What Are Some Causes of Lawn Damage?
Foliar and root diseases can affect both warm- and cool-season grasses. Disease-causing fungi are almost always present in the soil, waiting for a time when conditions are right to attack. The most common times are when the host (turfgrass) is under stress.
Examples of environmental stress are excessively wet or dry weather and exceptionally hot or unseasonably cool temperatures.
In addition to being a reaction to environmental changes, lawn diseases can also be signals of soil problems. Any part of a lawn can be affected. Slopes, depressions, high traffic and shady areas are vulnerable.
Improper mowing or watering habits, too much or too little fertilizer, thatch and compacted soil all increase the chances of disease.
Lawn Disease and Fungus
To understand lawn disease, you need to understand lawn fungus. What is lawn fungus? Lawn fungus is a pathogen made up of tiny organisms known as fungi that feed on organic matter in the grass that causes lawn disease. Most lawn diseases are caused by different types of fungi that thrive in the right environmental conditions. While there are a variety of things that can affect your lawn, diseases may not always be the culprit. Diseases often start as yellow, tan or brown areas of varying sizes in the lawn. But before you assume you have a lawn disease, make sure it isn't something else.
Injury, stress or deficiencies can produce similar symptoms and also set the stage for infection. These are often things that you can control, so it's wise to recognize and remedy these situations. Dormancy in the grass is a natural occurrence and is another factor that can cause discoloration.
Injury to Grass
Pesticide, fertilizer or gasoline spills
Spills can cause lawn damage quickly, resulting in yellow or brown spots. Refill spreaders, sprayers and outdoor power equipment carefully. Use a funnel or a "no-spill" container. You can rake up dry products and collect them for use later. Flood the area with water to dilute. You need to remove liquid spills with an absorbent product and dispose of the liquid and absorbent properly. Repair and reseed the area as needed.
Dog urine
These spots show up as a dead area with a green ring around it. Flush the area with water as soon as possible after the occurrence (within the hour is best). Work with your dog to use a less conspicuous area.
Foot traffic
Aerate to relieve soil compaction and reseed. Redirect the traffic. If that proves impossible, install a walkway.
Mowing too close
Raise the mower blade to the proper cutting height for your variety of turfgrass. Fix high spots in the lawn.
Dull mower blade
A mower blade that is not properly sharp can produce a ragged cut and discoloration. Replace or sharpen the blade according to the manufacturer's instructions to prevent ongoing damage.
Compacted soil
Aerate to relieve soil compaction. Add organic matter and reseed.
Grass Stress
Too much or too little water
If the lawn is not getting enough water, the turfgrass begins to resemble straw. Walking on the lawn leaves footprints in the turf. Water only when needed to prevent overwatering. Do it as early in the day as possible to allow evaporation from grass blades. Be sure to follow any watering ordinances or restrictions for your area.
Too much or too little fertilizer
Too much fertilizer causes excessive growth. Too little does not provide enough nutrition to promote the strong roots, crowns and leaves needed to withstand disease. Follow the proper feeding schedule for your turfgrass.
Excessive pesticide use
Applying too much insecticide or herbicide can "burn" turfgrass and lead to yellow or brown grass. Follow the manufacturer's specifications on amount and frequency of application.
Hot and cold temperature extremes
Wait for a change in the weather. Keep your eyes open for early signals of lawn problems.
Nutrient Deficiencies in Grass
Nitrogen
Lawns that are not getting enough nitrogen (the key component of lawn fertilizer) will begin to change to light green and then yellow. The color change usually begins to show first in the lower leaves. Reduced growth is also a sign of nitrogen deficiency. Normally the entire lawn is affected. Adding nitrogen will help restore the green color if you fertilize properly. Applying too much at the wrong time can do more harm than good. Follow the package instructions carefully. Grass cycling - leaving grass clippings on your lawn after mowing - adds nitrogen naturally to the lawn.
Iron
Another reason for discoloration could be lack of iron in your soil. Some of the more common areas of the yard that you might find turning yellow from iron deficiency are those adjacent to things made of concrete. Driveways, sidewalks and concrete planters can be the culprits. The high alkaline content in concrete tends to absorb the iron found in soil, reducing the amount of iron your lawn or garden receives.
Iron deficiency appears in patches. Blades may yellow but the veins retain their green color. Iron deficiency may not affect growth. Alkaline soils (such as those in the midwestern and western states) are especially susceptible to iron deficiencies. You can add iron as a soil supplement to neutralize alkalinity and help replenish the iron that occurs naturally in the soil. Apply as directed on the package. Remove the product from masonry or concrete surfaces before watering to avoid staining.
