Brown spots in lawns are frustrating to deal with! Just when you think you’ve done everything right, suddenly there’s a patch of grass that’s dead or dying. There are a number of causes of brown spots in lawns, from insects to disease to human error.
To get to the bottom of the situation, you’ll have to do a little old-fashioned investigating. Here’s a checklist to help you determine the cause of brown spots in your yard.
Human and Animal Damage
Unfortunately, it’s very easy for us (and our pets) to damage lawns. Some common causes of brown spots include:
Dull Mower: Dull mower blades tear your grass, causing damage and gradual death to the grass.
Remedy: Sharpen your blades in fall and spring. After mowing, examine your grass to see if the mower is cutting cleanly.
Scalping: If your mower blade is set too low or there are lumps in the lawn, it can cut the grass too short and cause damage.
Remedy: Practice proper mowing techniques by raising your mower blades, and smooth out high spots by digging up the sod, removing some of the soil underneath, and replacing the sod.
Chemicals: Gasoline, fertilizer, herbicides, and pesticides can cause dead spots if spilled. If fertilizer is applied unevenly or incorrectly, it can burn the grass. Even insect repellents can burn your lawn when sprayed on the grass blades.
Remedy: Pour chemicals, fuels, and sprays on your driveway, not on your lawn, and follow application directions.
Animal Urine: Dogs are the most common culprit, but large birds and other animals can cause urine spots, too. Urine usually causes your lawn to turn yellow in spots, sometimes with a bright green ring around the edges where the diluted nitrogen in the urine acts as a fertilizer.
Remedy: Check out our article on How to Keep Dogs From Damaging Your Lawn for tips.
Take a sample of stems, roots, and soil for analysis.
Poor Growing Conditions
The conditions in your yard may be unfavorable for grass to grow:
Poor Soil: Soil quality can vary in your lawn, and poor soil can occur in patches, causing brown, bare areas or moss.
Remedy: Take a screwdriver and push it into the soil. If it doesn’t go easily, your soil is likely compacted. Try aerating and top-dressing to incorporate organic matter in the soil. When you aerate, take a look at the plugs, to see how the quality and texture of your lawn varies in different spots. Keep this in mind as you amend and improve your soil.
Buried Debris: I once puzzled over a brown patch for weeks before finding an old piece of buried lumber under the grass.
Remedy: While you’ve got that screwdriver handy, poke around a little to see if anything is underneath the sod.
Erosion: Water tends to run off slopes, taking grass seeds and young shoots with it, and leaving bare ground or dried out areas behind.
Remedy: Aerate your lawn to increase water absorption. If the slope is steep, consider building terraces or planting groundcover.
Roots: Large trees or shrubs usually win the battle for water and nutrients. The area under trees is notoriously difficult for growing grass.
Drought: Lawns need one inch of water per week, either from rainfall or irrigation. Dry, compacted spots are more easily drought-damaged.
Remedy: Keep an eye on dry, sunny spots, especially if your soil drains poorly. If you irrigate, make sure your entire lawn is watered evenly.
Dormancy: Cool-season lawns can go dormant during the heat of summer while warm-season lawns go dormant during the winter. If your lawn has a mix of grasses, you’ll have curious brown patches as some areas go dormant while others stay green.
Remedy: Seasonal dormancy is normal, but make sure your lawn is healthy and strong to prevent unnecessary browning.
Brown spots caused by dormant Bermuda grass mixed with green fescue.
Common Lawn Diseases and Pests
If you’ve eliminated all the above causes, it’s time to move on to some of the more serious diseases and pests that plague lawn grasses. Some of the most common culprits are:
Thatch: Thatch is a buildup of decaying grass blades that can build up so thick that it chokes out healthy grass.
Remedy: Remove thatch if it is more than ½” thick.
Grubs: Grubs are a common problem in mid to late summer, and most easily identified when your sod easily pulls back from the ground like a carpet.
Remedy: Pull back a section of sod and inspect for fat, white curved worms. More than ten per square foot can cause lawn damage. Grub control products are available at your garden center.
Chinch bugs: Chinch bugs are a common summer pest in warm-season lawns, especially in hot sunny patches beside driveways and sidewalks.
Remedy: Inspect your lawn closely, and look at your shoes as you walk through the grass – you should be able to spot the small black and white adults. They’re resistant to many pesticides, but there are products available to target them.
Other insects: Caterpillars and other pests can live part of their life cycle in lawns.
Remedy: Watch your lawn closely – look for crawling and munching insects and for grass blades that look eaten. Also watch for birds and wasps feeding on these pests in your lawn.
Fungal Diseases: Brown patch and other fungal diseases thrive in moist conditions, most often in midsummer (when nights and days are hot and humid) and spring (as snow melts). They may show up as circular or irregular brown spots, or you may notice a spotting or infected pattern on the blades or a generally dying/thinning out.
Remedy: Increase air circulation and sunlight as much as you can, to make your lawn less inviting to fungus. Note the size and shape of the damage as well as the frequency of watering, fertilizer, mowing habits, and sunlight in order to diagnose the disease correctly. Take a sample of the affected grass (blades, roots, and soil) to your local cooperative extension office for analysis.