Not sure we can be much use really, Tug - the crabgrass we get is Digitaria sanguinalis, and I don't think I've ever seen any in lawns, so its not a big problem like it is North America. There are other varieties which you probably get, but the one we get is an annual, and the advice to deal with it is to dig or pull it out when seen, before it sets seed.

What you say is true, Bamboo. Unfortunately, when a customer has crabgrass seedlings every 6 inches in a 3000 square foot lawn, it is hard to say, "Pick them all out.", like I had to in my father's lawn. We have the same kind of crabgrass, Digitaria sanguinalis, plus some D. ischaemum, but the large crabgrass dominates. I was hoping to get more input from The American members.
Of course, that much crabgrass is a sign of poor maintenance, and will mostly disappear with good maintenance, but that could take a few years.
Ah, well, still hoping for more info.