Black mold in grass

Lawn Slime Mold: How To Prevent This Black Substance On Lawns

The vigilant gardener may wonder, “What is this dark stuff in my lawn?” It is slime mold, of which there are many varieties. The black substance on lawns is a primitive organism that is actually beneficial. It creeps along leaf blades eating dead organic matter, bacteria and even other molds.

Slime mold on grass is not damaging to the turf, but if appearance is a problem you can remove it. You might think this mold turfgrass disease should be killed to protect the health of your grass. However, treatments are not effective and this interesting organism might be better left undisturbed. This is something you decide after you learn a few facts about lawn slime mold.

Lawn Slime Mold

Although most often you will find a black substance on lawns in moist warm conditions, slime mold can come in many colors. The individual spores can be cream, pink, blue, orange or red. When the spores mass together, the

appearance is generally quite dark but it might also appear whitish.

Slime mold spores deposit on grass when wind drives them. If moisture is present, the spores bloom and reproduce, creating patches up to six inches across.

Lifecycle of Slime Mold on Grass

The mold spores may remain viable for many years until the proper conditions occur. Slime molds come and go as moisture recedes or if temperatures are too hot or cold. When the perfect amount of moisture comes around again, you will likely find lawn slime mold in the same areas.

Heavy rains will obliterate the patch but it may also spread the spores. The best conditions for slime mold on grass to form are where there is plenty of organic material or a thick thatch, moderately moist soil, cool nights and warm days (which promote the formation of dew), and temperatures between 50 and 80 degrees Fahrenheit.

Treating Slime Mold

Because it is not really a mold turfgrass disease like rust, slime mold is good for your lawn. The only drawback to the spores is the aesthetics of it on your lawn. If the sight of the colorful patches offends you, simply rake it up off the blades of grass. You can also wipe it off with a broom or just mow over the afflicted blades.

The gunk may come back if ideal conditions still exist, but it is easy to remove—although repetitious. Treating slime mold with a fungicide is not recommended and there are no available chemicals recommended for control of the spores.

It is best to be adaptable and just live with the stuff. The spores will clear up many of the bacteria, bad fungal spores and excessive organic matter on your lawn, leading to a greener, healthier turf.

Slime Mold – Lawns

Slime molds don’t cause diseases on turfgrasses but occasionally cause concern when they suddenly appear as white, gray, or purplish spore masses on the blades. They are not parasitic on grass but feed on other microorganisms, such as other fungi and bacteria in the soil and thatch.

Susceptible Grasses

· Since these fungi use the leaves and stems of grasses only for support of their reproductive spore masses they may occur on any turfgrass species.

Primary symptoms

· The most obvious symptoms are the various colored spore masses, white, gray, brown, purple, or black, that suddenly appear on the grass blades.
· The spore masses, when young are sticky to the touch, but when dry, can be easily rubbed or wiped off.


· Slime molds can thrive and reproduce any time of the year during warm wet weather.

Environmental Conditions

· Warm weather and abundant moisture favor slime mold reproduction.


· Control measures are unnecessary since these fungi don’t damage turf.
· Spore masses can be removed from turf blades by a strong stream of water, mowing, or raking.
· Frequent mowing often is the best treatment.

Slime Mold

Scientific Name: Mucilago spp.

Primary Grass Affected: All grass types

Brief Description: Light layer of blue-gray, yellow, or black dust coating the grass blades in irregular patches.

What is Slime Mold?

Slime Mold is caused by the fungus Mucilago spp., and grows best in hot, humid conditions, usually requiring temperatures or 75 degrees F or higher. Being non-parasitic, it is one of the less harmful lawn diseases and should do no long-term damage to your lawn. Though the fungal spores that give the disease color can block some light from the grass blades, it is uncommon for the grass to turn yellow beneath it.

Most forms of Slime Mold can be eradicated simply by raking the grass. If left to its own devices, Slime Mold will vanish on its own within weeks. Because there are different types of slime molds, they may infect your lawn from spring through summer, though they are more common in late summer when the weather is warmer.

