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Slime Mold on Grass: Causes, Prevention, and Treatment

Posted on June 16, 2023 by Lawn Doctor

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Slime mold on grass is a common problem that many homeowners face. Slime molds are primitive fungi that use living turfgrass plants for structural support. They appear as a slimy, creamy-white or black substance on lawns in moist and warm conditions.

Although they are not harmful to the grass, they can be unsightly and unnerving. Slime molds use the grass leaves as scaffolding to support themselves when grouping together, which the cells do when looking for food. They eat dead and decaying matter, so they can actually be beneficial for your lawn by breaking down dead material before moving on. However, they can leave spores behind, which will generate future slime mold, making it difficult to eradicate them completely. This article will provide tips for preventing and treating slime mold on grass.

What is Slime Mold on Grass?


Slime mold is a primitive organism that shares similarities with both fungi and single-celled animals. It is not a true fungus, but it can appear on numerous objects in the landscape, including grass. Slime mold on grass is a type of turfgrass disease that does not directly infect the plant. The spore-producing structures of slime molds can appear on lawns quite suddenly, sometimes overnight.


Slime mold on grass can appear as thin, white, yellow, or gray layers of slimy paste-like substance covering leaf blades. It can also appear as a blue or orange crust-like substance. A thick layer of slime mold may affect the rate of photosynthesis, and you may notice the yellowing of the plant leaves. 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 F. (10-27 C.).

Slime mold on grass is not harmful to humans or pets, but it can be unsightly. It is important to note that slime mold on grass is not a sign of poor lawn care or improper fertilization. It is simply a natural occurrence that can happen in any type of lawn.

If you notice slime mold on your lawn, the best course of action is to simply wait it out. The structures will soon disintegrate to release a mass of spores. However, if the appearance of slime mold on grass is particularly bothersome, you can remove it by gently raking the affected area. Avoid using fungicides or other chemicals, as they are not effective against slime molds and can harm beneficial organisms in the soil.

Causes of Slime Mold on Grass

Environmental Factors

Slime mold on grass is caused by a combination of environmental factors. Warm, wet weather is the most common cause of slime mold growth on grass. Slime mold spores deposit on grass when wind drives them. If moisture is present, the spores bloom and reproduce, creating patches up to 6 inches (15 cm.) across. The mold spores may remain viable for many years until the proper conditions occur.

Organic Matter

Organic matter buildup in the lawn can also lead to slime mold growth. Areas with poor drainage and heavy thatch buildup may enhance their development. Slime mold can appear on turf suddenly or overnight following prolonged grass wetness. It is usually prevalent during warm, wet weather and eventually disintegrates and disappears on its own when the moisture recedes.

To prevent organic matter buildup, homeowners should consider raking up grass clippings and other debris that accumulates on the lawn. Mowing the grass regularly can also help prevent the buildup of organic matter.

Other Factors

Other factors that can contribute to slime mold growth on grass include overwatering, poor drainage, and lack of sunlight. Slime mold is less likely to do long-term damage to your lawn than other lawn diseases like rust, but it can cause yellowing of grass blades and unsightly masses on the lawn.

Fungicides are not effective in preventing slime mold growth on grass. To physically remove slime mold from your grass, just scoop it off with a shovel and dispose of it in the trash. But eradicating slime mold is another matter altogether. That’s because the fruiting bodies leave spores behind, which will generate future slime mold.

Prevention and Treatment of Slime Mold on Grass

Slime mold on grass can be unsightly and alarming to homeowners, but it typically does not cause harm to the grass. Prevention and treatment of slime mold on grass can be achieved through both chemical and mechanical means.

Chemical Treatments

Chemical control measures are not typically necessary for slime mold on grass. However, in cases of severe or recurring slime mold, fungicides may be used. Fungicides should be used sparingly and only as a last resort, as they can be toxic to beneficial organisms and may harm the environment.

Mechanical Means

Mechanical means of removing slime mold on grass include dethatching, mowing, raking, and brushing. Removing the dry spore masses by mowing, raking, or brushing will help to return the grass to its normal appearance. Heavy infestations can be removed via mechanical means such as using a forceful spray from a garden hose.

To prevent slime mold on grass, homeowners should ensure proper lawn care practices, such as regular mowing and removing grass clippings. Slime mold thrives in humid conditions, so ensuring proper drainage and reducing thatch buildup can also help prevent its growth.

Homeowners should also avoid over-fertilizing with nitrogen, as excess nitrogen can promote the growth of slime mold. In addition, pruning leaves and branches in affected areas can allow for more sunlight and air circulation, which can help prevent the growth of slime mold.

In conclusion, slime mold on grass can be prevented and treated through proper lawn care practices and mechanical means. Chemical treatments should only be used as a last resort and with caution. By following these tips, homeowners can maintain a healthy and attractive lawn free from the unsightly growth of slime mold.

Why You Should Hire a Professional to Remove & Prevent

When it comes to dealing with slime mold on grass, hiring a professional can be a wise decision. Here are some reasons why:

Expertise and Experience

Professional lawn care companies have the knowledge and experience to properly identify and remove slime mold from your grass. They can also take steps to prevent it from returning in the future. Attempting to remove the mold on your own can be risky, as it is easy to mistake it for other types of lawn diseases or pests.

Proper Equipment and Products

Professional lawn care companies have access to specialized equipment and products that are designed to effectively remove slime mold. They also have the training to use these tools safely and effectively. Attempting to remove the mold on your own can be dangerous, as some products can be harmful to both humans and pets.

Time and Convenience

Removing slime mold from your lawn can be a time-consuming and labor-intensive task. Hiring a professional lawn care company can save you time and hassle, allowing you to focus on other important tasks. Plus, many companies offer flexible scheduling options to accommodate your busy schedule.

Long-Term Cost Savings

While hiring a professional may seem like an added expense, it can actually save you money in the long run. Professional lawn care companies can identify and treat the underlying causes of slime mold, preventing it from recurring in the future. This can save you money on costly treatments and repairs down the road.

Overall, hiring a professional to remove and prevent slime mold on your grass can be a smart investment. With their expertise, equipment, and experience, they can quickly and effectively rid your lawn of this unsightly and potentially harmful fungus.


In conclusion, slime mold is a common occurrence on lawns and is generally regarded as harmless to grass and plants. However, it may cause concern when it suddenly appears as white, gray, or purplish spore masses on the blades. Slime molds are not parasitic on grass but feed on other microorganisms, such as other fungi and bacteria in the soil and thatch.

While slime mold is not harmful to grass, the prevailing conditions may favor other harmful fungal infestations that may require further control response. It is recommended to maintain proper lawn care practices, such as mowing at the appropriate height, watering deeply but infrequently, and avoiding over-fertilization, to prevent the growth of harmful fungi.

If slime mold is present on the lawn, it is best to leave it alone and allow it to run its course. It will eventually disappear on its own, usually within a few days to a week. However, if the appearance of slime mold is causing concern, it can be removed by gently raking or mowing the affected area. It is important to note that removing slime mold will not prevent its reappearance in the future.

Overall, while slime mold may be unsightly, it is not a cause for alarm and does not require extensive treatment. By maintaining proper lawn care practices and allowing slime mold to run its course, homeowners can ensure a healthy and beautiful lawn.

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