PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Conditions favoring
Heavy infestations do not usually occur until
autumn, when summer leaf growth has replaced
foliage defoliated by the previous infestation.
Outbreaks do not occur every year. Not known
why some species have population explosions.
High populations collapse eventually either due
to changes in weather or depletion of suitable
foliage due to feeding damage and premature
leaf fall. Once populations start to decline effect
of natural enemies increases.
Stress due to wind, frost, root damage,
compacted soil, drought, waterlogging may
make foliage more attractive to psyllids.
Outbreaks may occur after a succession of
unusually dry and/or wet conditions.
Prolonged high temperatures are unfavourable.
Management (IPM)
Are you a commercial grower or home gardener?
1.Plan in advance that fits your situation.
2.Crop, region. Recognize variations, eg urban tree
plantings, plantation forests.
3.Identification of pest must be confirmed. Consult
a diagnostic service if necessary (page xiv).
4.Monitor pest and/or damage early, especially new
foliage, to prevent stress and/or death of susceptible
young trees, record results. Check bird populations
which prey on lerps to avoid unnecessary treatments.
5.Threshold. How much damage can you accept?
Have any thresholds been established? If so, what are
they, eg economic, aesthetic, environmental?
6.Action. Take appropriate action when a threshold is
reached, eg improve tree vigour.
7.Evaluation. Review the program and assess its
success, recommend improvements if required, eg
replacing susceptible varieties in young plantings.
Continue to monitor trees after treatment.
Control methods
Control is difficult. Practically there is not much
you can do about large populations on tall trees.
Small trees continually attacked may be better
replaced with less susceptible species.
Cultural methods. Improve general vigour of
trees. It is thought that the more nutritious the sap
(quality and quantity of nitrogen compounds in the
sap), the faster psyllid populations grow.
Biological control. No biological control
agents are available for purchase or have been
released in Australia. Natural controls exert some
control if lerp densities are low. Ants attracted to
honeydew deter insect predators/parasites.
Predators feed on lerp insects but do not exert
sufficient influence to keep attacks in check.
– Larvae of syrphid flies and ladybirds, also
lacewings and spiders.
Table 29. Lerp insects – Some insecticides.
– Birds. Canopy-feeding birds such as pardalotes feed
on the nymphs whereas bell miners feed on the lerp
itself. Flying adults are captured by swallows and
martens. Aggressive colony-forming bell miners,
the honeyeater (Manorinus melanophrys), in the
canopy of unhealthy Sydney blue gum (Eucalyptus
saligna) has been well reported. Bell miners are
thought to reduce the effectiveness of natural enemies
by feeding directly on or interfering with their
reproduction thus causing more damage. But it may
be that when lerp and other insects are numerous on
blue gums they damage trees severely, irrespective of
the presence of bell miners.
Parasites. Minute wasps parasitize nymphs
under the lerp. The wasp larva develops within
the nymph and eventually pupates into a distinct
dark black pupa under the lerp. Holes in lerp
coverings (exit holes) indicate parasitism.
Bluegum psyllid in California is controlled by a
parasitoid Psyllaephagus pilosus from Australia.
Resistant/Tolerant varieties. In lerp-prone
areas of Australia resistant or tolerant species and
provenances of eucalypts is the only viable long term
strategy. Trees produced vegetatively or selections of
seedlings from resistant parent trees may be used for
planting, rather than seedlings from parents of
unknown resistance. Establishment of seed orchards
of resistant stock as a source of improved seed is a
long term option.
Susceptible species vary according to the
region and include Swamp mahogany
(E. robusta), Flooded gum (E. grandis),
Mahogany gums (E. botryoides, E. robusta),
River red gum (E. camaldulensis), Forest red
gum (E. terecornis), Yellow box (E. melliodora),
and Blakely’s red gum (E. blakelyi).
Insecticides.
Young eucalypts during establishment may
be protected by insecticide/fertilizer in tablet
formulation applied at planting.
Small trees < 3 m high. As the protective lerp
covering makes contact sprays ineffective,
systemic insecticides may be applied at the first
sign of infestation. Wetting agents improve
effectiveness. Foliage applications may disrupt
natural controls temporarily; also there is often
rapid re-infestation during outbreaks.
Timing. Only treat severe infestations. When
damage is noticeable it is usually too late to take
effective action. Apply insecticide when new
foliage has developed and lerps seem to be
increasing. One application per season may give
effective control for 6-8 weeks or longer if isolated
trees are treated (re-infestation is slow, adults do
not fly far). Insecticides are not a long term
solution.
Stem injection is effective for large trees.
What to use?
SMALL TREES (less than 3 metres)
Foliage sprays, eg
Group 1B, eg Rogor (dimethoate)
Group 4A, eg Confidor (imidacloprid); Crown (acetamiprid)
Soil treatments eg
Group 4A, eg Initiator (imidacloprid/fertilizer)
LARGE TREES
Foliage sprays, eg
Group 1B, eg Rogor (dimethoate)
Stem injection, eg
Group 1B, eg Rogor (dimethoate)
When and how to apply?
Foliage sprays, at first sign of infestation. Add a wetting
agent.
Initiator is for use in the establishment of young
eucalypt plantations by providing enhanced growth and
extended protection against damage by caused by
various insect pests including psyllids.
Foliage sprays. Only councils and arborists have
suitable equipment to spray large trees.
Stem injection. A systemic insecticide is injected into
the sap stream near the base of the tree and is carried to
the upper crown which is then taken up by feeding
psyllids. Permits may be required for stem injection.
Insects and allied pests - Hemiptera (bugs, aphids, etc) 159