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Identifying Common Lawn Diseases

Lawn With Disease Fungus
What is a Fungicide?

Fungicides are chemical products homeowners and professionals can purchase to prevent and control diseases in turfgrass or other types of plants. Fungicides function to get rid of fungus that causes disease. Fungicides do not serve as a cure for the damage a fungus causes, however, it will stop the disease from spreading and help plants recover. Sod University talks about what various types of common turfgrass diseases look like and discusses frequently used fungicide terminology so that you can identify the disease you may be encountering and create a proper disease control strategy.

Understanding and recognizing what different lawn diseases look like can help you come up with a better strategy for treatment. Below are pictures and descriptions of eight common turfgrass diseases that can be found throughout homeowner lawns.

Brown Patch

When you suspect a brown patch in your lawn, some things to look for include circular patches of brown, tan, or yellow blighted grass ranging from five inches to several feet wide. The symptoms tend to vary depending on the type of grass, soil, and sunlight you have. This disease is commonly found in cool season turfgrasses during the summer. Effective active ingredients in fungicides include azoxystrobin, azoxystrobin with propiconazole, pyraclostrobin (with triticonazole), and fluoxastrobin. See the fungicide products table with active ingredients near the bottom of this blog for more details. Learn more.

Large Patch
Large Patch Fungus disease

Large patch is common throughout warm season turfgrasses. Symptoms are almost identical to those of brown patch, but large patch tends to occur during the cooler and wetter parts of spring and fall. Large patch tends to make an appearance when there is an excessive amount of nitrogen applied, poor soil drainage, over-irrigation, excessive thatch build-up, and low mowing heights. Effective active ingredients found in fungicides are similar to that of brown patch and include azoxystrobin, azoxystrobin with propiconazole, pyraclostrobin (with triticonazole) and fluoxastrobin.

Gray Leaf Spot
Grey Leaf Spot Fungus Close Up

Gray leaf spot causes significant damage to mostly St. Augustine grass and ryegrass, however, tall fescue and centipede grass can also be damaged. Physical symptoms look like leaf spots on grass blades that are tan and gray in color with a surrounding purple or brown outline of the spots. Damaged leaf tips can become hooked or twisted. This disease tends to appear in warm and humid weather such as summer and early fall. Effective active ingredients found in fungicides include azoxystrobin, azoxystrobin with propiconazole, and thiophanate-methyl. Learn more.

Dollar Spot

Dollar spot looks like sunken, circular patches that measure approximately two inches in diameter. The patches are generally brown or straw-colored and can combine overtime to create larger shapes. The infected grass blades have yellow-green lesions with reddish-brown edges. The affected roots also darken. Dollar spot commonly affects bermuda grass, however in very few instances, it can be found in zoysia grass, creeping bentgrass, tall fescue and ryegrass. Fungicides with effective active ingredients for dollar spot include one of the following: propiconazole, azoxystrobin with propiconazole or triadimefon. Learn more.

Powdery Mildew
Powdery Mildew Close Up

Powdery mildew appears as a grayish-white powdery growth on the surfaces of grass blades as demonstrated in the above image. Leaves tend to turn yellow and gradually die and is commonly found on bluegrass, tall fescue and bermuda grass. Effective fungicides contain one of the active ingredients: myclobutanil, propiconazole or triadimefon.

Pythium Blight

Pythium blight commonly appears in cool season grasses such as creeping bentgrass, annual bluegrass, rough bluegrass and perennial ryegrass. Pythium blight spreads quickly and affects the leaves and crowns, which in turn kill the grass. This turfgrass disease occurs when dew periods are longer in the summer and evening temperatures reach around 68 degrees Fahrenheit. Grass with excessive nitrogen applications becomes especially susceptible. Visual symptoms include small, circular patches of collapsed, water-soaked leaves. Infected grass dies and becomes matted. Effective fungicides contain one of the active ingredients: mefenoxam, propamocarb, cyazofamid and fluopicolide.

Snow Mold
Snow Mold On Lawn

Snow mold primarily affects cool season grasses in areas that receive snow. It is hard to observe symptoms of snow mold until the spring or when snow begins to melt. There are two types of snow mold: grey snow mold (pictured above) and pink snow mold. Once the snow melts, you will begin to notice patches in your lawn with collapsed, crusty grass blades. If the patches are white, you may have grey snow mold and if the patches are pink, you may have a pink snow mold. Effective fungicides usually contain PCNB.

Summer Patch

Summer patch looks like circular patterns or rings ranging from six inches to three feet in diameter. Infected turf is off-colored or sunken into the lawn. The outer edges of the patches are orangish-bronze. Infected grass is easily pulled from the turf and the roots, crowns and rhizomes are black and rotten. Heat, drought stress and nutrient deficiencies promote summer patch symptoms that appear during the summer. Excessive nitrogen in the spring, potassium deficiencies, poor soil drainage, over-irrigation, excessive thatch build-up and soil compaction also encourage summer patch to occur. The most effective fungicides contain one of these active ingredients: azoxystrobin, azoxystrobin + acibenzolar-S-methyl, azoxystrobin + difenoconazole, azoxystrobin + propiconazole, fluoxastrobin, menfentrifluconazole, pyraclostrobin + boscalid and pyraclostrobin + fluxapyroxad.

Preventive vs. Curative Application Rates

Preventive and curative application rates differ from one another. Fungicides are applied at preventive and curative rates—most fungicide products will say something different about the amounts you should apply. However, preventive rates will always use less product than curative rates. Most bags or bottles of fungicide product will instruct you on the amount and rate you should apply. Curative rate applications fall around using five times as much product as preventive rate applications because you are now fighting a disease that is already present in your lawn. Once you know you have a lawn disease, you will have to spend more money on product to apply at a curative rate in place of applying a small amount of product to apply preventively. This is why it is always good to go ahead and apply fungicide preventively so you don’t wind up spending more money.

Contact vs. Systemic

If you walk into just about any lawn and garden or hardware store, you will notice that there are two different types of fungicides: one being contact and one being systemic. Systemic fungicides ensure the product will suppress the fungus after infection. Contact fungicides are still useful, though. A contact fungicide kills fungus upon “contact” and lasts for about seven to ten days. This makes contact fungicides good for applying on a disease before you have identified which exact type of fungus you may have. If this step doesn’t work, move towards applying a systemic fungicide. A systemic fungicide serves as a penetrant so that the chemicals are absorbed into the “system” of the plant and can take control of a fungus after infection.

Narrow-Spectrum vs. Broad-Spectrum

The next thing you will notice upon selecting a fungicide product is that some are narrow-spectrum while some are broad-spectrum. Their names are pretty self-explanatory, though. Narrow-spectrum fungicides only work really effectively against a few specific types of fungi. Most narrow-spectrum fungicides are systemic considering that the chemicals are absorbed into the plant’s system and the disease is stopped from spreading. A broad-spectrum fungicide can be used for a wide variety of fungi. Most contact fungicides are broad-spectrum.

Fungicide Product Recommendations

Based on the common lawn diseases we have listed above, here are a few fungicide product recommendations as well as their individual active ingredients.

Be sure to check out a more detailed blog on Lawn Disease Control that discusses the disease triangle and other turfgrass disease basics. Look at our Lawn Disease Control Strategies blog to learn about some of the products and application rates we recommend now that you know more. Lastly, this blog references warm and cool season turfgrasses. If you don’t fully understand the difference, read our blog called, The Difference Between Warm and Cool Season Varieties.

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