Consistent heavy rains, coupled with warm temperatures, have re-awakened a sleeping primeval organism in southwest Ohio landscapes. The ballooning yellowish-green or bluish-black blobs are the hydrated form of the ancient cyanobacterium, Nostoc commune (Nc). Most of the time, Nc exists as black, crusty matter adhering to the soil and appearing devoid of life.
Nc is a remarkable organism that has long been utilized as a food source in some parts of the world, and has been investigated for use in land reclamation sites. Unfortunately, this cyanobacterium commonly gets blamed for dastardly deeds far beyond its capabilities such as killing lawns.
In fact, Nc causes no harm to turfgrass or anything else in Ohio landscapes. Most often, poor drainage weakens the turfgrass and Nc fills in the open space by taking advantage of the free available moisture.
However, blackened, dehydrated colonies can create an unsightly mess on the bottoms of plant containers. The same is true with colonies growing in gravel driveways.
A more serious concern is the slippery nature of the hydrated mucilaginous mass that can provide less traction than ice. Nc and other cyanobacteria in this genus can grow in large mats that present a slippery safety concern in nurseries and greenhouse walkways, as well as in weakened turfgrass.
Based on a face-to-turf experience I had last year, I can say the ice comparison is no exaggeration. Indeed, I received a question about Nc today from a homeowner who had slipped on an Nc mat near their front door.
A Remarkable Ancient
Nc belongs to a group of cyanobacteria (domain Bacteria, phylum Cyanobacteria) that are capable of producing their own food and releasing oxygen through photosynthesis. Some cyanobacteria have slightly bluish-green photosynthetic pigments in their cytoplasm that are responsible for the misnomer, “blue-green algae.”
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, and neither would we.
Cyanobacteria lack membrane-bound nuclei; a condition that makes them a Prokaryote. Plants like algae and animals like 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, slippery mats.
Nc and others in this genus of unusual organisms are often misidentified because of their changing appearance. During periods of wet weather, Nc may look like an agglomeration of rubbery material "bubbling up" from the soil. Colors range from yellowish-green as it's hydrating to bluish-green once it becomes fully hydrated 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.
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.
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!
Older Than the Hills
Cyanobacteria are, in fact, older than the hills. They’ve been around since before the rise of the Himalayas (40-50 million years ago), the Rocky Mountains (50 – 80 million years ago), and even the Appalachians (1.2-500 million years ago).
Earth has been around for about 4.43 billion years. For the first couple of billion years, there was no oxygen in Earth's early atmosphere; it was anaerobic. Our deep blue oceans at that time looked nothing like today. They were tinged in red owing to an abundance of unattached iron (Fe) dissolved in the water.
The anaerobic condition of Earth’s atmosphere 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), or the Great Oxygenation Event. It happened in stages over time that lasted for around 400 million years with the outcome being the Earth’s atmosphere changed from anaerobic to aerobic.
The series of oxidation events are marked by bands of rust (iron oxide) in rocks. The rust was deposited when the “free” iron (Fe) met newly liberated oxygen (O). One could say the marriage was on the rocks from the beginning, literally, because the iron oxide precipitated out of the oceans settling to the bottom to become layers in sedimentary rock, the so-called banded iron formations.
Some of the most dramatic examples of banded iron formations are found on Michigan’s Upper Peninsula, as shown in the image below. On a side note, unlike many other geological processes that constantly churn out new rock, the banded rocks can never be formed again.
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
It's impossible to entirely eliminate an organism that has survived several mass-extinction 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 lengthy periods, looking like blackened, dried-out mucus. However, it must have periodic infusions of water to thrive. This is the "Achilles' heel" for Nc. Moisture management through improved drainage is essential part of an Nc management plan. This includes addressing both shallow as well as deep drainage issues.
For example, “dams” created by curbs allow water to pool providing perfect conditions for Nc to proliferate. The same is true for low areas where water can collect.
Fertilizer: Although Nc can generate its own food and grab nitrogen from the atmosphere, it must acquire other nutrients from its environment. In fact, phosphorus 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 phosphorus 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 not only provide no control (it's not a plant), but the release of phosphorus from dead plants can 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 the 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.