Grass Disease and Damage: How to Identify and Treat it

Maintaining a healthy, vigorously growing lawn is the best way to prevent a severe disease outbreak in your grass. Each square foot of turf contains about 500 to 1,000 individual plants, each requiring optimum amounts of water and fertilizer, the right mowing regime, and an aerated, well-drained soil. If any of these factors are missing or in excess, the grass may become stressed and more susceptible to disease. Knowing what you which grass disease you are dealing with is the first step to transforming your grass to a healthy and flourishing turf.

Brown Patch

Appearance: Circular patches of brown grass, a few inches to several feet in diameter. Brown leaf tips and visible lesions on the blades. When the grass is cut short the patch may develop a bluish tint. Grass inside the patch can sometimes recover leaving a ring of dead grass around the outside.

Grass Types Affected: All types but usually tall fescue, perennial rye-grass, St. Augustine grass and centipede grass.

Why it happens: Hot humid weather.

How to Fix the Problem: Allow grass to dry between watering. Water deeply and infrequently early in the morning. Aerate the lawn to reduce thatch. Avoid using fertilizer that is high in Nitrogen. If Brown Patch is under trees, prune them to allow sunlight and increase air circulation to help dry out the grass.

Dollar Spot

Appearance: Bleach, straw colored grass patches 1 to 5 inches in diameter may grow together to create larger area. Hour glass shaped blotches on the blades. White cottony threads of fungus are visible on the plant in the morning.

Grass Types Affected: Mostly Kentucky Blue Grass or Bentgrass but other types can also be affected.

Why it happens: Warm days and cool nights of spring and fall. Heavy thatch, wet grass, and nitrogen deficiency.

How to Fix the Problem: Aerate to reduce thatch, fertilize to increase level of nitrogen. Water when necessary also let the grass dry out between watering. Reseed with a disease resistant grass type.

Leaf Spot

Appearance: Elongated, circular spots on the grass blades. Spots have brown centre with black to purple edges.

Grass Types Affected: Kentucky bluegrass, fescue, and Bermuda grass are most prone.

Why it happens: Overcast, cool, wet weather. Lawns that are mowed to short or improperly watered. 

How to Fix the Problem: Mow grass at highest recommended height. Cut back on watering until the weather changes. Avoid heavy nitrogen based fertilization. 

Snow Molds

Appearance: The two types are pink and grey snow mold, they show up after the snow has melted. Areas affected by pink snow mold have a pinkish mold around the edges, while grey snow mold areas have a grayish-brown fuzzy mold surrounding the dead spot.

Grass Types Affected: All grass types.

Why it happens: After snow has been on the ground for several months.

How to Fix the Problem: Avoid excessive Nitrogen applications in the fall. Mow the grass until it stops growing, longer grass is more susceptible to snow molds. Aerate and reduce thatch to improve drainage.

Powdery Mildew

Appearance: White or grayish powdery substance on the upper growth of the plant. Grass looks like it has been dusted with flower.

Grass Types Affected: All grasses especially Kentucky bluegrass.

Why it happens: Areas of the lawn without much air circulation and sunlight, especially shady areas. The high humidity and warmer temperatures of summer are perfect conditions for powdery mildew.

How to Fix the Problem: Improve air circulation and increase sunlight by pruning trees and shrubs. Plant a shade tolerant grass type in vulnerable areas. Avoid overwatering and over fertilizing in shady areas of the lawn.

Rust

Appearance: Begin as small yellow spots on leaves that develop into rust-colored patched of spores. The entire affected area has a rust colored look.

Grass Types Affected: Any grass type especially Kentucky bluegrass, ryegrass, and zoysia grass.

Why it happens: Moderately warm, moist weather and when dew stays on the grass for 10 to 20 hours per day

How to Fix the Problem: Rust won’t last on a properly maintained lawn. Fertilize, water and mow the grass properly.

Red Thread

Appearance: Grass will turn brown and strands of red threadlike patches of fungus appear at the leaf ends. Entire area will have a reddish tinge.

Grass Types Affected: Fine fescue, perennial ryegrass are most susceptible, but Kentucky bluegrass, bentgrass, and Bermuda grass may also develop the disease.

Why it happens: Cool, moist weather.

How to Fix the Problem: Maintain balance nitrogen and pH levels.

Fusarium Blight

Appearance: Starts as scattered, small circular spots of dead grass. The grass turns dull tan to reddish brown. The patches will enlarge and live green grass will start to grow in the middle of the patch create a ring of dead grass.

Grass Types Affected: Mainly drought-stressed Kentucky bluegrass but also Perenial ryegrass, bentgrass, and tall fescue.

Why it happens: Hot, dry, windy weather. Lawns with shallow root system from incorrect watering are very susceptible.

How to Fix the Problem: Aerate to control thatch. Improve watering practices. Apply Nitrogen fertilizer. Mow at the correct height and reseed.

Pythium Blight

Appearance: Small areas of grass turn light to reddish brown and die. These areas often look water soaked or slimy when wet. White cottony fungus can be seen on the blades of damaged grass in the early morning.

Grass Types Affected: All grass types.

Why it happens: Warm humid weather. Lawns with a soil pH. Pythium blight is carried by lawn equipment and water run-off.

How to Fix the Problem: Aerate to reduce thatch and increase water penetration. Test the soil and correct any alkalinity imbalance. Water in the morning and avoid mowing wet grass.

Stripe Smut

Appearance: Grass blades turn pale green to yellow. Spores form stripe on the blade, turning gray to black. The leaves curl, appear shredded at the end and die. Grass in diseased areas grow slower than healthy areas.

Grass Types Affected: All grass types.

Why it happens: Most active in cooler weather of spring and fall then the damaged plants die in summer

How to Fix the Problem: Avoid overwatering and follow a regular fertilization program. Reduce excessive thatch buildup.