PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Diagnostics. Look at twigs for encrusted scales.
Although the scale is visible throughout the year, it
is most readily detected in winter on deciduous hosts
when trees are bare of foliage and on fruits during
harvest.
Low populations of scale are hard to detect
and can become major infestations before
they are noticed.
Honeydew is not produced.
Dying branches in autumn.
Limbs and trunk covered with ‘dust’ (scales).
Hand lens is needed to confirm identification.
May be necessary to consult a diagnostic service.
Determine whether scales are dead or alive. Lift
the hard grey scale cover with a pin or finger nail
and examine the insect body underneath. Dead
scale insects will be dry and shrivelled while live
scales will be soft and fluid-filled.
Pest cycle
There is a gradual metamorphosis (egg,
nymphs and adult) with several generations each
year. In spring, the 2 nd stage nymphs (‘black
caps’) begin to grow and are usually fully grown
by the time the trees come into bloom. The
females when mature produce active 6-legged
young (crawlers) which make their way from
under the parent scale, move about for a while,
then settle down near the adult to feed by inserting
their long tube-like mouth into the sap; they lose
their legs and begin secreting their protective scale
covering. They remain fixed in this one place for
life. Male nymphs develop a pair of wings and
emerge. The period from birth until young are
again produced is about 6 weeks, as 1 female can
produce as many as 400 live young, the increase in
numbers of scale insects in one season is obviously
tremendous! Large populations can build up in one
season, covering all the bark on the tree.
‘Overwintering’
nd
In colder districts, as 2 stage nymphs, often
called ‘black caps’. In warmer areas, all stages
may be found.
Spread
Movement of infested nursery stock is the main
method of spread.
Nymphs may be blown by wind.
Nymphs may also be accidentally carried by
birds, insects and humans, and on boxes, bags,
fruit and other materials.
Conditions favoring
Relatively warm, dry climates but will tolerate
humid or cold conditions.
Management (IPM)
Are you a commercial grower or home gardener?
1.Obtain/prepare a plan that fits your situation.
Follow any control measures prescribed by legislation.
San Jose scale often develops to damaging proportions
before growers become aware of its presence.
2.Crop, region. Recognize variations.
3.Identification. If in doubt consult a diagnostic
service (page xiv). Scales are obvious on fruit and
leaves. Scales on limbs are easily seen with a hand
lens during winter.
4.Monitor scales and damage, tag infested trees.
Know when crawlers should be around.
Use a hand lens to see crawlers. Check for holes in
armoured scales which indicate parasites active;
check during monitoring if the scales are still alive.
Examine bark of trees during winter pruning,
dormancy, fruiting and after harvest, for cracked,
rough, scaly bark, dead twigs. Check prunings to
make sure that scale has not developed in tree tops.
Suspect trees should be checked thoroughly for
live scales. Check trees downwind of infested trees.
Monitor trees for crawlers using double-sided
sticky tape in spring if inadequate control is
achieved with dormant sprays.
Traps are available to monitor male scale flights in
spring. Desire sticky and InSense Lure traps
available for San Jose, red scale and citrus red scale:
http://insense.com.au/products.htm
Monitor scale populations on fruit during
harvest and grading. Tag infested trees and
record which blocks are infested.
Keep records of all infested trees (page 39).
5.Threshold may be nil tolerance for export grade
fruit and if any scales are found control is prescribed
by law. How much damage can you accept?
6.Action/control for some markets is compulsory by
law. Trees can be thoroughly sprayed with an
appropriate registered chemical. The aim should be to
eradicate San Jose scale from every tree in the orchard.
In practice this is rarely achieved. All infestations
should be controlled immediately. Winter oil is the
preferred treatment on deciduous hosts. Due to potential
damage from the pest on apples annual dormant sprays
are recommended in some areas. Occasionally
inadequate control is achieved with dormant sprays.
7.Evaluation. Review IPM program to see how well
it worked. Recommend improvements if required.
Approximately 6-12 weeks after the initial oil spray
during dormancy on deciduous hosts, examine scales
by removing scale covers and confirming that they are
dead. If any live scales are found consider a spray with
other insecticides. Repeat this procedure until no live
scales are found. Record results.
Control methods
This scale is difficult to control. It is a ‘proclaimed
pest’ in some areas and its control is required by
law. Scale should be eradicated from every tree in
an orchard.
Sanitation.
Remove dead or dying infested branches.
Reduce movement of staff through infested areas;
crawlers may be carried on clothes and equipment.
Insects and allied pests - Hemiptera (bugs, aphids, etc) 169