Now is the time to have a look at your callistemons (bottlebrush) for sawfly infestation.
While not a serious threat to larger more established trees these larvae can totally defoliate seedlings over a few days. The recommended way to deal with them is to hand (wearing sturdy gloves of course) pick them off. They can also be sprayed off with a hose but in these times of drought that would be unthinkable. The two photos below show two callistemons (one without infestation and one with) that were planted at the same time showing how sawflies can damage young shrubs.