PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Pest cycle
There is a complete metamorphosis (egg,
larva, pupa and adult) with 1 generation every
1-2 years. Eggs are laid on the surface of the bark,
usually at branch junctions, and the larvae hatching
from the eggs burrow downwards into the tree
creating short tunnels. The tunnel is increased in
size as the larva grows, until it is 6-10 cm in length
by the time the larva is fully grown. When fully
grown the larva closes the entrance to the tunnel
with a wad of silken web and chewed wood and
changes into a pupa. Moths emerge the following
summer.
‘Overwintering’
Probably as caterpillars or pupae in tunnels in
trunks and branches.
Spread
Mainly by moths flying. Infested wood could
spread caterpillars and pupae.
Conditions favouring
Trees stressed by poor soil, inadequate irrigation,
poor drainage. Trunks damaged by sunburn may be
more susceptible.
Management (IPM)
Are you a commercial grower or home gardener?
1.Obtain/prepare a plan if this borer is a
problem, which fits your situation.
2.Crop, region. Recognize variations for your crop,
eg ornamental, commercial, and for your locality.
3.Identification of pest may have to be confirmed
professionally (page xiv) to avoid mistaken diagnosis
as larvae of wood moths or beetles which make longer
tunnels and are more difficult to control.
4.Monitor pest and/or damage and record results as
recommended. Inspect deciduous trees during
dormancy in winter when damage is easily
observed. Frass is easily seen. The giant wood moth
(Xyleutes cinereus) is monitored in some eucalypt
plantations in coastal areas of Qld, and northern NSW.
5.Threshold. How much damage can you accept?
Have any thresholds been established? Do you need to
calculate your own threshold?
6.Action is usually taken when infestation is first
noticed to avoid serious damage to smaller trees.
Prune to remove damaged branches, fertilize and
irrigate to promote vigour. Treat remaining borer
tunnels as recommended. In extreme cases treat major
hosts in your cropping area.
7.Evaluation. Check trees regularly for infestation. If
the frass is visible again then the borer is still active and
further treatments will be needed. Review the control
program and monitoring techniques to decide further
improvements, especially cultural/sanitation practices.
Control methods
As caterpillars do not tunnel far into the wood, this
borer is easy to control on small trees. Other borers
are not usually noticed until they have done much
damage and larvae have penetrated deep into the
wood. Apply control measures when infestation is
first noticed. The most convenient time to do it on
deciduous trees is usually during winter pruning,
when damage is easy to see. If large trees are badly
affected contact a qualified arborist to properly
assess and treat the damage.
Cultural methods.
Fertilize and irrigate trees appropriately.
Provide good cultural care, eg adequate
drainage, irrigation, good fertilizer practices, etc.
Judicious pruning at the correct time may
stimulate vigour and protect limbs from sunburn.
Make all pruning cuts cleanly so that stubs are
not left to dieback and so encourage further borer
attack. Trim ragged edges around the damaged
area.
Sanitation.
If the problem is extensive, or occurs over
more than one season, consider either treating or
removing other major hosts in the areas such as
plums or thickets of black wattle trees within
50m of commercial plantings to reduce buildup
of moth populations.
If small twiggy growth on shrubs or trees
has been attacked, prune off. Consider removing
severely damaged limbs during pruning.
Cut back severely infested branches well
below infested sections and paint the cut surface
with fungicide paint if recommended.
Do not leave prunings lying around as
moths may emerge to lay eggs on other hosts.
Biological control.
The wasp (Trichogramma carverae) lays its eggs in
the eggs of the fruit-tree borer and is being studied
as a possible bio-control agent. There are several
other parasites and predators of the larvae.
Physical methods/Insecticides.
These are mostly suitable if only a few trees are
involved as in a home garden situation.
Remove webbing and sawdust-like material to
expose damaged wood and caterpillars which
can then be squashed or if they are in the tunnel
either poke a thin wire down the short tunnels to
kill the caterpillars, or squirt a household
insecticide into the tunnels.
Only in severe infestations is it necessary to
spray trunks, branches and leaves. Seek advice.
If considered necessary, smooth damaged wood,
plug tunnels with putty or similar material.
Light trapping of moths at night is being
researched.
Table 11. Fruit-tree moth borer – Some insecticides.
What to use?
INSECTICIDES, eg
When and how to apply?
Seek advice regarding spray applications.
Insects and allied pests - Lepidoptera (butterflies, moths) 97