Snow Mold on Grass | Treating Pink Snow Mold on Lawn

Keith Hardy - Bio Photo
Keith Hardy
Senior Editor

Keith has been involved in the gardening and landscaping industry for the past 21 years. From a jobbing gardener to running his own landscaping services....

The winter months are very important for the health of your lawn. Snow mold on grass is something that you don’t want to happen. Snow mold, in fact, is an overarching term that covers two different lawn infections gray snow mold and pink snow mold (fusarium patch) These lawn diseases generally occur during the winter and spring seasons.

Snow mold grows on snow or frost and then moves to grass blades. It causes brown or purple patches or pink circles depending on the infection and in some cases grasses, particularly in the case of pink snow mold, even die. Furthermore, pink snow mold is capable of existing unseen throughout the summer months and thus this fungus has the potential to do long-term damage to your grass.

What is Snow Mold on Grass?

Snow molds are fungal diseases that thrive under snow causing damage to grass. They can occur at any time but are generally more noticeable after periods of standing snow. Depending on the variety they can be one of the most damaging diseases for turfgrasses and can be difficult to control. It is found most frequently during autumn, winter, and early spring, but attacks can occur at any time of the year. If they take hold they can be very destructive and they may be very difficult to treat once established.

There are two distinct varieties pink snow mold and gray snow mold. The pink variety is more common than the grey one. It usually occurs in the late winter months when a covering of snow seals in heat and moisture underneath it, producing a perfect environment for fungal growth to flourish.

This kind of snow mold (Microdochium nivale), which is also referred as microdochium patch tends to do more harm than its grey cousin since it may also kill grassroots and crowns, rather than simply the blades, as it grows. Furthermore, since it is capable of living unseen throughout the summer months, this illness has the potential to do long-term damage to your grass.

What causes snow mold on grass?

Snow mold on grass can come in two distinct variations, gray snow mold caused by the Typhula pathogen and pink snow mold caused by Microdochium nivale pathogen. These two fungi are incredibly resilient and can survive in temperatures as low as -5 degrees Fahrenheit but is at their most active between 32 and 60 degrees Fahrenheit, depending on the variety. The fungi thrive in wet conditions, especially where snow has insulated wet grass for a prolonged period.

Gray Snow Mold

What causes snow mold on grass? gray snow mold

Typhula incarnata or other Typhula species are responsible for the development of grey snow mold. Right after the snow melts, circular areas of the injured lawn may be seen in various shades of yellow to white.

Patch sizes range from small to broad, and they may overlap to wreak havoc on huge sections of lawn. Sclerotia (yellowish fibers) are produced by the fungus and grow to a dark-brown to black hue when fully matured. These fibers are plainly apparent and remain throughout the summer and into the late autumn. After the standing snow cover has melted away, these fibers spread and begin colonizing grass blades again about four to six weeks later.

Gray snow mold infections usually happen most during the winter and or early spring months. The ideal temperature for the fungi to thrive is between 32 and 40 degrees Fahrenheit. Gray snow mold infections very seldom cause the grass to die, thus treatment is not always necessary. 

Pink Snow Mold

What causes snow mold on grass? -pink snow mold

Pink snow mold can be more problematic as it is a far more destructive infection than gray snow mold because it attacks the roots as well as the grass blade. This fungus, however, is active in a much narrower temperature range between 32-60 degrees F. and in moist circumstances.

The pink snow mold variety is produced by the fungus Microdochium nivale, which creates broadly circular-shaped bleached patches varying in size from one to six inches in diameter. Initially, the patch will seem reddish and water-soaked, but it will eventually become a pinkish-white color with a reddish border as the water evaporates. 

Grass Susceptible to Snow Mold

Snow mold is most often seen in cool-season grasses, which are more sensitive to the disease. It particularly affects grass species such as annual meadow grass, but it may also be problematic on some types of bentgrasses, fescues, and perennial ryegrass.

The presence of snow mold fungus is associated with the capacity of most species to withstand freezing temperatures and ice cover. In order for a grass plant to be properly acclimated and ready for the winter, it must have stopped growing, stored some extra sugar for the winter, produced anti-freeze proteins within its cells, and modified its cells’ membranes to make them more stable when subjected to freezing and thawing conditions.

