There are brown spots in my lawn!
Drought--
...not watering deeply enough; sprinkler heads not covering properly. Brown areas are more general than spotty, and probing with a trowel reveals dry soil beneath the top inch or so. Browning is worse on the top or slope of a mound, because water runs off, and in the corners because sprinkler coverage is usually worse there. See our article Summer Watering 101.
Pets--
...female dogs cause burnt spots, which then green up along the margins. Lawns with grasses which spread by runners (bluegrass, red fescue, bermudagrass) will fill back in and get deeper green as the urine becomes fertilizer. Dwarf and tall fescue lawns--which are our most common lawns now-- will develop dead spots which will need to be reseeded.
Heat burn--
...items left on the lawn on a hot sunny day will burn the grass underneath. The base of the leaf and the stem remain green. This can be a kids' wading pool, a tarp, or even a Frisbee.
Insects--
Sod webworm
...feeds on the leaf blade, causing the grass to thin. Caterpillars are 1/4 - 1/2" long and brown, and you usually don't see them. The blades have small chew marks. Small tan or buff moths may be hovering over the grass in the early evening. Insecticides or beneficial nematodes may be used.
Cutworms and armyworms
...feed on the entire blade and crown of the grass, causing the lawn to disappear. Blades that remain have been chewed. Both are tan, grey, or brown caterpillars up to about 1" long. Cutworms curl up when you touch them; armyworms crawl away. Jays and mockingbirds may be feeding on them. Large, fat-bodied moths (not sphinx moths--smaller) fly into the house or around porch lights at night (hence the name Noctuids). Caterpillar-killing products containing Bacillus thuringiensis (BT--an organic pest control), or beneficial nematodes may be used.
Grubs
...feed on the roots, causing the lawn to look as though it needs water. The pattern of browning does not correspond to sprinkler patterns, slopes, or mounds. Tug on the grass and it may pull up like sod. You may find maggot-like grubs just under the surface. The adults are beetles like the June beetle. Insecticides or beneficial nematodes are used to control grubs.
Fungus--
Fusarium blight
...causes distinct dead spots, sometimes in a ring pattern, on bluegrass lawns. It can cause a mottled die-out on mixed fescue/bluegrass lawns as it attacks the bluegrass and not the fescue. Fusarium attacks at the base of the plant and the whole plant is dead. This is why we don't recommend Kentucky bluegrass here. Fungicides containing bayleton can stop the disease from spreading, but infected areas will not green up.
Anthracnose blight
...causes thinning and general die-out, especially in shady, damp areas with compacted soil. It attacks the leaf-blade, killing individual blade, then the stem. It is sometimes called "melting out" because the lawn just seems to "melt" away. Note: if anthracnose is an ongoing problem it is probably too shady for a lawn. Aerating can be helpful. Creeping red fescue may do well if it is mowed high (2 1/2" +), or consider a ground cover.
© 2008 Don Shor, Redwood Barn Nursery, Inc., 1607 Fifth Street, Davis, Ca 95616
www.redwoodbarn.com
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