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

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

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By: Bonnie L. Grant, Certified Urban Agriculturist

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 (15 cm.) 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 (10 to 26.5 C.).

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.

This article was last updated on

Read more about General Lawn Care

Ann Joy and Brian Hudelson, UW-Madison Plant Pathology
Revised: 4/25/2004
Item number: XHT1091

What is a slime mold? Slime molds are members of a shape-shifting group of organisms called myxomycetes. These organisms are found all over the world, even in deserts, high altitudes, and on the edges of snowbanks. Although they often resemble fungi, slime molds are more closely related to amoebas and certain seaweeds.

What does a slime mold look like? A slime mold spends most of its life as a lumpy mass of protoplasm, called a plasmodium, that moves and eats like an amoeba. It may be white, yellow, orange, or red. The color of a particular species can vary slightly with temperature, pH, and the substances the plasmodium eats. One very common slime mold, Fuligo septica, looks like dog vomit or scrambled eggs, from which it derives its common names. Others resemble a network of veins or a fan. In the course of a few hours a slime mold can transform from its amoeba-like phase into its fungus-like phase, which produces spores.

Where do slime molds come from? The most common slime molds in Wisconsin love moist, shady places like crevices in rotting logs, leaf letter, and bark mulch. Spores of slime molds are resistant to adverse conditions and will germinate after a heavy rain. The plasmodium forms from many individual swimming cells called swarm cells. The plasmodium can move at a very slow rate, feeding on bacteria, other microorganisms, and organic matter. Changes in moisture or temperature, or exhaustion of its food supply can cause the slime mold to move to a drier, more exposed location to produce spores.

What do I do with a slime mold in my garden or lawn? Slime molds do not cause diseases of plants or turf. They do use leaves and stems as surfaces on which to grow and can block out sunlight leading to leaf-yellowing. The best way to get rid of a slime mold is to break it up and dry it out. Rake up and dispose of slime molds on bark mulch. For slime molds on turf, mow the lawn, and rake up the thatch. Alternatively, you may want to enjoy a slime mold if you find one in your yard. These complex organisms are fascinating to observe and can be “captured” and grown indoors as a science project.

For more information on slime molds: Visit Tom Volk’s website at, or contact your county Extension agent.

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Growth of Dog Vomit Slime Mold

Slime molds like dog vomit produce spores that are wind-borne. They are highly resilient and can survive even during hot, dry weather. The spores can remain viable for several years, waiting for conditions to be favorable for growth. When warm, moist conditions are present, the dormant spores absorb moisture and crack open to release a swarm sphere. Shortly after, the telltale, disgusting-looking slime mold appears.

Fulgio septica often grows in wood mulches, along the sides of untreated wood, on compost, and sometimes in lawn grass, particularly if there's quite a bit of thatch in the lawn. Occasionally, it grows on plants that are growing in mulch, and if a large enough colony forms, it may smother the plant. This is uncommon, however, and you'll usually just find the mold in the mulch itself.

Prevention and cure of slime mould on lawns

The areas affected, should be aerated by spiking and also top-dressed in the autumn. Use a sandy mixture after spiking in order to improve drainage and ease compaction which is another cause of lawn slime.

Other than that, there is rarely any need for concerted action, and certainly no need to treat it with any chemical spray. Basically, it need the grass blades as a home to do its reproduction - without any parasitic action that affects the grass. As soon as it has done its business, it will disappear - normally after a couple of weeks..

Slime moulds are generally made up from a collection of single cell beings - half plant/half fungi! Singularly, the individual spores are invisible the the human eye, but tend to congregate in masses giving them the well deserved name of slime. The slime can either stay put for a few days, or can gradually spread across lawns - feeding on dead organic matter as it goes.

It can either be small patches, or larger patches that are sometimes mistakenly identified as something the cat or dog threw up!

The image shows a typical slime mould outburst .

They can sometimes be orange, yellow or brown in colour.. It can be found on any of the grasses or mixtures used in most lawns, and is not always seen a a gelatinous mass, but rather as thin strands - normally grey in colour.

As with so many other lawn problems, slime mould is happier in a slightly neglected lawn, and is not generally to be seen on a well cared for and nourished lawn. As stated above, it does not feed on grass, but relies an a supply of dead organic matter to feed. A well kept lawn will not have such matter in abundance!

Slime molds are primitive organism that exhibit characteristics of both plants and animals, although they are considered fungi. Numerous species of slime mold occur on turf the most common is Physarum cinereum. Slime molds are not pathogens and cause little more than some yellowing.

Slime molds grow on the surface of leaves and stems feeding on decaying organic litter and on other fungi and bacteria in the thatch layer in the soil. They often appear on well-maintained turf after a warm summer rain and usually reappear in the same area year after year and last one to two weeks. Slime mold spores are spread by wind, water, mowing, and other activities on the turf.

A slime mold is composed of thousands of tiny, usually purple, gray, white, or cream, sack-like spore enclosures called fruiting bodies. These form in 4- to 6-inch patches in the turf and may be widely spread or clustered into groups. The slimy growth is called a plasmodium. This dries into a powdery mass of spore-bearing bodies that coat the grass blades.

Slime molds are more of a curiosity or nuisances than a threat to the turf. Control measures are usually not necessary but if desired, slime mold can be removed by vigorous raking, mowing, or hosing down with a fast stream of water.

Fading Out

Causal agent

Susceptible turfgrasses

Perennial ryegrass, tall fescue and all varieties of bentgrass, bermudagrass, zoysiagrass and centipede

Conditions promoting disease

Similar to Helminthosporium leaf spot. Usually weakly pathogenic unless turfgrass is predisposed to high temperatures stress.


