Plant Diseases in Lawns

Anthracnose (Colletotrichum cereale)

• Anthracnose occurs west of the Cascade Range.
• It affects lawns with annual bluegrass. It also affects red fescue and bentgrass.
• Anthracnose develops on grasses under stress, especially when soil is dry and leaves are wet.
• Warm, humid summer weather favors its spread.

How to Identify Anthracnose

• During the summer (leaf blight phase), yellow-to-brown lesions appear on older leaves and sheaths. Later, black fruiting bodies appear. Irregular brown-to-yellow-tan to gray areas (right photo) then appear on the lawn. They range from a few inches to several feet in diameter.
• During fall and winter (basal stem rot phase, left photo), the disease rots the base of grass plants. Older leaves turn yellow at the tips, then turn bright orange-red. Damaged areas are less than an inch in diameter.

Dollar Spot (Clarireedia homoeocarpa)

• Dollar spot occurs east of the Cascade Range.
• This is a common disease on bentgrass lawn species when fertility is low.
• Dollar spot occurs in fall when the days are warm and nights are cool; also when leaves are wet for a long time and soil is dry.

How to Identify Dollar Spot

• It forms small, roughly circular, bleached patches from a few inches to 6 inches or more in diameter (left photo).
• Spots may merge into large, irregular dead areas.
• Light-yellow to tan lesions with reddish-brown borders extend across the leaf blade (right photo).
• Leaf tips may die back. They may wilt and turn tan to brown.

Leaf Spot (Drechslera spp.)

• Leaf spot occurs west of the Cascade Range.
• It is common on Kentucky bluegrass lawns.
• Leaf spot also affects under- or over-fertilized perennial ryegrass lawns.
• It occurs in cooler months.
• Symptoms are worse when grasses are mowed short.

How to Identify Leaf Spot

• Tiny, water-soaked lesions turn purple with straw-colored centers (right photo).
• Lesions may girdle the leaves (left photo).
• The lawn turns brown and thin. It looks drought-stressed.

Microdochium Patch / Pink Snow Mold / Fusarium Patch (Monographella nivalis)

• Michrodochium patch occurs west of the Cascade Range.
• It affects annual bluegrass, tall fescue, and bentgrass.
• Fine fescues, bluegrass, and ryegrass may also be infected.
• Michrodochium patch develops in cold weather (under 60 degrees Farenheit) on over-fertilized lawns.
• Damage occurs in early spring.

How to Identify Microdochium Patch

• The reddish-brown circular patches are 1–2 inches in diameter (right photo).
• The center is generally tan. It may contain uninjured grass.
• White or pinkish fungal growth may be visible at the leading edge of the patches (left photo).
• It may grow beneath the snow or as snow melts.

Tips to Get Rid of Microdochium Patch

• Rake and remove tree leaves from the lawn before winter.
• Continue to cut grass until the fall. Mow with a mulching mower or remove clippings.

Necrotic Ringspot (Ophiosphaerella korrae)

• Necrotic ringspot occurs east of the Cascade Range.
• It affects Kentucky bluegrass and fine fescue when thatch is excessive.
• Infection occurs in the fall. Symptoms become visible in summer.
• It usually occurs on 2- to 5-year-old lawns grown from sod.

How to Identify Necrotic Ringspot

• It forms circular, yellowed areas 2 to 5 inches wide, with reddish-brown margins (left photo). Patches may expand to several feet across.
• Infected patches lift easily from the soil.
• Dead rings may have green grass in the center.
• Roots and rhizomes are blackened as shown in the photo (right).

Tips to Get Rid of Necrotic Ringspot

• Don’t apply excessive organic matter such as compost.
• Annual core aeration and dethatching are recommended for susceptible grass types.
• Avoid over-watering in the fall.
• If symptoms are seen in summer, water lightly and frequently. This method will help grass grow with a damaged root system.

Net Blotch (Pyrenophora dictyoides)

• Net blotch occurs west of the Cascade Range.
• It affects tall and fine fescues, and perennial and annual ryegrasses.
• It occurs in winter when fertility is low.
• Symptoms are most severe on young grass in wet, shady areas.

How to Identify Net Blotch

• When net blotch affects fine fescue, you’ll see small, reddish-brown spots, dieback from the tip, and small brown patches of dead foliage in turf (left photo).
• In tall fescue and perennial ryegrass, net blotch creates short brown streaks in a net-like pattern on leaves (right photo).
• Heavily infected stands turn yellow and then brown.

Red Thread (Laetisaria fuciformis)

• Red thread occurs west of the Cascade Range.
• Red thread is the most common disease on perennial ryegrass. It also occurs on red and Chewings fescue. The symptoms are less severe on bentgrass. Hard fescue is resistant.
• Symptoms are most severe on lawns low in vigor and when nitrogen fertilizer is limited.
• The disease is cosmetic. It rarely kills grasses.

