Grubs can be a huge problem in some lawns. I feel your pain.
In North America, we have a big problem with Japanese Beetles. These pesky creatures can destroy lawns and leave large patches of brown, seemingly dead grass.
The best way to treat actual lawn grubs is to kill them with an application of a grub killer like "Bayer Grub Control". One application of this is usually enough to kill the grubs without having to worry about putting a lot of insecticides on your lawn. If you can catch the Beetles BEFORE they lay and put grubs in your lawn, you can use Beetle Traps. These work great for Japanese Beetles, and some other varieties;
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I'm no expert on Australian Beetle Varieties, but I imagine that your grub control is not much different from North America.
-Good Luck!
I know this post is about grubs in Australia, but I can't help but bring to light a few facts about Japanese beetle traps.
1. They will collect beetles, but they also draw beetles to your property.
2. They will not collect all of the beetles that come onto your property alone, so other measures still need to be taken to help prevent them from destroying flowering plants. This can be accomplished by either using an insecticide, or spraying the beetles with dish soap and water. (Believe it or not soap and water will kill them)
3. many people make the common mistake of putting the traps near their flowering plants thinking the traps will draw all of the beetles away from the flowers. This is absolutely the wrong thing to do. If anyone is considering using the traps only put them on the perimeter of your property. This will help draw beetles inside your property away from plants, and beetles outside of your property to the traps instead of to the plants. As I mentioned earlier, this won't prevent all of them from getting to the plants, so be prepared to use other measures as well.
4. When disposing of the beetles that have been trapped first dump them in a bucket of soap and water and make sure they are all dead. (Japanese beetles bore into the ground to reproduce. If they aren't dead before they are dumped out the infestation will worsen.) finally, once you are sure they are dead you can dispose of them anywhere. Some claim the odor of decaying beetles will prevent live beetles from entering the area, but I don't like the smell either, so I dump the dead beetles in the ditch on the farthest edge of my property.
I know this post is slightly off topic, but if the beetles in Australia are similar to what we have to tend with here in the states the methods mentioned above will help. I had a huge infestation of Japanese beetles this year. Their favorite foods seem to be rose of Sharon, crepe myrtles, and roses. I have all of those on my property. And caught enough beetles to fill a 25 gallon drum.