Hi Breeindy.
I've had a similar pest problem growing some 200 plants under a tree in my yard. I was periodically dipping all the plants in pyrethrum but have recently found an easier way - I bought a litre of very strong pyrethrum. It was expensive ($185) but much cheaper than the 200 ml bottles from Bunnings in the long run. The litre mixes at 1ml/litre rather than 10ml/litre for the stuff from Bunnings. So I've got over 100 watering cans of pyrethrum in one shot.
I water in the afternoon and an hour or two later mix up a few watering cans of pyrethrum. I've just done the first hit and intend to follow up in about 3 weeks. That should give any eggs time to hatch but should be before any grubs are old enough to lay more eggs.
I've never had a problem with the plants using pyrethrum but can't guarantee that some species may be sensitive. In my experience pyrethum kills snails, slugs, all kinds of crawly grubs, roaches, ants, earthworms (unfortunately) and spiders which for some reason just love hiding in my pots.
I got the pyrethrum from this mob:
>> Py-Bo << Material Safety Data Sheet
They also have a 250 ml bottle which may suit.
Cheers,
Aus.