Pests and Diseases
One of the most important aspects of tree care is the plant’s health. This involves the identification and control of weeds, pests and diseases.
Often if a tree is stressed it is prone to insect attack. Therefore the stress should be alleviated for the plant to build up its own defence system. Stress on a plant could be caused by any of the following:
Lack of water.
Machinery damage (i.e. mower damage at the base of the tree)
Poor pruning techniques (i.e. flush cuts or leaving stubs)
Some types of trees and shrubs, especially fruit trees, have been bred for pest resistance or immunity, which can aid in preventing pest attack.
There are beneficial insects. Often when a broad spectrum pesticide is used, beneficial predatory insects are also killed. For example some lady birds feed on the larvae of aphids and other sap sucking insects. Therefore the insects need to be identified for narrow spectrum or specific insecticides to be used.
Common insects and pests which attack trees
The following is a list of common garden plants and the pests which frequently attack.
Passion vine hopper, pimple gall.
Borers, caterpillar, wasp and beetle galls, scale.
Pine Bark Weevils, borers, scale.
Leaf gall, borers, white fly, galls.
Scale, borers, thrip, saw fly.
Aphids, thrips, scale, caterpillars, borers, weevils, insect galls, termites, leaf hoppers, beetles, possums.
Caterpillars, scale, mealy bug, mites, root nematodes, psyllids, white fly, leaf miners.
Looper caterpillars, white fly, scale, borers, mites.
Scale, thrips, aphids, borers, beetles, weevils, caterpillars.
Scale, thrip, leaf miner, insect galls, borers, root nematodes.
Caterpillars, mites, woolly aphids, leaf hoppers, borers.
Aphids, fruit fly, scale, caterpillars, wasp galls, borers, mealy bugs, thrips, leaf miners, nematodes, mites.
Possums can be very destructive to trees. Firstly they damage the bark on the trunk and branches on their way up the tree. Secondly they feed off the new leaves of the plants, then when the tree cannot put on new growth any longer the possums start to eat the mature leaves. This puts the tree into severe stress as more and more of the tree is defoliated.
Once the tree is stressed the possums usually continue to defoliate the same tree, until it cannot sustain the possum’s appetite any longer.
If possums are not controlled, they can lead to the eventual death of the tree. One of the most effective methods of deterring the possums is to install a possum guard around the trunk of the tree. The guard is now commonly made of heavy duty clear plastic, 1.5 m wide wrapped around the trunk 1.5 to 2 m from the ground, which stops the possums from climbing the tree. This method is only effective if there is no other access for the possum into the tree. For example branches may be touching a roof, the ground or another tree.
The second alternative and a more costly one, is to install electric fencing along the trunk and major branches. This method is usually used when the tree can’t be cleared from other access points. The electric fencing doesn’t seriously harm the possums but acts as a deterrent.
Longhorned or Longicorn Beetle
These beetles can vary in size from 5mm to 60mm, and have a brown or gray pattern on their backs, all having the same basic shape, with very long antennae. These beetles only chew on few new shoots or on young bark, yet the larvae can be fatal to the tree’s health.
These beetles lay their eggs in cracks the bark. When the larvae hatch they tunnel in under the bark. If the tunneling is extensive (often over a few years) the larvae can ring bark the tree by severing the cells that transport all the water and nutrients from the roots to the branches.
The larvae are cream coloured and are usually hard to detect because they are deep within the wood of the tree. If you notice large round holes approx. 1cm in diameter, with sawdust in and around the hole it is most likely your tree has been attacked by the longicorn beetle.
The beetle usually attacks Eucalypts and it is harder to detect on rough-barked species. The attack usually occurs within the first 3m of the trunk and on upper branches.