Warm temperatures throughout the winter might cause the lawn to trigger de-acclimatization causing infection. The degree to which turfgrass species are vulnerable to such warm periods varies from one species to the next.

The following grass species have a better genetic resistance to both gray and pink snow mold than other turfgrasses. Browntop (Colonial bent), Chewings red fescue, and Velvet bentgrass. Whilst none of these grasses are completely immune to snow patch they have a much better they are most winter stress-resistant grass varieties available. 

How to Control Snow Mold

The treatments used to cure the harm caused by these two forms of mold are substantially different in the spring. Pink Snow mold may have to be treated with a fungicide (see below) if the affected area is large enough. When dealing with Gray Snow Mold, carefully rake the afflicted portions of the grass to aid drying and prevent future development. It is not usually suggested to use fungicides. It is possible that some reseeding may be required to fill up areas that have been severely damaged.

Treating Pink Snow Mold on Lawn

Treatments with fungicides may be required to control pink snow mold on newly planted lawns or on lawns that have already had mold infestations.

Chemical control | Snow mold fungicide

Lawn Fungicide | Using the Correct Treatment to Combat Lawn Disease

The most common fungicide used to treat snow mold infections is trifloxystrobin. The fungicide may be applied throughout the year, with the exception of when the grass is frozen or when there is a drought. Because there is a possibility of resistance developing in the fungal population, the product should not be sprayed more than twice a year and should be used in combination with other control measures whenever possible.

Other fungicides that are used contain chlorothalonil, fluazinam, and mancozeb. In certain states and countries, these may be limited to only professional applications. Your local garden center should be able to advise.

Nonchemical control

Improve lawn aeration and drainage to ensure that the grass dries out quickly after dew or rains. To help this process, a mix of scarifying, spiking, and hollow- or solid tining may be used.

In addition, by trimming down overhanging trees or bushes, you may improve the overall airflow across your lawn helping the drying out process. If there is a particularly heavy dew this should be removed first thing in the morning using a switch (a long, bendable rod) or a bamboo cane.

Finally, you should avoid using excessive dosages of nitrogen fertilizer in the late summer or fall – instead, might be preferable to use a special autumn lawn feed designed specifically for your grass.

Prevention of Snow Mold Disease

Prevention of Snow Mold Disease

Prevention is always preferable to having to cure a problem like snow mold. Unfortunately, it is impossible to completely eliminate the possibility of snow mold infections but you can take numerous steps to ensure that it is less likely

Cultivation practices, cultivar selection, and garden cleanliness should be the primary lines of defense against snow mold fungus. your lawn care maintenance program is the best place to start.

Due to the fact that taller grass tends to mat more easily when coated in snow, pink snow mold is more frequent in grasses that are two inches or more in height. The best course of action is to maintain a healthy lawn and maintain regular mowing well into the fall months. It is advisable that the last cut of your lawn before winter leaves the grass short.

Snow mold often affects areas, where the soil is very compact good aeration of the lawn, especially in these areas, can be very important. This can be done with a garden fork or can be done with aerators either solid or hollow tines.

Reducing thatch is also an important element in allowing the grass the breath. Mulch and leaves laid down in thick layers provide the ideal setting for the growth of pink snow mold. This can be done by scarifying your lawn.

If you are planning to reseed parts of your lawn consider reseeding with more fungi-resistant grass species and turfgrass varieties.

It is also important to keep an eye on the nitrogen levels in your soil. Too little can result in other lawn fungi such as dollar spot and red thread taking hold, too much can cause snow patch becoming a problem

There are other sensible steps that you can take including not exacerbating the infection by not properly cleaning your garden tools. During the foliar blight stage, mowing unfortunately is a very efficient way of spreading this fungus across the field. If you are using a professional lawn care company ensure they have properly cleaned their equipment and that you don’t suffer cross infections from other jobs.

Finally, if you do experience snowfall try to avoid piling the snow into mounds on the grass if you are clearing pathways or drives.

Keith Hardy - Bio Photo
Keith HardySenior Editor

Keith has been involved in the gardening and landscaping industry for the past 21 years. From a jobbing gardener to running his own landscaping services. He is now dedicated to bringing you the latest in gardening news. Read more

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