When using lawn treatments or lawn care products, always follow package directions regarding proper clothing, protective equipment, application procedures and safety precautions.
Other Lawn Conditions
In addition to injury, stress and deficiencies, there are other things that may be making your lawn look less than picture perfect.
Damping off is a fungal infection that is usually limited to newly seeded areas. When seeds are sown too densely and then receive too much fertilizer and water, the crowded young seedlings collapse and die. You'll need to rake and reseed the area.
Dormancy is a natural occurrence. Cool-season grasses will turn brown when the weather gets hot and/or dry. Warm-season grasses go dormant when cooler temperatures arrive. They will return to normal conditions when the weather changes. If dormancy occurs late in the growing season, they will remain dormant until the next growing season arrives. Before taking any type of action to solve discoloration, make sure your lawn is not turning yellow or brown because it's going dormant. Dormancy is a resting period – do not fertilize during dormancy.
Insects are another possibility. Signals are holes in the leaves and chewed-off spots. If the turf can be pulled up easily, grubs are the likely culprit (diseased grass remains firmly rooted). Other lawn-harming insects include billbugs, chinch bugs, nematodes, mole crickets, mites, leafhoppers and various larvae. Upon close examination you can see many of these bugs.
How Do You Identify Lawn Diseases?
When you have eliminated the afflictions mentioned above as possible causes of lawn discoloration, review the possibility of disease.
Warm-season grasses are most susceptible when temperatures are cooler than normal. Cool-season grasses are at risk when weather is warmer than normal. Look for other weather patterns such as excessively wet or dry weather and cloudy or overcast skies (which inhibit the ability of grass to dry out sufficiently and mean that dew is unable to evaporate). If any of these conditions prevail, then disease is likely.
Identify the problem, find the solution, control the problem and take steps to prevent future occurrences.
Watch our DIY Basics video: How Do I Use a Lawn Spreader?
How Do I Know What Kind of Lawn Disease I Have?
If you suspect a lawn disease, knowing the type of grass you have and the symptoms of different conditions will help you identify the problem. We've listed the most common lawn diseases below, along with the turfgrasses they affect, the lawn fungus that causes them, the time of year you may see them and some symptoms of each.
Anthracnose
Anthracnose is characterized by irregular-sized tan, brown or reddish brown patches of grass ranging in size from several inches to several yards. Spots may also be present on grass blades.
- Caused by the fungus Colletotrichum cereale
- Affects any turfgrass but primarily bluegrass and centipede
- Can occur in summer and fall
Brown Patch
Brown patch lawn disease appears as circular areas of dead grass that may be small or large. The outer portion may be a smoky color. The blades of grass can be easily pulled from the stem. Affected areas may have a sunken appearance. Brown patch doesn't usually cause permanent damage.
- Caused by the fungus Rhizoctonia
- Affects fescue, bluegrass, centipede, ryegrass, St. Augustine, bent grass and zoysia
- Occurs in spring and fall
Dollar Spot
Small (silver dollar-sized) spots of tan or brown grass appear over the lawn. The spots may merge into large areas. Grass blades will have tan or brown areas on them. Dollar spot doesn't usually cause permanent damage.
- Caused by the fungus Sclerotinia homeocarpa
- Affects bent grass, Bermuda grass, ryegrass, bluegrass and fescue.
- Occurs in late spring, summer and fall
Fairy Ring
Fairy ring is characterized by a dark green circle or semicircle of grass. The perimeter of the fairy ring may be a lighter area of dying grass. Mushrooms may or may not be present. The entire affected area must be dug up and reseeded.
- Caused by various underground fungi
- Affects all turfgrasses
- Occurs any time of the year
Fusarium Blight
In a lawn with fusarium blight, grass color transitions from light green to brown to tan before dying.
- Caused by the fungus Fusarium roseum
- Occurs in hot, dry weather
- Affects bluegrass
Leaf Spot
There are leaf spot infections that attack warm- and cool-season grasses. Grass begins to appear gray, tan or brown. Upon closer examination, tan, red or purple spots are evident. Leaf spot can severely thin or kill turfgrass.
- Caused by the fungus Drechslera poae
- Affects all turfgrasses
- Occurs in spring, summer and fall
Necrotic Ring Spot and Summer Patch
Necrotic ring spot appears as round, sunken areas of reddish tan grass that resemble a bull's eye.
The very similar summer patch takes a more oval or irregular shape.
- Caused by the soil-borne fungus Ophiosphaerella korari
- Affects bluegrass, bent grass, Bermuda grass and fescue
- Occurs in spring, summer and fall
Powdery Mildew
Common in shady areas, the infection resembles white dust. Blades eventually turn tan and brown. The damage can be permanent.
