Work out which one it is
The fix depends entirely on the cause, and watering a grub problem or spraying a dry patch just wastes time. Run through these and see which one matches.
1. Lawn grubs or army worm
Large areas browning off fast in mid to late summer, when the lawn is otherwise getting water. The edges of the patch look chewed and ragged, and the patch spreads day by day. Birds working hard over that part of the lawn is a strong hint, and you can often see bright green grub droppings down in the thatch.
This is the most common cause of a healthy Central Coast lawn suddenly going backwards in January and February.
2. Heat and dry
Same spots every summer, and usually the obvious ones — beside a concrete path, along a north-facing brick wall, on a slope, or over a shallow layer of soil above rubble. The grass is crisp and crunchy rather than slimy, and it browns off gradually rather than overnight.
A screwdriver pushed into the patch will hit hard, dry soil. Fix is a deep soak rather than a daily sprinkle, and a higher cut over summer.
3. Fungal disease
Roughly circular patches, often with a darker or yellowish ring around the edge, appearing after a run of warm, humid, still nights. Brown patch and dollar spot both turn up on the Coast in that weather.
Watering in the evening, over-feeding with nitrogen, and mowing wet all make it worse. Cut back the evening watering first, then treat with a lawn fungicide if it keeps spreading.
4. Dog urine
Small, sharply defined circles, often with a ring of extra-green, extra-lush grass around them. That ring is the giveaway — the nitrogen is fertilising the edge and burning the centre.
Hosing the spot straight after helps. So does giving the dog one part of the yard to use.
5. Compaction and wear
Bare or thin tracks in the exact places people and pets walk — gate to back door, around the clothesline, under the trampoline. The soil there is hard enough that water runs off rather than soaking in.
Coring or aerating fixes it properly. A stepping-stone path fixes it permanently.
6. Scalping
Yellow patches that appeared immediately after a mow, on the high points and along ridges. The mower has taken the crown of the grass off where the ground rises. Raise the cut height, and level the bumps with a topdress if it keeps happening in the same spots.
When it needs turf rather than treatment
Warm-season grasses spread by runners, so most patches will fill back in on their own once the cause is dealt with, given warmth and water. If a bare area is bigger than about a square metre, or the roots have gone entirely, fresh turf is faster than waiting.