Fusarium Patch Explained: What Every Lawn Owner Should Know

The arrival of cool, wet weather should be a time of relief for your lawn, but discovering odd-looking circular patches can be incredibly worrying. These spots are often the first sign of Fusarium patch, a frustrating turf disease that thrives in chilly, damp conditions. It can quickly spoil the look of a beautiful lawn, but don’t despair. This guide is here to help you understand what causes this disease, how to spot it early, and the best ways to manage and prevent it, ensuring your lawn stays healthy and green.

What is a Fusarium patch & why is it a problem for turfgrass?

Fusarium patch, also known in colder climates as pink snow mold, is a common turfgrass disease caused by the fungus Microdochium nivale. It is most active during cool, wet periods in the fall, winter, and spring.

The disease primarily targets cool-season grasses, with bentgrass and annual bluegrass being particularly susceptible. This makes it a significant issue for golf course greens and high-maintenance lawns.

The problem with the Fusarium patch is threefold. First, it causes significant aesthetic damage, creating unsightly patches that ruin the uniform appearance of a lawn. Second, on sports turf, it can negatively impact playability by creating uneven surfaces. Finally, if the infection is severe, it can lead to costly and time-consuming restoration efforts to re-establish the damaged turf.

What causes Fusarium patch in lawns?

Fusarium patch outbreaks are driven by a specific combination of a fungal pathogen and favorable environmental conditions. Understanding these causes is the first step toward effective prevention.

• The Pathogen: The disease is caused by the fungus Microdochium nivale. This fungus is naturally present in most soils and thatch layers, waiting for the right conditions to become active.
• Environmental triggers: It thrives in cool, wet weather, with air temperatures between 0–15°C (32–59°F). Prolonged periods of leaf wetness from rain, dew, fog, or melting snow create the perfect environment for the fungus to grow and infect grass blades.
• Lawn conditions: Certain lawn care practices can make an outbreak more likely. These include poor drainage, excessive thatch, compacted soil, and high nitrogen levels from late-season fertilization, which promotes lush growth that is more susceptible to infection.

What are the key symptoms to look for?

Identifying a Fusarium patch is relatively straightforward if you know the specific signs. The symptoms are most noticeable in the early morning when the grass is wet.

• Circular patches: The disease begins as small, water-soaked, circular patches, typically ranging from 5 to 20 cm (2 to 8 inches) in diameter. Over time, these patches can expand and merge, forming large, irregular areas of blighted turf.
• Pink or reddish margins: In active infections, especially in cool, moist conditions, the outer edge of the patches may have a distinctive pink, reddish, or brownish ring. This is a key diagnostic feature.
• Matted, slimy grass: The grass blades within the patches often become matted together and can feel slimy or greasy when wet. As the grass dies, it turns from a reddish-brown to a tan or straw color.
• Distinction from gray snow mold: Fusarium patch (pink snow mold) is often confused with gray snow mold. The key difference is the color of the fungal growth and the presence of sclerotia (small, hard resting bodies). Gray snow mold produces a whitish-gray mold and visible black sclerotia on the grass blades, while Fusarium patch has a pinkish hue and no sclerotia.

Early signs of Microdochium (Fusarium) show as small yellow, orange, or reddish spots (A). In later stages, patches develop a dark brown to black ring (B, C) with collapsed turf in the center. Close-up on seashore paspalum (D) from a Griffin, GA trial. Microdochium patch also seen on semi-dormant seashore paspalum (E) and bermudagrass (F).

How can you prevent Fusarium patch?

A proactive approach based on good cultural practices is the best way to prevent Fusarium patch from taking hold.

Prevention method	Action steps
Fertilization management	Avoid applying high-nitrogen fertilizers in late fall. Use a balanced or low-nitrogen, slow-release formula for the final application of the season.
Improve drainage	Aerate the lawn annually to reduce soil compaction and improve water infiltration. Address any low spots where water tends to collect.
Thatch control	Dethatch the lawn if the thatch layer is thicker than 1.25 cm (1/2 inch) to reduce the habitat for the fungus.
Air circulation	Prune low-hanging tree branches and shrubs to improve airflow and sunlight exposure, which helps the turf dry faster.
Mowing practices	Continue to mow the lawn at a regular height as long as it is growing to prevent a long, dense canopy that traps moisture.
Dew removal	On high-value turf like golf greens, dragging a hose or using a turf brush to remove morning dew can help reduce leaf wetness.

What are the treatment options if a Fusarium patch is already present?

If you already see signs of a Fusarium patch, you need to act to minimize the damage and prevent its spread.

• Fungicide applications: Preventative fungicide applications in the fall, before the first significant snowfall, are the most effective chemical control. If the disease is already active, curative fungicides can be applied, but they are generally less effective. Always choose a product labeled for Fusarium patch and follow the instructions carefully.
• Debris removal: Remove and dispose of any infected debris and fallen leaves, as these can harbor the fungus.
• Light raking: Gently rake the affected areas to stand the matted grass blades up. This helps improve airflow and allows the turf surface to dry out more quickly, which can slow the progression of the disease.

Conclusion

In the end, protecting your lawn from Fusarium patch is all about creating a healthy, resilient turf that can withstand the challenges of cool, wet weather. By being observant and proactive, you can keep this disease from spoiling your beautiful green space. 

For a modern assist, the Planteyes app is an excellent tool for helping you identify lawn diseases from a simple photo. Plus, you can use its in-app chat to get personalized advice from a lawn care expert, giving you the confidence to take the right action. Download it today and give your lawn the expert care it deserves.

FAQs