PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Lacewings (Order Neuroptera), various species
feed on black scales.
Scale-eating caterpillar (Catablemma dubia)
use remnant scale coverings to ‘ornament’ their
grey parchment-like cocoons.
Wasps. Larvae of some parasitic wasps prey on
eggs of black and other soft scales. Adult wasps
also kill scales by sucking their juice.
– Fungal diseases. Several species, eg Nectria
spp., a red-headed fungus (Fusarium coccophilum)
and a felt fungus (Septobasidium sp.) may attack
scales in warm moist autumns and cover scaleinfested
branches with a white fungal growth.
Commercially available.
Some predators may be purchased, eg
mealybug ladybird.
Parasitic wasps (Metaphycus spp.) for the
control of black scale and soft brown scale on
citrus, olives and ornamentals are being
researched.
List of suppliers www.goodbugs.org.au/
Resistant varieties.
Black scale has a wide host range but not all
varieties of a particular species are susceptible, eg
although all citrus varieties are susceptible to red
scale, lemons are preferred.
Plant quarantine.
Avoid introducing infested stock, buds, grafts,
or cuttings into the property or into the
greenhouse. Inspect new arrivals.
Lucid Keys www.lucidcentral.com/ and search
for: Scale Insects: Identification Tools for
Species of Quarantine Significance
Pest-tested planting material.
Only plant scale-free nursery stock.
Physical & mechanical methods.
Ants attracted to honeydew produced by soft scales
can be controlled by applying thick sticky bands,
insecticide sprays or baits around the base of
trunks, to trap or kill the ants. Skirt pruning and
good weed control prevents ants accessing trees.
Insecticides.
Avoid indiscriminate use of persistent broad
spectrum insecticides which kill natural enemies.
Timing. Spray when crawlers can be seen on
leaves and twigs and no liquid exudes when old
scales are squashed. Later stages have a
protective waxy layer which makes them
resistant to insecticides and spray oils.
Spray oils control scales by suffocating the
insect. Plants must be thoroughly sprayed. Oil
will not kill eggs that are under the adult scales.
– Evergreen trees, eg citrus, may be sprayed with
petroleum oil in summer.
– Deciduous trees (< 3 m high) may be sprayed
with petroleum oil when trees are bare in winter.
– Oil sprays also loosen sooty mould.
– Caution when using oils.
If oil is absorbed into the plant, injury will result.
Oils vary in their ability to cause plant injury, the
lower the viscosity of the oil the less likely it is
to injure plants.
Do not spray on days when shade temp is likely
to exceed 35 o C and/or soil is dry.
Ensure that the oil-water mixture in the spray is
well agitated to prevent separation.
Oils are available in varying degrees of
refinement.
If applied at the right time and with good
coverage oil sprays will kill scale without
injuring beneficial insects or the host.
Contact chemicals are only effective against
crawlers. Adult scales with their waxy coverings
are difficult to kill with contact pesticides.
Contact sprays are devastating to all beneficials.
Systemic chemicals should give good control
of adult scales that are actively feeding. Once the
scale has stopped feeding it is too late to control it.
Systemics are absorbed by the plants so beneficials
are less exposed to them.
Ants repel parasites and predators of black scale
and spread scale around the property. Increased
ant activity serves as a good guide to presence of
crawlers of black and other soft scales.
Table 31. Soft scales – Some insecticides.
What to use?
DECIDUOUS SHRUBS AND TREES, eg ash
Spray oils, eg Pest Oil (petroleum oil),
Bioclear , EcoPest Oil, SK-Enspray99 (paraffinic oil)
EVERGREEN PLANTS, eg oleander, citrus
Foliage sprays
Group 1B, eg various products
Group 3A, eg pyrethrin
Group 4A, eg Confidor (imidacloprid)
Group 7C, eg Admiral IGR (pyriproxyfen)
Sprays oils, eg D-C-Tron Plus, Pest oil , Summer oil, White oil
(petroleum oil); Bioclear l , BioPest l , EcoPest l
Oil, various (paraffinic oil); Eco-Oil (botanical oil)
Soap sprays were the original control for scales on the citrus tree
growing at the back door of old homesteads
Soil-applied insecticides
Group 4A, eg Iniator (imidacloprid/fertilizer) – protects young
eucalypts from insect pests including gumtree scale.
Confidor Guard soil insecticide (imidacloprid) is
registered for pink wax scale on citrus
STEM INJECTION – LARGE TREES
Various systemic chemicals are available to kill scale and other sap
sucking insects, but they are difficult to control.
When & how to apply?
Dormant oil applications are the preferred spray
for scales on deciduous plants. One spray is
usually enough. They have few or no harmful
effects on parasites and predators but require
substantial amount of oil for control and there are
no crawlers at that time. Oil sprays smother the
scales, but do not kill the eggs under the adult
scale. Apply after pruning where appropriate.
Do not neglect small infestations. Apply sprays
at the crawler stage, later stages are resistant
to insecticides.
Two sprays during each crawler stage are
necessary because pesticides do not kill the
eggs, the 2 nd spray, therefore, kills crawlers
developing from the eggs still unhatched at the
time of the 1 st spray. A 2 nd crawler stage may
be present sometime in autumn.
The main crawler stage is usually about mid-
December to mid-January but timing will
depend on observation of the stages present and
increased ant activity.
Ensure appropriate spray volumes are applied
to thoroughly drench trees.
Apply after badly infested areas have been
pruned out, some scales can be washed off.
Seek professional advice. Permits may be
required for stem injection use.
166 Insects and allied pests - Hemiptera (bugs, aphids, etc)