Kermit said it best: “It’s not easy being green,” and the color of your lawn is no exception. The goal is to achieve a lush, green and vigorous carpet free from weeds and noticeable imperfections. This can be a feat and with nutrient applications, irrigation and improper mowing, your lawn can end up being inundated with ugly brown spots.
They’re small. They’re the size of a lake. Maybe one is in the shape of a butterfly, or it popped up out of nowhere. How did they get there in the first place?
These dead grass or bare dirt spots could be caused by a number of things, but when in doubt, it’s best to have a professional make a diagnosis. Many clients assume brown spots are related to a pest or disease and needlessly apply pesticides, but some of the most common causes require very different solutions.
Dog Urine
Surprisingly, this is the most common cause of brown spots on residential lawns (Figure 1). Dog urine can manifest as brown or green spots, and on turf with a low nutrient status, act as a localized application of nitrogen to promote grass growth. If your lawn is fertilized though, this addition of nitrogen can cause the equivalent of a ‘fertilizer burn,’ killing the grass. To restore the dead grass, water the area and encourage the dog to use other areas of the lawn. The addition of fertilizer could only make the problem worse, and reseeding in these areas may fail until the excess nutrients have been flushed away.
Environmental Causes
Mainly concerning your soil type, temperatures and irrigation, brown spots are often caused by rocks at or near the soil surface, which don’t allow grass to grow. In the picture below (Figure 2), this lawn was recently seeded on commercial backfill dirt. Remedying this situation may take any combination of raking, core aeration, topdressing and overseeding.
Irrigation is a great way to keep your lawn looking green and healthy. Too much of a good thing can result in—you guessed it— brown spots. Here is a lawn where the irrigation was puddling and killing grass (Figure 3), but an irrigation specialist would be able to correct this issue.
The brown spots in Figure 4 were caused from tarps being left on the ground for too long. While these brown spots are large and obvious, the same thing can happen with smaller items such as toys, tools or even trash in the grass. Grass is especially susceptible to this type of injury during the hot/dry months. When possible, place items on stone or bare mulch areas. Watering may be enough to recover some areas of damage, but if not, overseeding could be a viable option.
Honorable mention: be aware of any liquid spills in the grass like acidic coffee, gasoline or detergents dumped in the grass as a way of disposal. Occasionally, accidental herbicide spills may be to blame (Figure 5).
Insect damage
Grubs are notorious for causing damage to turf. Not only do they cause brown spots themselves, but they can also attract digging by critters such as voles and birds who like to turn a nice lawn into a muddy mess. Insect damage usually requires an application of pesticides, the type of pesticides depending on the time of year and type of bug causing the problem. Consult a professional, preferably one with a valid pesticide applicator card, before applying pesticides to your lawn.
Turf Diseases
We talk about turf diseases as the cause of brown spots last because they are not as common and can be difficult and expensive to control once symptoms appear. One way to positively identify a brown spot being caused by a fungus is to catch it when it’s ‘fruiting.’ When this happens, you will see the fuzz like ‘mycelium,’ which may be white to red in color (Figure 6). You may also notice the grass mat down and turn dark brown or black—not unlike lettuce gone bad.
Some turf disease, like brown patch (Figure 7), can be more difficult to identify. If you suspect the brown spots in your yard are caused by a disease, it is best to have a professional make a diagnosis. Often, samples must be taken to a lab to be identified. Applications of a fungicide should be made only when the disease has been positively identified.
***Photo credits: Tina Graver