Vary with type of grass. Fescue- indefinite yellow/green dappled pattern extending down from leaf tip. Affected area turns brown, then gray, then dies. Reddish brown margin may or may not be present. In Bentgrass, affected parts of blades are tan instead of brown or gray.


Have soil test done mow during dormancy and remove clippings. Recommended fungicides can help prevent further infection while corrective cultural measures are taken.

Yellow Mold Facts and Tips to Remove It

There are various types of mold that can grow on various surfaces, and one of them is yellow mold. This kind of mold grows on a lot of things, from a wooden surface to bathroom and even grass clippings.

The yellow mold may not be as common as other types of mold that grow in a building, although this type often grows outside, including in the garden.

Since many people are not familiar with yellow mold, there are various misconceptions about the characteristics and even danger of this mold. Make sure you understand about yellow mold facts, including the right way to remove it.

What is Yellow Mold?

Yellow mold is often referred as “slime mold”, because the colony looks like bright slime when seen at a glance. A large colony of mold often shows actual fungi head growths, which look like tiny mushrooms.

There are several types of mold that can produce a yellow hue, such as Aspergillus, Meruliporia incrassata, and Serpula lacrymans.

Aspergillus is the most common genus of mold that may produce yellow hue. It can grow anywhere, from wooden surfaces, to tiles, and even foods.

Serpula lacrymans is a type of mold that often grows on wood, whether inside a building or on trees. Meanwhile, Meruliporia incrassate is a type of yellow mold that is often quite toxic.

Is Yellow Mold Toxic?

While it looks striking thanks to its bright color, there are still some misconceptions about yellow mold, especially among home owners. Yellow mold is not a super dangerous organism that will poison the inhabitants.

Healthy people with a good immune system may be able to live in a house with yellow mold, but the danger is present for vulnerable groups, such as babies and people with respiratory problems or compromised immune system.

Garden owners often do not know what to do when finding yellow mold on their mulch, lawn, or grass clipping. The truth is: this slime mold is a common organism that lives on plants or organic materials, but do not act as a parasite.

Yellow Mold on Bread

Bread is a type of food that is loved by fungi, especially since it contains a lot of nutrition. Fermented bread types are especially fertile for fungi, making it easy to get moldy.

Aspergillum is one type of mold that often grows on and inside bread. The mold looks like fuzzy layer on top and inside the bread, often with various colors instead of just one.

A really moldy bread usually also releases distinguished musty smell, common among a big colony of mold. Bread is often stored in the dark, warm place, making it more ideal for mold and fungi.

Yellow Mold on Mulch

Mulch, grass clipping, and compost heaps are among the most common locations for yellow mold to grow. Outside, a yellow mold is that slimy substance that you may confuse with animal feces or vomit.

The strange look often makes people worry about what will happen to their plants or gardens.

Yellow mold that you find on mulch, compost heap, or grass is generally harmless. While it looks bad, you can simply rake or scrape it.

The only danger is that if the yellow mold grows uncontrollably, especially in the garden, it can actually smother the plants and reduce nutrition intake they can take.

Yellow Slime Mold in Bathroom

Bathroom, shower, and a wet area in the kitchen are ideal spots for mold to grow, including yellow mold. These rooms are often damp and full of the residue of shampoo, soap, and dirt, which are foods for a lot of bacteria and single-cell organisms that form yellow mold.

Yellow mold often grows on spots such as shower walls or curtain, vent, near the faucets or shower head, under the sink, near the sinkhole, and in the corner of walls or floor.

If you seldom clean your bathroom thoroughly, or does not use cleaning agent with anti mold formula, it will be easy for yellow mold to grow.

Yellow Mold on Walls

Walls often become places for mold to grow, especially in the middle of the ideal situation. High humidity, moisture problem, and lack of fresh air or sunlight are factors that cause yellow mold to grow on walls.

Yellow mold on walls may grow into larger fungi colony, so you need to remove it when the problem is still small. Otherwise, you may need to replace the walls and wallpaper, or even remodel parts of your house to prevent new growth.

Yellow Mold on Wood

Slime yellow mold loves growing on an organic surface, especially wood. If your house structure has woods in hidden places, such as in the basement, ceiling, or foundation, you can experience mold problem after a while.

The yellow mold may start as little specks, but they can grow into a slimy layer that looks disgusting. If you let it grow, the mold will release musty smell and damage the structure.

How to Get Rid of Yellow Slime Mold

Removing yellow mold from any outdoor surfaces, such as grass, mulch, or compost heap is quite easy. You can just take the mold and remove it as far as possible from the vicinity of your garden.

However, if the problem persists, you may want to replace the soil and remove the moldy plants or mulch.

If the mold problem happens inside the house, you can spray the moldy surface with a mix between 1 part of white vinegar and 3 parts of water (you can replace vinegar with hydrogen peroxide or baking soda).

Let it soaks for 10 minutes before scrubbing the surface. However, if the problem happens on more than 10 meters of square area, call professional for better cleaning result.

If the yellow mold grows on bread or other foods, remove those items as soon as possible. Clean the storage or space where the moldy foods are previously stored, so there is no mold growing again.

Do not forget to always pay attention to your food’s expiry date or shelf life.

Yellow slime mold is not a pleasant sight at home. Make sure to deal with the early stage of mold problem as soon as possible, and prevent future yellow mold infestation problem inside or outside your house.

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