How healthy are your trees is your tree showing signs of stress, have they been attacked by a pest/insect. Some tree Pests such as below can damaged and kill your trees if not treated.
Thaumastocoris peregrinus, Winter Bronzing Bug is a pest of Eucalytpus trees, especially narrow leafed Eucalytpus trees. It is a cytosol feeder of tree leaves, which means it feeds on the inside material of the leaf cells and the cell dies. The leaves cannot do their job of photosynthesis.
The symptoms of insect attack are that the tree leaves turn a silver, spotted yellow to bronze colour. This insect pest can be part of the cause of decline in the tree health of Eucalypts in the Sydney basin.
The infested trees will turn the reddish brown to bronze during winter. If the infestation is severe the trees will start to drop their leaves. Twig and branch dieback may also occur. If this continues it will lead to tree decline and possibly the death of the tree.
Chemical control
In Australia the chemical control option for T. peregrinus is tree injection.