Before you call 911 on a lawn-threatening pest situation, keep in mind that brown grass is often a result of poor maintenance, site conditions, or summer dormancy rather than an infestation. Be sure your lawn isn't being mowed too short and that it is not suffering from soil compaction, drought, or nutrient deficiencies.
What Causes It
White grubs chew on grass roots, causing irregular, brown, dead patches in the lawn.
Fast fix: Apply parasitic nematodes (genus Heterorhabditis) to the affected area; then water well.
Prevention: Apply milky disease spores, which parasitize Japanese beetle grubs and survive for several years.
Sod webworms cause dead spots by severing grass blades and pulling them into the ground to eat. They prefer new lawns.
Fast fix: Apply BTK about two weeks after moths appear, when pests are in their larval stage.
Prevention: If the problem persists, overseed with endophyte-enhanced grass varieties.
Shabby, Worn-Out Looking Lawn
If your lawn looks weak but you can't identify the cause, get out a ruler and check the depth of thatch. Less than a half inch of thatch acts like mulch. A deeper layer keeps water and nutrients from reaching the grass roots.
What Causes It
Thatch, a springy mat of grass roots and stems on the soil surface, is the result of excess fertilizer use. It is not caused by letting clippings fall onto the lawn.
Fast fix: Scrape out the thatch with a hard-tined rake (special thatch rakes are helpful but not essential).
Prevention: Spread a layer of compost on top of the soil to encourage earthworms to thrive in the soil and break down the thatch layer at the same rate at which it is being formed. Use slow-release organic fertilizers only.