- Caused by the fungus Blumeria graminis
- Affects bluegrass, Bermuda grass and zoysia
- Occurs in spring, summer and fall
Pythium Blight
Pythium blight is also called grease spot due to the brown slimy areas it produces. White patches may also appear. This condition can spread and kill grass quickly.
- Caused by the fungus Pythium aphanidermatum
- Affects all turfgrasses
- Occurs in spring, summer and fall
Red Thread
You'll notice red or faded patches with reddish or pink threads reaching from leaf tips to adjoining leaves. Damage isn't usually permanent.
- Caused by the fungus Laetisaria fuciformis
- Affects fescue, bluegrass, ryegrass and bent grass
- Occurs in spring and fall
Snow Mold, Pink Snow Mold or Fusarium Patch
Snow mold usually occurs after snow melts, but it can also be caused by cold, wet weather at other times. It starts as greenish yellow but turns a distinctive pink shade.
A gray color indicates another snow mold variety that matures under snow layers during colder winters. This type starts with a yellow tint that turns grayish white.
As temperatures start to rise with the approach of spring, snow mold will likely go away on its own. If not, simply reseed the area.
- Caused by the fungus Microdochium nivale
- Affects cool-season grasses and zoysia
- Occurs in fall, winter and spring
Rust
This condition creates a distinctive orange rust-like appearance. The spores attach easily to tools and clothing. Rust isn't usually harmful.
- Caused by the fungi Puccinia coronata and Puccinia striiformis
- Affects bluegrass, Bermuda grass, St. Augustine and ryegrass
- Occurs in summer and fall
Slime Mold
In a lawn affected by slime mold, patches of white, gray or black deposits appear on leaves. Slime mold may appear powdery in early stages but it forms tiny balls as the infections mature. The condition won't cause permanent damage, but can inhibit growth if the infestation is heavy. Remove with a rake, broom or by spraying with a garden hose.
- Caused by the fungus Mucilago spp
- Affects all turfgrasses
- Occurs in summer and fall
Smut
In a lawn with smut, yellowing blades turn to black and begin to curl. The entire plant is affected and is likely to die.
- Caused by the fungus Ustilago striiformis
- Affects bluegrass and bent grass
- Occurs in spring and fall
How Can I Control Lawn Disease?
To prevent disease from spreading, remove grass clippings from infected areas. Avoid walking through the area and clean any tools you have used before they come in contact with other parts of the lawn.
Apply fungicides when needed. Make sure you choose one that's formulated for the specific disease that's affecting your lawn. Follow the manufacturer's instructions carefully.
Frequent applications of fungicide can have an adverse effect - over time, many diseases will develop a resistance to them. Spot-treat affected areas rather than the entire lawn. Alternate fungicidal products to maintain efficiency. Some fungicidal remedies can be applied only by a licensed pesticide applicator.
When using plant-care or lawn-care products, always follow package directions regarding proper clothing, protective equipment, application procedures and safety precautions.
How Can I Prevent Lawn Disease?
Short of choosing grass types that are known to be resistant to common lawn diseases, general lawn care practicescan create a healthy stand of turf. To achieve that goal:
Feed regularly, following the correct fertilizing schedule for your turfgrass type. A well-fed lawn is able to fend off disease, pests and weeds better than one that is undernourished.
Water deeply and infrequently to promote deeper root systems. Water early in the morning to allow evaporation during the day.
Mow at the correct height for your grass, as frequently as necessary to maintain that height. Mowing too short weakens the grass plant, making it more susceptible to infection. Mow often enough so that you remove no more than 1/3 the height of the grass blade at one time. Maintain your mower properly - a sharp blade prevents ragged cuts. Mow when the grass is dry and change the mowing pattern each time you mow to avoid establishing a grain.
Maintain your lawn year-round:
- Grow the proper turfgrass for your region and environment. Plant disease-resistant turfgrass varieties. Use a suitable turfgrass variety in shady areas.
- Do regular soil tests (every 3-5 years) and follow the test recommendations.
- Aerate your lawn to increase availability of oxygen, nutrients and water to the root zone. Aerating also relieves soil compaction.
- Remove thatch when it becomes over 1/2 inch thick.
- Increase sunlight or improve air circulation by thinning (but not topping) trees and shrubs.
- Eliminate low areas in your lawn. These allow water to accumulate and disease to flourish.
- Remove high spots and improve drainage in the lawn.
- Fallen leaves can provide a home for disease and pests. Keep lawns free of leaves and other debris.
Be sure to observe any watering ordinances or restrictions for your area.