How to Identify Red Thread

• It forms circular or irregular yellow patches, 2–24 inches across (left photo). Bleached or tan grass tips are mixed with healthy grass.
• Fine pinkish to red fungal threads grow from leaf tips.
• Red thread grows small pink or red antler-like structures on leaf blades (right photo).

Rust (Puccinia spp. and Uromyces spp.)

• Rust is common east of the Cascade Range.
• Rust is common on Kentucky bluegrass. It also affects ryegrasses and fine fescues.
• It occurs in the fall when a lawn is under-fertilized.
• Rust is most severe when grasses are stressed.

How to Identify Rust

• Affected turf areas may be colored reddish, brown, or yellow (right photo).
• Yellow specks form on leaf blades. They turn into yellow, orange, orange-brown, or red pustules (left photo).
• Infection may also occur on stems and leaf sheaths.
• Severe rust infections can kill leaf blades.

Take-all Patch (Gaeumannomyces graminis var. graminis)

• Take-all patch occurs east of the Cascade Range.
• It is common on bentgrass species.
• It occurs when fertility is low.
• Take-all patch is most severe on young plantings in sandy soils.
• It spreads in wet weather.

How to Identify Take-all Patch

• Small circular patches appear in late spring.
• Patches are reddish brown at first, then brown to gray.
• They may enlarge to 3 feet or more in diameter over a period of years (left photo).
• Both shoots and roots are damaged (photo right).
• Weeds and annual bluegrass may grow in the center of the dead circle.

Typhula Blight (Gray Snow Mold) (Typhula spp.)

• Typhula blight occurs east of the Cascade Range.
• It develops when grass is covered by snow for more than 60–90 days.
• It occurs on lawns with heavy thatch layer.
• Damage is worse under snow on unfrozen ground.

How to Identify Typhula Blight

• Small circular, yellow to yellow-brown spots appear after snow is gone (left photo).
• Spots may reach 12 inches if snow cover lasts a long time.
• A fluffy white-to-gray mass of fungal growth may form a halo at the margin (right photo).
• It affects grass leaves and does not kill the base of grass plants.
• Grasses are able to grow back to a normal appearance.

Tips to Get Rid of Typhula Blight

• Rake and remove tree leaves from the lawn before snowfall.
• Continue to cut grass until snowfall. Remove clippings.
• Avoid compaction of snow. Remove snow from disease-prone areas in the spring, if needed.

Algae (Symploca spp. and Oscillatoria spp.)

• Algae occurs in coastal regions of the Pacific Northwest.
• It grows where growing conditions are poor for lawns.
• Shade, poor drainage, poor air movement, and compacted soils are factors that favor algae growth.

How to Identify Algae

• Greenish to black scum occurs on the soil surface and plant crowns. It may resemble an oil spot.
• The algal scum dries to a black, water-repellent crust.

Root-Knot Nematodes (Meloidogyne naasi)

• Nematodes suck sap from the root.
• They leave wounds through which parasitic fungi enter.

How to Identify Nematodes

• Infected grasses lack vigor and may be discolored, stunted, or thin.
• Grasses may have darkened, rotted roots, and yellowish areas as shown in the photo.
• Grasses may wilt and die in irregular patches.
• Nematode-infected grasses don’t respond to fertilizer, fungicides, or irrigation.

Tip to Get Rid of Root-Knot Nematodes

• Reduce plant stress from soil compaction and low pH. Improve lawn-growing conditions.

Slime Molds

• Slime molds are non-parasitic fungi that use grass blades as a support.
• They often appear suddenly.
• Slime molds appear in wet weather and when there is heavy leaf litter in the lawn.

How to Identify Slime Molds

• Slime molds are globular structures that form on grass blades.
• Slime molds vary in color from orange (shown in photo) to white/gray to purple/brown.
• Their reproductive structures break and release many spores.
• Slime molds don’t harm grasses in lawns.

What to Do About Slime Molds

• Slime molds will disappear if left alone.
• Remove small slime molds by mowing, raking, or washing.
• Remove larger masses with a shovel or a strong stream of water.

Yellow Spot (Blue-green algae) Oscillatoria spp. or Phormidium spp.)

• Yellow spot occurs on annual bluegrass and low-mowed bermudagrass.
• Drought stress, low fertility, use of organic fertilizers, low mowing, and shade are factors that favor the growth of yellow spot.

How to Identify Yellow Spot

• Small yellow spots can expand to cover large areas. Growth appears normal, aside from yellow color (shown in the photo).
• Severe symptoms can result in large declining areas of lawn.
• Algal scum occurs on the surface of the thatch.