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 each year.
Adults emerge from trees in spring and summer,
mating occurs shortly afterwards. Egg laying
begins and continues throughout most of summer.
Females lay their eggs singly into rough bark,
cracks of twigs and small branches or in wounds.
They gnaw a circular patch about 1 mm in
diameter around each egg. After hatching larvae
eat their way into the wood and tunnel either
upwards into the trunk or downwards into the roots
for distances up to 1 metre. The circular patch of
bark dries and falls out leaving a round pit which
exposes the sapwood. When fully grown, larvae
pupate just under the bark at the end of their
tunnel. Adult beetles start to emerge from trees
during spring through oval exit holes in late
spring or summer.
‘Overwintering’
In trunks, limbs, roots of host plants as larvae.
Spread
By adults flying. Movement of infested wood.
Conditions favoring
Adult female longicorns prefer to lay their eggs
on trees that have been weakened in some way,
eg drought, waterlogging, sunburn, often
following canopy pruning) or severe pruning,
lawnmower or storm damage, old age, insect
damage, disease, or fire damage.
Research suggests that excessive use of
fungicides kill fungi which attack larvae and
may result in increased borer damage.
Management (IPM)
Are you a commercial grower or home gardener?
1. Prepare a plan that fits your situation.
2. Crop, region. Recognize variations depending on
the crop, eg citrus, wisteria.
3. Identification of borer must be confirmed. Consult
a diagnostic service if required (page xiv).
4. Monitor pest and/or damage and record results as
recommended (page 39). Seek advice but you could
monitor all blocks that have a history of borer
problems, a rating system for citrus, eg.
0. No damage
1. Small patch on the trunk or a limb
2. Trunk and a limb with 2-3 patches
3. Most lower limbs and trunk with serious patches
4. Extensive damage, serious dieback, secondary rot.
5. Threshold. For citrus, when the average rating is
2 or more. How much damage can you accept?
6. Action. Take appropriate action when any threshold
is reached.
7.Evaluation. Treated trees should be inspected at
2-3 weeks intervals for the next few months after
treatment and any missed tunnels or new larval
damage treated. Review IPM program to see how well
it worked. Recommend improvements if required.
Control methods
Control is difficult as damage is not usually noticed
until larvae have penetrated deep into the wood.
Cultural methods. Maintain tree vigour,
adequate drainage and irrigation, fertilizer practice.
The best treatment for all tree problems is to
ensure that the trees are as healthy as possible and
therefore have the resources to establish their own
internal protective walls. Judicious pruning at the
correct time may stimulate vigour. All large
pruning cuts should be made cleanly so that stubs
are not left to die back and encourage further borer
attack. Surfaces may be painted as soon as
possible with an insecticide. Seek advice.
Sanitation. Control of larvae already in the
wood is difficult. Regular pruning and burning of
infested small branches may prevent loss of large
sections of trees and minimize build-up of
longicorns within the planting. If the main trunk is
damaged affected tissues may be scraped away.
Biological control.
Natural controls. Predatory beetles feed on
larvae. Parasitic wasps attack larvae, papery
cocoons and pupae are often seen in tunnels.
No biological control agents seem to be
available for purchase or been released as yet.
Physical and mechanical methods.
In small plantings, short tunnels may be probed
with wire to kill larvae. Dissecting larvae from
channels is discouraged due to mechanical damage
caused by knives.
Insecticides.
Small accessible infestations involving
only 1-2 small trees. Clean away loose bark until
the perimeter around the wound is healthy bark,
destroy any larvae found, then paint on or squirt
in a household insecticide which will be
absorbed without damaging the tree.
Well established trunk boring insects cannot be
controlled by spraying, tree injection or by just
placing insecticide in oval exit holes on the bark.
Large infestations may be treated by a licensed
operator. Place nozzle over one of the tunnel holes
and squirt insecticide under pressure into the
tunnel. Penetration along the length will be
obvious when the chemical seeps from the other
holes along tunnels. Follow-up treatments may be
necessary for several months. A fungicide may be
included if secondary fungi are a problem (?)
Seek advice for individual situations, eg
citrus longicorn damage to citrus.
Table15. Fig longicorn – Some insecticides.
What to use?
INSECTICIDES for Fig longicorn
Group 1B, eg Gusathion (azinphos-methyl); Supracide
(methidathion) DANGEROUS POISON
Group 2B, eg Regent , Legion , various (fipronil)
Group 3A, eg Talstar , Venom , various (bifenthrin)
When and how to use?
Insecticide should only be applied to large trees
and extensive infestations by licensed operators.
Note: Stem injection of insecticides to control foliagefeeding
insects does not control borers which mostly feed in
dead tissue where there is no active conducting tissue.
112 Insects and allied pests - Coleoptera (beetles, weevils)