with the aquatic cyanobacteria that periodically foul lake waters, but don’t call the problem "algal blooms!" So, limiting phosphorous runoff can also reduce the development of terrestrial Nostoc mats.
Chemicals: Algaecides such as sodium carbonate peroxyhydrate and copper sulfate products provide limited to no control of Nc; it's not an alga. Herbicides such as glyphosate (e.g., Roundup) not only provide no control (it's not a plant), but the release of phosphorus from dead plants can actually support Nc growth.
Herbicidal soap products based on ammoniated soap of fatty acids or potassium salts of fatty acids provide limited efficacy. However, trials conducted by Oregon State University (the Other OSU!) showed that the most effective herbicidal product is Scythe (pelargonic acid). Not only did Scythe kill Nc but it also prevented regrowth for several weeks and this product is labeled for treatment of algae, moss, or liverworts in container nurseries. Of course, hydrated Nc must be targeted, dried mats are not susceptible. Also, this contact herbicide can damage or kill preferred plants so avoid direct contact as well as drift.