Grubs live beneath the grass, where they eat the grass roots. If you suspect their presence in your lawn, remove a block of sod and count the grubs. If you have as many as five per 1/10 sq. meter, treat your lawn with nematodes.
The sod webworm is a lively brown worm about 2 cm long that feeds on the leaves and stems just above the grass crown. Healthy well-maintained turf will often tolerate and recover, but weak grass may be killed by sun-exposure of the crowns. Thus, the grass will turn brown.
Chinch Bugs are small black insects about 1/2 cm in length that are usually found on drought-stressed lawns where they puncture grass with their needle like beaks and suck the fluids out. The damage shows large irregular yellowish brown patches, usually along the edge of a sidewalk, curb or foundation.