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Brown Spots in Lawns

Posted 7/6/2007

Irrigation problems are the number one reason for brown lawn spots. The irrigation system must be designed, installed and maintained properly. Irrigation sprinkler heads must have head-to-head coverage (water from sprinkler heads should overlap enough to reach neighboring heads in the vicinity). This is a necessity. Sprinkler heads should have nozzles that are all the same type, not a mixture of several types on the same system. Each sprinkler head should have the same nozzle so that they put the same amount of water down on the lawn during an irrigation cycle. Mix and match heads may not do this. Mix and match heads in a lawn will waste water and affect your water bill.

Reducing water use to dry up swampy parts of the lawn will result in brown areas in other parts. Grass responds to a lack of water by first turning gray-green or smoky colored. If a lack of water persists, the area turns brown. If not watered, eventually the entire grass blade and the plant will turn brown. This results in brown spots that get larger as long as the water is not available. A few days after rewatering, the grass blade tips remain brown while the base of the leaf blade is green. Brown spots resulting from a lack of water, and then rewatered to bring it back to life, are easy to detect. Grass blades near the brown areas will have a brown dieback on the tips. If the grass blades surrounding the brown area do not have this brown dieback, the problem is probably not related to a lack of water.

Usually brown spots resulting from a lack of watering will have a distinct location in the lawn. They will be located generally in the same spots in a lawn in relation to the sprinkler heads. Another reason for brown spots due to watering, not mentioned very often, is from excess pressure in the irrigation lines leading to the sprinklers. Some areas of the valley have a lot more water pressure than other areas. Lawn watering systems are designed to operate within certain pressure limits. If this pressure is excessive, water from the sprinkler heads comes out under extreme pressure. This results in a spray of water known as "fogging". You can see it easily if you watch the water coming from the sprinklers. This fogging results in a mist that will move with the most gentle of winds. Since irrigation systems are designed to work best under a very narrow range of pressures, water is applied unevenly to the lawn when pressure is excessive. The best way to handle this is to install, or have installed, a pressure regulator on the irrigation system. This will keep excessive pressures under control but not affect the system if water pressure is insufficient.

If you have a dog or if it is your front lawn that has spots and you suspect a dog problem, remember that spots from urine are relatively small, somewhere around 4 to ten inches across with a dark green ring of taller grass encircling the dead spot.

The next problem that could cause brown spots is damage from insects. Cutworms can be a problem. They will come up from the ground at night and cut off grass blades at the ground level, causing depressions in the grass and eventual browning. White grubs could be a problem later in the summer. In the early morning, grab healthy looking grass close to the damage and see if some of it pulls easily from the soil and has no roots. If you can remove some grass like this without roots this could be the problem. If this is the case, you really need to find the insect and have it identified. We can help you do that. If we do not know what it is, we take a picture with a microscope camera and e-mail it to the state entomologist.

Summer patch disease of tall fescue is a hot-weather disease that normally begins to develop during the hottest time of the year. Most diseases on tall fescue are more likely to develop in July, when the summer afternoon overcast skies usually start moving in.

White grub damage, even though it can start at the ten-inch size initially, can get much larger. Since the white grubs eat the roots. the newly dead grass pulls up easily. Dig down in the area on the border of the dead grass and see if you can find the shrimp-shaped grubs. They can range in size, depending on how old they are, but can be as large as an inch across.

The symptoms of summer patch in the very beginning are a frog-eye appearance of dead grass, with green grass in the center, perhaps one to two feet in diameter. This results from dead grass dying in curved or circular patterns and then newly infected grass dying to the outside of the curve. Several of these patches may begin showing up at the same time. These frog-eye dead spots begin to merge into a mottling of dead grass interspersed with tufts of green grass. In advanced stages, most of the lawn may die, leaving behind just a few tufts of green grass up to six inches in diameter. This is a fungus disease and usually occurs mid summer, most frequently on fescues, rye and bluegrass in our area. This disease can be transported on equipment, the bottom of shoes and through draining water. The fungicides recommended for this disease are Bayleton, Banner, Chipco 26019 and a few others. For a complete list and full description of this disease call Nevada Cooperative Extension at (702) 397-2604. These fungus diseases do not go away very easily without treatment.

The University of Nevada Cooperative Extension is an outreach arm of the University that extends unbiased, research-based knowledge from the University of Nevada and other land-grant universities to local communities. Educational programs are developed based on local needs, often in partnership with other agencies and volunteers. For more information about the University of Nevada Cooperative Extension, please visit the website at www.unce.unr.edu or call (702) 397-2604 or (702) 346-7215.

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