Here's another photo

I've got some friends that had lawn problems, some insect eating the roots and stems. Above ground it looked similar to what yours looks like. From memory they were the catepillars of a beetle.

It could be any of the things you mentioned . You won't necessarily see anything "eating" the lawn, if it's lawn grubs you may see some waspy things hovering round, but otherwise you need to lay out a bit of wet material - a hessian bag, or a bit of old towling, overnight. Not on the brown area, more towards the border with the green, as they would be moving on in search of roots. If you get up early in the morning and lift the bag you may find the curl grubs still up on the surface feeding, then you know what to do to spray.
Don't cut too short in this hot weather, you'll just burn the blades and expose the roots to sun or heat burn as well.
Also don't chuck fertilizer on it as a "cure-all" as you can just create more problems for re-growing roots.
Ditto water-saver, you really need to do this when it's wet and getting wetter, with rain.
Don;t know what area, the house walls look fresh, is it a new house? If so you might get some settling in probs from cement /foundations etc leaching into the ground, also sometimes town water can be quite heavily "chemical". I should test for lawn grubs first, and just try to keep up the water for a bit, one deep water then lessening, to harden it up gradually, and don't scalp it again

Well I'm at Tweed Heads and to be perfectly honest, your lawn's looking better than mine. I've been over sowing mine here and there with Sir Walter buffalo from Bunnings and I'm acutely aware there has been NO bloody rain this growing season: I've had to water the new stull nearly very day just to get it started. I agree with Allison, don't cut it too short, in fact I might suggest you don't cut it all until the rains come. Also, I wouldn't feed it either until then.

b.

Hey guys thanks so much for the advice. We have had some heavy rains over the last 24 hours which i think is helping with the heat issue/water issue. Ive raised my mower blades by 2 spokes and will wait to see after the rain how its all going. From what i can see i think i may have cut it just a bit to short in the areas mention and the roots have copped a bit of a stinging.

Im going to lay off the fertiliser and just monitor it over the coming weekend and if i find any bug related issues give it a spray with some agent.

Thanks for all the help guys. Funnelweb, hopefully your Sir Walter gets a chance to sparkle after the rainds come. The Sir Walter/Palmetto breed of grass is a great thing for the kids to play on when its lush :)

Thanks again.

Thanks Bagsy, yeah I had a goodly drop last night too - 20 mils - which will help, hopefully in a few days we might get a drop more. The best advice is don't cut it too short, especially in the dry seasons, and only feed it when it's growing well, that is, during good rain seasons. I'd like to give mine a sprinkle of lawn food but I'll hang off until I see some positive change in the weather.

Good luck

b.

There
are two possible issues here – heat stress and poor mowing. Firstly: during hot
days, the grass blades don’t have enough moisture to endure the wear. Try
watering it to encourage growth. Secondly, it might have something to do with your
mowing pattern. Do not mow too low otherwise the soil will be directly exposed
to the sun and thereby weakening the roots. Personally, I have Sir
Walter and
found it to be much more resilient to heat and drought.