Signs and Symptoms of Slime Mold

This fungal disease is bright and showy, standing out in a green lawn with its unhealthy looking colors (blue-gray, yellow, black). Contrary to its appearance, Slime Mold will do little if any long term damage. After a few weeks the color naturally recedes, leaving your lawn as it was, though some slight yellowing due to the spores blocking sunlight from the grass blades is possible.

The less common varieties of Slime Mold will not appear on your turfgrass but instead on any wood-based materials that you may have on your lawn. These Slime Molds, fairly common in and near forested areas, are transported via the wind and have an even more striking appearance, often compared to “scrambled eggs” and “dog vomit.”

How to Prevent Slime Mold

In order to prevent Slime Mold, it is a good idea to reduce humidity on your lawn in the summer as much as possible by watering early in the day before the sun can heat the moisture left on the grass blades. Core aeration can also help to reduce humidity and limit the spread of Slime Mold during the cooler months when the disease spreads. Additionally, avoid applying nitrogen to aid the growth of your lawn while Slime Mold is active. Fungicides are rarely necessary after an infection, though they could be used to prevent an infection.

Need Help with Slime Mold?

Call Green Lawn Fertilizing today at 888-581-5296 and let’s talk about how we can help you with Slime Mold and other lawn diseases.

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Nostoc: A green, jelly-like substance growing in lawns

Within the category of “what is it?” lives a strange-looking organism called Nostoc. I first saw it a few summers ago when several people brought in samples of a green, jelly-like substance growing in their lawns, and someone has brought it to my office every year since then. After a bit of digging the first time, I identified the stuff as Nostoc sp., a genus of cyanobacterium formerly classified as blue-green algae. Nostoc has many colorful names including witches’ butter, mare’s eggs and meadow ears, among others. In fact, one of the earliest names for it was star jelly, based on the belief that it was a remnant of shooting stars fallen to earth.

Following a period of rain, it may appear suddenly in lawns, pastures, paved surfaces, roofs or stones. Michigan State University Extension has even reported Nostoc a problem in commercial nursery production. It can be hazardous on paved surfaces as it is very slippery when wet. When found in lawns, it is generally on a site where the grass is growing poorly due to severe compaction, overwatering or both. It has not caused the lawn’s decline; it has simply colonized an area where it has favorable conditions to grow. Poor drainage, compacted soils and fertilizers containing phosphorus create a favorable environment for colonies of Nostoc.

Nostoc can be difficult to get rid of. From its gelatinous, green state, it dries to a black crust that comes back to life when there is sufficient rain. To discourage its growth, improve drainage and eliminate phosphorus fertilizers. Products that contain potassium salts of fatty acids may be used to kill it in lawns. Three such products are Bayer Advanced Moss and Algae Killer, Safer Brand Moss and Algae Killer, and Garden Safe Moss and Algae Killer Concentrate (there may be others). They must be used carefully according to label directions, or damage to turfgrasses may occur. Core aerating the lawn to reduce compaction may help, but tilling the soil will merely break it into more pieces and encourage its spread. For paved surfaces and small patches in lawns, shoveling it up and discarding it in a landfill may be an option.

Although we may not appreciate it growing in our lawns or on our pavement, consider that Nostoc possesses many redeeming properties. Several Nostoc species have been used as both a food and medicine for centuries, and have more recently been evaluated for their pharmaceutical properties, including antibacterial metabolites, cholesterol regulation and control of certain cancers. They also have potential for being utilized to produce biofuels. They have the ability to fix nitrogen from the air and contain pigments which allow them to use the sun’s energy for photosynthesis. The chloroplasts in plants are believed to have evolved from cyanobacteria. They contain compounds capable of absorbing ultraviolet light, which allow them to withstand extreme UV radiation. There are species adapted to water and land that are able to withstand extreme temperatures, like those present in pools of water near active volcanoes, or in the Artic. Cyanobacteria were most likely the first organisms on earth to release oxygen into the atmosphere, setting in motion the development of higher plant and animal forms.

Slime on the lawn

This year in particular, what I jokingly refer to as “the lawn” has been invaded by blobs of black jelly, about an inch or so in diameter, on the rare occasions that we have had any rain. They seem to dry up as soon as the weather does. Have you any ideas as to what they may be, and how to get rid of them, or better still, how to prevent them?

