How to Deal with Gray Leaf Spot on Your Lawn

If you’ve noticed that your once vibrant lawn has lost its luster, it’s likely because it’s being attacked by a pesky fungal disease. Gray leaf spot, scientifically known as Pyricularia grisea, is one of the many lawn diseases that homeowners should be aware of. This fungal infection manifests as oblong spots on the grass leaves, and if left untreated, it can wreak havoc on your entire lawn, especially if it’s newly established. In this article, we’ll delve into how you can identify and effectively treat gray leaf spot using the right techniques and fungicides.

Recognizing Gray Leaf Spot

The first and most distinctive symptom of gray leaf spot is the appearance of round or oval spots on the surface of the grass blades. These spots usually have a tan color with a dark brown border. In high humidity or wet conditions, the spots will turn gray and fuzzy, with increased sporulation growth. If left unchecked, the disease will spread across the entire leaf, leading to the death of the affected plants.

Understanding the Causes

Gray leaf spot is caused by the fungus Pyricularia grisea, which infects and kills the leaf blades of turfgrass. Temperature plays a crucial role in the occurrence of this disease, as it requires a range between 70 and 95 degrees Fahrenheit to thrive. Additionally, the fungus requires at least 14 hours of continuous leaf wetness. Improper irrigation, cloud cover, shade, or excessive rainfall can exacerbate the condition.

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Seasonal Impact

Gray leaf spot is commonly found in newly-established lawns, particularly during their first year of establishment. It poses the most significant threat during this period, potentially damaging entire lawns. As the turf matures, the disease becomes less damaging but can still cause issues. Therefore, it is important to properly manage and control gray leaf spot using cultural or chemical methods. The timing of gray leaf spot varies depending on the type of grass. For St. Augustine turfs, it is most active from June through August, while perennial ryegrass and tall fescue are mainly affected from late July through September.

Grass Types Affected

Although gray leaf spot primarily affects St. Augustine grass, it can occasionally be spotted on other grass types such as tall fescue, perennial ryegrass, bermuda grass, and centipede grass. The severity of gray leaf spot varies depending on the grass species. St. Augustine grass is more resistant to the fungus, while perennial ryegrass is highly susceptible and can die within days. Other grass types, like tall fescue, have an intermediate level of resistance.

Cultural Control Techniques

Implementing preventive measures can help hinder the development of gray leaf spot. These measures include reducing the thatch layer, using the appropriate fertilizer, and mowing at the proper height. Deep and infrequent watering can also prevent continuous leaf wetness, which is favorable for gray leaf spot. If the disease is already present, these cultural control techniques may effectively eliminate it. However, in most cases, fungicide applications are the best option for controlling gray leaf spot.

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The Role of Fertilizers

Many big box fertilization programs prescribe excessive amounts of nitrogen, which can lead to fungus outbreaks. It’s crucial to provide your lawn with nitrogen, but in moderate quantities. Slow-release nitrogen fertilizers ensure a controlled release over an extended period, preventing excessive nitrogen from entering the soil at once. Lawnifi® Fertilization Program is recommended as it supplies your lawn with the required nutrients in nano-sized form, precisely when it needs them, through easy monthly applications from March to November. This approach reduces the risk of fungus outbreaks while maintaining lawn health.

Chemical Control Options

When it comes to fungicides for gray leaf spot, there are several products to consider. Azoxystrobin, chlorothalonil, fluoxastrobin, and propiconazole are a few fungicides known to effectively control this disease. These fungicides come in various brands such as Heritage G, Fame C, and Banner MAXX. Choosing the best fungicide depends on the specific requirements of your lawn and the severity of the gray leaf spot infection.

Prevention is Key

Apart from using disease control products to fix gray leaf spot, preventive measures can also be taken to avoid its occurrence in the first place. Applying one of the aforementioned products at a preventive rate can keep the disease at bay. Always follow the instructions on the product labels when applying fungicides, and consider rotating between different chemical classes to prevent fungicide resistance.

Keeping a Watchful Eye

Regardless of whether you’re trying to prevent or treat gray leaf spot, closely monitoring your lawn is crucial. By employing the right maintenance practices, you can promote healthy growth throughout the season, resulting in a beautiful and flourishing lawn.

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For more information and expert assistance, visit the Ames Farm Center website.