PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
‘Overwintering’
On host plants, pupae may be seen in the tunnels
on the undersurface of the leaf.
Spread
By adults flying, by propagation, eg cuttings from
infested plants and by the movement of infested
plants, plant parts, infested plant debris.
Conditions favouring
Cool humid weather during late winter, spring and
early autumn. Fine meandering lines initially
appear on leaves during late winter and spring.
There seem to be more of a problem in coastal
areas such as Melbourne and Sydney.
Management (IPM)
Are you a commercial grower or home gardener?
1.Access/prepare a plan which fits your
situation based on previous records of cineraria
leafminer damage to susceptible varieties.
2.Crop, region. Know and mark all susceptible
varieties in your area/garden which may require
treatment.
3.Identification of pest must be confirmed by a
diagnostic service if necessary (see page xiv).
4.Monitor. Examine leaves for mines and larvae
during late winter and early spring depending on the
region (page 39). Record your findings.
5.Threshold. How much damage can you accept?
Have any thresholds been established? If so, what are
they, eg economic, aesthetic? Do you need to calculate
your own threshold? Commercial growers often have
a threshold of appearance of the first mines. This will
vary with season and region.
6.Take appropriate action when any decided
threshold is reached. Prune out any infested leaves and
apply insecticides as soon as mines are detected and
when maggots are still mining in leaves but have
not pupated. Repeat applications may be required
until warm weather arrives. Record treatment dates,
etc. Home gardeners usually settle for sanitation
measures. Remember if pupae have formed in the
leaves it is too late to spray.
7.Evaluation. Review IPM program to see how well
it worked. Recommend improvements if required, ie
growing less susceptible varieties. Continue to
examine leaves to ensure treatment has been
successful or there is a need for further treatment.
Control methods
Cineraria leafminer can be difficult to manage.
Cultural methods. Fertilize and water
affected plants. Overseas adding potassium silicate
to fertilizer mixes with potted chrysanthemums
(200ppm or higher) saw a significant reduction in
leafminers emerging from treated plants versus the
control. This may be a good cultural tool for
suppressing leafminers.
Sanitation. Occasional shoots which are
infested may be pruned off and destroyed in such a
way that adult flies cannot emerge from the pupae
within the leaf tissues. All prunings from infested
plants should be destroyed. Control weeds and
volunteer hosts.
Biological control. Overseas, parasitic
wasps may control cineraria leafminer on
chrysanthemum. Check with Australasian
Biological Control for possible biocontrol agents.
List of suppliers www.goodbugs.org.au
Resistant varieties. Varieties vary in
resistance. The florists chrysanthemum
(C. sinense) seems to be resistant. Margarite
chrysanthemums (Chrysanthemum frudi) and
shasta daisy (C. maximum) are susceptible.
Plant quarantine. There are other leafmining
insects which are major pests of chrysanthemum
and other Asteraceae overseas. Serpentine
leafminer (Liriomyza trifolii) is probably the most
important. Chrysanthemum and gypsophila
imported from areas where it occurs are subjected
to mandatory treatment. Other leafminers overseas
include L. huidobrensis, L. sativae and
Amauromyza maculosa.
Pest-tested planting material. Avoid
taking cuttings from infested plantings. If this is
unavoidable, select plants for propagation which
are apparently damage-free.
Insecticides.
See Table 5 below.
Table 5. Some insecticides for leafminers generally.
What to use?
FOLIAGE SPRAYS
Group 1B, eg Rogor (dimethoate)
Group 4A, eg Confidor Guard Soil Insecticide
(imidacloprid) - citrus leafminer on citrus
Group 5 eg Success 2 Naturalyte Insect Control (spinosad)
See also page 128
Spray oils, eg petroleum oils, paraffinic oils, botanical oils
Remember, check the plant and the leafminer the
product is registered for use on
When and how to apply?
If using a spray:
Use a penetrant or systemic chemical to kill larvae
inside leaves.
If maggots have pupated, it is too late to spray. Hold
several leaves up to the light, if most tunnels have a
small round hard pupa at the end, then pupation has
taken place and spraying is not effective.
Several sprays at approximately weekly intervals
may be necessary if larvae are still active and further
infestations occur, ie in late winter and early spring if
weather is cool and wet.
Ensure that both sides of the leaves are wetted
thoroughly with spray.
74 Insects and allied pests - Diptera (flies)