Fertilizer burn is a common cause of brown grass. Applying too much fertilizer to the lawn causes chemicals to build up and dry the grass out, causing it to turn brown and die. Cutting the grass short and watering it frequently helps it recover from fertilizer burn over time.
According to the University of California Davis, billbugs can kill off grass. Billbugs feed on the grass, leaving it straw-colored and dying. Raising mower blades and ensuring that the soil drains rainwater helps control damage caused by billbugs.
The grubs of a number of beetle species feed on grass; large infestations can destroy a lawn. Grubs are small, white and worm-like and can be seen in the soil if present in large enough numbers. Fertilizing, over-seeding the yard and applying pesticides to the grass helps control grubs.