Growing a hedge can be difficult because of pests.
Most hedges are planted with one variety. It is best to choose a single variety of hedge plants.
Lilly Pilly psyllid (attacks Syzigium Lilly pillies, leaves are damaged in spring and winter, there are insecticides for these), Hibiscus Beetle, which attacks hibiscus and other plants, and Aphids, which attack most soft foliage.
Caterpillars
There are many types of caterpillars around the globe, but they are easy to control as they hide on the ground or on the inner stems. Pyretherum is a knock-down insecticide that can be used to control them. You can also use a systemic insecticide available at your local nursery (follow the instructions).
Ground-borne, root-eating grubs
There are many kinds of ground-based beetle larvae. Once you dig deeper, it is difficult to see them. These grubs are known by many names, including “cock chafers” or “curl grubs”. They consume the roots and quickly kill the plants. This is unlike other pests that will decimate hedge plants. You can control them with chemicals that are available at your local nursery. Systemic insecticides can be very useful for controlling pests on hedges. The plants absorb the insecticides and if they are eaten, the poison is absorbed by the plants.
For advice about your specific pest problems, consult your local Nurseryman/Garden Centre.