Maggie Drake – Painswick, Gloucestershire

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It is not uncommon for these nasty-looking jelly-like algae – and also related dog-lichen, liverworts and mosses – to appear on lawns during summer damp spells, and when they do they always look alarming.

The causes of such proliferations are more or less the same: poor drainage, compaction and a large element of shade/drip cast by tree or shrub canopies, coupled with low soil fertility, all of it causing the turf to grow poorly.

There are no chemicals available to gardeners specifically to control this nasty (technically a cyanobacteria called Nostoc), although moss killers may help.

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You could help the situation for next year by improving the drainage of the soil by aerating, then apply a layer of sandy top dressing in the autumn or spring as well as appropriate lawn fertilisers (high nitrogen in spring, high phosphate in autumn).

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Credit: Getty Images Credit: Alamy

Mystery of seasonal moisture: blobs of goo also known as ‘star jelly’

Blobs of strange, sometimes repellent, substances, appearing suddenly on the ground, have puzzled people for much of history. Queries to “Eye on Nature” often offer three separate examples.

In times past, popular explanations looked to the sky for the origin of translucent goo, deposited on grass or branches of trees, and thus became “star jelly”, perhaps brought down in meteor showers.

Research at Britain’s Natural History Museum traced samples to the unfertilised spawn of female frogs, coughed up from the gullets of predatory herons.

Scattered masses can look like scrambled egg

Seasonal moisture counts more in other, more regular, mysteries. Slime mould is a strange, cellular organism that is neither fungus nor animal but shares ancestry with both. Scattered masses can look like scrambled egg or dog vomit and can actually creep about, if very slowly, in search of bacterial food.

Another rain-loving organism, appearing suddenly on gravel paths, is like glossy and slippery seaweed when swollen with water, and dog-shit when flaccid and dry. In neither form have “Eye on Nature” readers found it welcome underfoot, especially in well-manicured gardens.

This one is nostoc – in science, Nostoc commune. Long intrigued by its odd name, I set out through Google’s spider-web of knowledge and ended up at an ecological story as broad as the planet itself.


As one of the algae, the first stop for nostoc was at the online encyclopedia created and curated by Prof Michael Guiry of NUI Galway. He shows examples of “witch’s butter” (also a folk-name) from paths in the university grounds. Another that he photographed, used for my drawing, was glistening this autumn at the base of a city wall.

A common surface for nostoc is limestone gravel, used throughout Ireland on paths, drives and flat roofs and especially inviting to nostoc in the ever more showery, poorly-drained west.

Dr Guiry found nostoc – in the wild, as it were – on sand dunes on Clare Island, where calcium is offered, instead, in the powdered shells of marine molluscs. And nodules of a similar nostoc species litter limestone hollows of the Burren.

Dr Guiry accords nostoc the same stellar folklore as the regurgitated frogspawn. This is echoed by an American scientist, Malcolm Potts, who has explored the original naming of nostoc (in International Journal of Systematic Bacteriology, April 1997).

Star-snot is also among folk names for the errant frogspawn jelly

It was coined, he suggests, by the 15th century German scientist, philosopher, folklorist and alchemist remembered respectfully as Paracelsus. Familiar with “the gelatinous colonies of the ubiquitous terrestrial cyanobacterium Nostoc commune”, Potts proposes, Paracelsus played on fables of “excrement blown from the nostrils of some rheumatick planet”.

In “nostoch” – first with an “h” – aracelsus melded German and Old English words for the nose. Potts points to the alga’s distinctive, earthy smell and the flow of its prodigious swelling in the rain. (“Star-snot” is also among folk names for the errant frogspawn jelly.)


The dramatic inflation of nostoc adds to its fascination as an organism of dormant perhaps even “ancient” cells, tolerating long periods of desiccation before revival by rain and spreading when broken into fragments. More research led by Malcolm Potts found that drying out for up to 60 years can leave its cells undamaged and ready to swell again, which may explain some of its appearances “from nowhere”.

