How Can I Recognize If My Lawn Has Any Diseases?

Does the turf have any brown circular patches on it?

Does your lawn have tan or straw-colored spots on it?

Does your lawn have green spots outlined with brown?

Have reddish-brown, tan or yellow patches developed on your lawn?

Do the grass blades have dark spots?

Are the patches of grass in your lawn water-soaked and blackened?

Does your lawn have circular, scorched patches or pink, gelatinous masses on it?

Have the grass blades developed yellow-red, powdery blisters on them?

Brown patch is a fungal disease that causes circular areas of grass up to 2 inches in diameter to turn brown and die. It tends to attack St. Augustine grass, bentgrass, bermudagrass, zoysia grass, tall fescues and ryegrasses. Control the disease by reducing nitrogen fertilization, mowing less frequently, aerating and dethatching. Top-dress with humus-building material. Water less frequently and only during the day so grass dries off quickly.

Dollar spot is a fungal disease that causes tan or straw-colored spots the size of silver dollars to appear on the lawn. The fungus occurs widely on golf greens, but may also be a severe problem on low-nitrogen, poorly drained lawns. Aerate the soil and improve drainage by top-dressing with organic matter. In the meantime, keep soil well-watered. Apply a high-nitrogen fertilizer or seaweed extract.

Fairy ring is a fungal disease that causes green circular areas that seem to grow more rapidly than the rest of the lawn. A circle of mushrooms usually develops around the edge of the infected area. Rake and discard the mushrooms as they appear. Spike the area with a spading fork every day. Water well. Encourage beneficial soil microbes by top-dressing with finished compost or organic lawn fertilizer. Eradicate the fungus by digging out the soil in the area of the ring.

The fungal disease Fusarium blight often causes problems on Kentucky bluegrass during hot and humid weather. Dethatch and aerate the lawn. Apply 1-2 inches of water each week. Raise the mowing height in the summer. Don’t fertilize in late spring or early summer. Rake out dead grass and replant with Fusarium-resistant cultivars.

Dark spots on grass blades indicate fungal Leaf spots or Leaf blights. Several fungi that thrive in hot and humid conditions can cause these diseases. Fight leaf spots and blights by building soil fertility. Set mowing height as high as recommended for your grass mix. Don’t mow during disease outbreaks to avoid spreading the fungi. Keep soil evenly moist. Restore diseased areas by raking out diseased grass and top-dressing with finished compost.

Pythium fungi cause the disease Cottony blight that makes patches of grass black and water-soaked. In humid conditions, a cottony mold may appear. The disease usually occurs in wet, poorly drained areas that have been over-fertilized. Aerate and dethatch the lawn. Have the soil tested and correct calcium deficiency, if necessary. Reduce nitrogen fertilization, particularly in fall. Keep soil evenly moist. Maintain slightly acidic soil.

Two similar fungal diseases, Red thread and Pink patch cause these symptoms. These diseases are common on bentgrass, bluegrass, fescue and ryegrass, especially in cool, humid regions. Apply an organic fertilizer with nitrogen in readily available form, such as seaweed extract. Mow regularly to remove infected leaf tips. Water regularly and thoroughly.

Rust is a fungal disease that causes yellow-rusty red, powdery spore blisters to appear on leaf blades. Rust typically occurs in late summer on dry lawns lacking nitrogen. To avoid problems, water the lawn well in the early morning, so the grass can dry off quickly. Fertilize using seaweed extract or other nitrogen-rich fertilizer. Mow regularly. Rake out dead grass and overseed with resistant cultivars.

Several insects may cause symptoms that resemble diseases on lawns. Each of them needs a different method of control, so the best way to deal with them is to determine which insect is attacking your lawn and look for specific control strategies.