My lilly pilly hedge is 9 years old and we live in Victoria. Last year it had problems with bug infestation and I sprayed it and fertilized it and it bounced back extremely well with new growth and looked really healthy. Now some 6 months later it has thinned out badly. There are no signs of any bugs. Any thoughts how to encourage new growth and to thicken foliage? Should I apply fertiliser more heavily? I've used an all purpose Powerfeed in the past purchased from Bunnings.