Nostoc has no need to be “for” anything of human benefit: its value is to many natural ecosystems

As a cyanobacterium, or blue-green alga, nostoc belongs to the vastly varied global tribe of microbes which, more than two billion years ago, began producing oxygen through photosynthesis, thus creating the atmosphere that lets us breathe.

But nostoc has no need to be “for” anything of human benefit: its value is to many natural ecosystems. Deserts of the southwest US, for example, Nostoc commune is part of surface crusts that, as a sink for CO2 and fixer of atmospheric nitrogen, help the stability and fertility of the soil and the growth of its lichens and mosses.

Complaints about Nostoc commune (even some by lawn-proud gardeners in New Zealand) fit oddly with reports of its use as food and the possible risks in eating a lot of it. Dr Potts takes the story back some 1,600 years to China, when the alga “was used as a staple food by Hung Ge, a renowned alchemist and hermit”.

A different, filamentous, species of nostoc is also used today in making China’s bird’s nest soup. But concern about current consumption of Nostoc commune in the highlands of Peru and in city folk markets and restaurants came in 2008 in the Journal of Ethnopharmacology.

The alga, reputedly highly nourishing in the rainy season, was found to produce a neurotoxic amino acid suspected of links to Alzheimer’s or Parkinson’s diseases. But this research sampled it in “globular colonies” called llullucha, whereas the swollen mats in Ireland offer only ear-shaped bubbles. Even so it’s best, perhaps, to leave them on the gravel.

Slime Molds on Turfgrass

Slime molds may be found on all cultivated and weedy grasses. They are most prevalent following prolonged periods of leaf wetness and may be observed from late spring to late fall. Although not directly damaged by slime molds, the aesthetic quality of a turfgrass stand may be affected by their presence. Plant vigor may be slightly reduced in severely colonized turf due to excessive growth of the fungus on leaves causing a shading of the leaf surface and leading to a reduction in photosynthesis. Slime molds may reoccur in the same location each year.

Causal Organism

Slime molds are “primitive” fungi that use the living turfgrass plant strictly for structural support. They are saprophytes, or organisms that obtain their nutrients solely from dead or decaying organic matter in soil or thatch. Most fungi causing slime mold on turfgrass belong to either the genera Mucilaga or Physarum. Slime molds are most prevalent following prolonged periods of leaf wetness, which favor the growth and development of the fungus. Areas with poor drainage and heavy thatch also may enhance the likelihood of their development.

Slime mold on leaf blade. Slime mold on turf.


There are various species of slime molds, each resulting in a discolored, irregular patch ranging from several inches to several feet in diameter. Discoloration is due to extensive sporulation by the fungus. In general, small capsule-like spore masses, each about the size of a pinhead, grow perpendicular to the surface of the leaves. These fruiting bodies are typically grayish-white to blue-gray or ash colored and contain purple spores. Some slime molds appear as thin, white, yellow, or gray layers of slimy pastelike material that covers the leaf blades. These masses later dry to form bluish-gray, black, or white powdery growths on the leaves. At this stage, the grass has the appearance of having been dusted with soot. In the case of heavy spore production, some yellowing or chlorosis of the leaves may be observed due to shading of the turf causing reduced photosynthesis.


The recommendation for areas experiencing light to moderate slime mold infestations is to simply let nature take its course. Heavy infestations can be removed via mechanical means such as mowing, raking, or using a forceful spray from a garden hose. Washing the leaves with a stream of water should be attempted only after the onset of dry weather to avoid further development or spread of the fungus. Chemical management is not typically recommended.

Black Mold on Bermuda Grass

hose on lawn image by Coralie Palmeri from

Black mold (Physarum sp. and Fuligo sp), commonly called slime mold, produces a grayish-black covering over the grass blades of Bermuda grass and other warm-season turfgrass varieties. The fungus causes no lasting damage to the grass but it does render it unsightly. The fungus grows prolifically in the southern United States, where it prefers warm, humid conditions.


Large circular or irregular circles of black or grayish-black mold appears on the surface of the Bermuda grass. The slimy mold appears like dark oil on the grass until it produces fruiting bodies that create a crusty residue on the grass blades. The fruiting bodies contain thousands of black spores that are released into the air so the mold can reproduce. In an extreme infestation, the slimy, black mold may cover the entire surface of the Bermuda grass.

