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How do I know if my lawn is suffering from a lawn disease?

Scroll down to view common diseases you will encounter and their symptoms:

Ascochyta Leaf Blight 

This disease is Ascochyta leaf blight.

NOTE: Ascochyta leaf blight can often be confused with heat stress, dollar spot, white grub damage, and the burning of the lawn by chemicals. Skilled technicians can easily identify ascochyta apart from other issues

Symptoms of ascochyta leaf blight include:

  • Symptoms of ascochyta will often occur quite rapidly.

  • Large areas of grass will turn straw-colored and appear dead.

  • Healthy leaves are interspersed with infected leaves.

  • Blades will appear bleached from the tip to about 1/3 of the way down the leaf.

  • between the bleached are and the green of the rest of the blade can be a dark brown-purple banding. Can also be white banding,or could be entirely collapsed and shriveled

  • Ascochyta will only affect leaves.

Conditions for ascochyta leaf blight.

Stretches of hot, dry weather right after a period of unusually wet soil conditions (usually a result of overwatering or large amounts of rainfall over an extended period of time. Over-cutting of lawns can exacerbate ascochyta leaf blight by giving it more open cuts to infects.

Grasses susceptible to ascochyta leaf blight:

Kentucky bluegrass, tall fescue, and perennial ryegrass.


Dollar Spot

This disease is Dollar Spot.

Symptoms of Dollar Spot include:

  • Spots of light tan with a reddish brown border.

  • Spots can go from the tip of the leaf for an inch or more.

  • Stems can be affected as well.

  • If wet, white fungus mycelium or threads can be seen on the diseased areas.

  • If not treated, spots multiply and overlap, creating large dead areas.

Conditions for Dollar Spot.

Durring stretches of moderate temperatures (55-80 degrees F), and high humidity. Presence of thatch and nitrogen deficiency increase susceptibility.

Grasses susceptible to Dollar Spot:

Kentucky bluegrass, Annual bluegrass, Italian ryegrass, redtop, red fescue, sheep fescue, as well as velvet bent grass.


Red Thread
Leaf Spot
Lawn Rust
Brown Patch

This disease is Red Thread.

Symptoms of Red Thread include:

  • Pink to red strands of fungus on leaves.

  • Affected areas tend to be circular

  • Affected areas can be small (2 inch diameter) to large (15 inches).

  • Infected leaves will first look wet/soaked, quickly die, and then turn a light tan color.


Conditions for Red Thread.

During long stretches of cool and wet weather. Especially likely if a nitrogen deficiency is present.

Grasses susceptible to Red Thread:

Bluegrass, fescue, ryegrass, and bentgrass.


This disease is Leaf Spot.

Symptoms of Leaf Spot include:

  • Overall thinning/browning of areas grass will occur.

  • Discollored spots on leafs: discoloring can be purplish, brown to dark brown, or reddish brown spots with centre of tan, white, brown, or yellowish-brown

  • Leaf blotching: tiny spots of purple or red

  • Seedlings are more susceptible

  • because crowns are roots are frequently detached in grasses infected with leaf spot, hot and windy weather can easily completely kill the plants.


Conditions for Leaf Spot.

Stretches of 50-90 Degree F with high humidity. First effects shaded areas, worst in areas that are too closely cut to the soil. Excess thatch and nitrogen deficiency increase likelihood of leaf spot.

Grasses susceptible to Leave Spot:

kntucky bluegrass, ryegrass, bentgrass, fescue.


This disease is Rust.

Rust is a disease of the slow growth of grass caused but the fungus puccinia spp.


Symptoms of Rust include:

  • Yellow/green tone from a distance.

  • Blades will have yellowish-orange pustules

  • A rust/orange color can come off on shoes, clothes, and lawn mowers from contact with highly infected grass (contact is not harmful).


Conditions for Rust:

Temperatures from 65-85 degrees F are ideal for the development of rust. Dry, hot weather, and a nitrogen deficiency, which contribute to the slowing of the growth of grass, allow for the Rust fungus to set in.

Grasses susceptible to Rust:

Bluegrases, Bermudagrass, Fescues, Zoysigrass, and rye grasses.


This disease is Pythium.

Pythium is a fungus-like organism that causes root-rot.


Symptoms of Pythium include:

  • Dark purple-green soaked leaves

  • Spots in circular or irregularly shaped spots from less than an inch to up to 8.

  • Leaves can feel slimy or greasy to the touch.

  • Patches can become quite large, overtaking lawns.

  • The disease can also appear as streaks if the pathogen is spread by streams of water or mowing equipment across the lawn.

  • The formation of mycelium, a white cotton-like substance, on top of infected areas. 


Conditions for Pythium:

Lengths of warm, humid weather in which grasses are wet for, at least, 12 straight hours. Temperatures between 65-85 degrees F are ideal for the pythium organism.


Grasses susceptible to Pythium:

Bentgrasses, bermudagrass, anual bluegrass, tall fescue and perennial ryegrass.


This disease is Brown Patch.

Brown patch is caused by a fungus called rhizoctonia


Symptoms of Brown Patch include:

  • Donut-shaped rings of tan grass.

  • Grass in center of rings is often green.

  • Grass blades will be brown, but green at the grown (the base of the blade)

  • Sometimes a white fungus will appear at the edge of the dead grass.

  • These rings of infected grass can expand from very small, to several feet wide, often blending together to create larger patches of infected grass

Conditions for Brown Patch:

Warm and humid weather, with temperatures 65-85 degrees F.

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