western-queensland-gardening-guide.pdf - South West NRM

Stem injections of insecticides to control pests in trees
Insect pests in large trees are often hard to control using normal methods such as
spraying. An alternative technique is to "inject" the tree with insecticides which are
systemic.
These insecticides go through the sap flow to poison any pests which eat parts of the
tree.
The technique is reasonably simple, but provides only short- term control and does
cause some damage to the tree. It should only be done to control heavy infestations
which seriously threaten the health of the tree.
It is also recommended that trees be given water and fertiliser and/or lime, dolomite
or gypsum as required, to promote uptake of chemicals and recovery and continuing
good health of the tree.
Trees which are badly affected and in serious decline may not benefit.
Method of stem injection
Holes should be drilled only as far as the sapwood of the tree and not further into
the heartwood (see Figure 22). Holes are drilled with an 8 (3/8 inch) drill bit
(or similar size) at a downward angle of up to 4 5 O into the trunk of the tree at a
convenient height. Holes are drilled around the tree at a rate of 1 hole per 7.5 cm
diameter of trunk, (that is a tree with a trunk 30 crn wide requires four holes).
The holes should then be filled with Rogor 400 (dimethoate) insecticide using an
eye-dropper or squirt-bottle to achieve 2 mL of chemical in each hole. If the hole
cannot take 2mL allow half an hour for some of the chemical to soak in, then add
the remaining chemical. It is important to inject the insecticide i
holes are drilled to ensure continuous sap flow.
The holes should be left for a several hours to allow for chemical absorption and
then plugged with either wooden dowels or putty. The holes cannot be reused.
tree
Figure 22. Injecting insecticides into a tree