Long-Term Effects

Despite the unsightly appearance of the slimy black mold on the surface of the grass, it does little damage to the grass itself. The mold usually lasts a few weeks. After the release of its reproductive spores, the mold begins to die away. The grass is left virtually untouched after the mold disappears, according to Alabama A&M and Auburn universities.


The mold often appears in the same spots on the Bermuda grass every few years. The mold will make its first appearance during the spring or summer when conditions are humid. After several days of heavy cloud cover, the homeowner will often notice the black slime. The mold will occur predominately on the Bermuda grass blades, but the homeowner may also notice the mold covering bark chips, mulch, leaves or twigs.


Lightly raking the area when the black mold first appears will often eliminate or help reduce the appearance of the mold dramatically as it grows. Mowing will also remove the fungus but it often returns within a day or two. Simple washing with a heavy stream of water on the surface of the grass will often wash the mold away successfully. Washing the area with a solution of 1 tbsp. dish soap to a gallon of water will kill the mold, according to Mississippi State University.

Warning and Solutions

Avoid using fungicides on Bermuda grass afflicted with black slime mold. It has no effect on the mold. Keeping the grass healthy will often prevent the growth of black slime mold on the grass. Yearly thatch removal also appears to help. Areas of the lawn that drain poorly often suffer from black mold. Consider building up the area to facilitate better drainage and then replant with Bermuda grass.

Picture this: As you work through your lawn, you notice a little patch of grayish growth. When you inspect it closely, you notice it resembles ash that has been sprinkled on the grass blades. When you touch it, a small cloud of dust rises off the blades.

You immediately go to your phone and call your lawn service or local nursery because you are concerned that this problem will spread. On your way to the phone, you notice something weird on the mulch that is spread across your landscape beds.

You may ask yourself the following questions:

What does Slime Mold look like?

You stop for a closer look and are appalled at what you see. It looks as if someone got physically sick and vomited in your flowerbed. You think, “How disgusting” — Yes it is! But, is there anything to be worried about — No there is not! Both of these “conditions” are caused by primitive fungi known as Slime Molds.

What Is Slime Mold?

Slime Molds are saprophytes, or organisms that obtain their food from dead or decaying organic matter. They will creep along the soil surface in search of food by pulling themselves along with finger-like projections. During periods of warm, rainy weather, Slime Molds will creep up on grass plants, on the lower branches of ornamental plants, or across landscape beds covered with mulch when they are ready to reproduce.

From these locations, they will release millions of tiny spores. Spores are like tiny seeds that will help ensure many more generations of Slime Molds. The only purpose for creeping up on the plants or mulch is to give the spores the best advantage for distribution over a large area.

Will Slime Mold Hurt My Lawn?

Since Slime Molds are not lawn disease that damage plants, but are actually beneficial to the ecosystem of your landscape, control is not necessary. If you find the dried patches in the lawn, help Mother Nature by sweeping the spores into the wind. The slimy patches in the mulch will dry and can be raked under. They may be unsightly, but should not cause any concern in terms of your yard care. They are just part of the wonderful world of nature.

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FAQ – Sometimes I get mold on top of my mulch. What is it, and is it harmful?

During periods of heavy rain or excessive watering a yellow mass can form on organic mater and plants. It is called Fuligo septica; or commonly know as Slime Mold or Dog Vomit.

While the appearance of this mold may raise a high level of concern the first thing you should know is it is not toxic and will not harm your lawn, garden or plants.

It feeds on moist organic mater and forms a yellow patch which will turn a greyish-ivory color.

The best way to get rid of Slime Mold

  • Expose it to light, sunshine and dry weather whenever possible for a natural way to get rid of it.
  • Dig out the slim mold. This is the cheapest way to get rid of it. However, it is possible for it to come back. Just remember not to over water this area.

How not to get rid of Slime Mold

  • Do not spray water on it to dissipate to remove it. This chain reaction started because there was too much moisture, remember.


  • Allow nature to take its course. Slime mold of this type won’t hurt your lawn or garden. Dry air and sunshine will usually do the trick
  • If you have irrigation be sure to water these areas less.

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