PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
‘Overwintering’
As larvae in galls on the host plant.
Spread
Adults are poor fliers, but are assisted by wind.
By the movement of infested cuttings and plants.
Conditions favouring
Mild winters, proximity to existing infestations in
coastal districts of NSW and Qld. They are not a
problem in cold tableland climates.
Management (IPM)
Are you a commercial grower or home gardener?
1.Plan for your situation after obtaining advice from
your local department of agriculture.
2.Crop, region. Not a wide distribution.
3.Identification of pest, not difficult, must be
confirmed. Consult a diagnostic service (page xiv).
4.Monitor and record damage and/or parasitism
(page 39), eg
Monitor stems for citrus gall wasp once during
winter by examining 3-5 branches (30 cm long) from
20 randomly selected trees in a 1-5 ha block.
Monitor for parasitism in crop by collecting say
2-3 galls from each of 10 trees in a block in late
August, keeping them in plastic container with a
fine mesh lid. Gall wasps will emerge first about
10 days later, Megastigmus (if present) will emerge
for 2-4 weeks. The number of trees from which
samples should be taken depends on the block size
and history of infestation.
Yellow sticky traps attract wasps and other insects.
5.Threshold is determined in some areas by
legislation. Outside these legal obligations how much
serious damage, weakened trees can you tolerate
economically or aesthetically?
6.Action/Control. Carry out measures prescribed by
legislation. Otherwise biological control starts when
no parasites have emerged by mid-October. Either
release Megastigmus when 33% or more branches are
infested with 1 or more fresh galls and forego
spraying or apply a recommended pesticide between
the last week in November and the first week in
December, if there is a serious infestation.
7.Evaluation. Review your current program, assess
success of techniques and recommend improvements
if necessary. Evaluate sanitation procedures and
consider planting less susceptible varieties/crops.
Control methods
Legislation. There is a legal responsibility in
some areas of Australia where citrus gall wasp is a
‘proclaimed pest’, to carry out prescribed controls.
Sanitation.
Home gardeners. Because adults emerge
from galls in spring, all galls must be removed
by the end of August at the latest and burnt,
before wasps emerge to lay eggs in new shoots.
Table 18. Citrus gall wasp – Some insecticides.
Commercial growers.
– All galls from all the trees in one locality should be
removed at one time. Wasps are not strong fliers
and prefer to develop in the trees on which they
themselves developed.
– Cut off plants at ground level. Heavily galled trees
will benefit from a heavy pruning during winter.
– Burn all the removed growth in a manner which
kills all citrus gall wasps present in the growth.
– Destroy all regrowth not older than 2 years from
the plants within 21 days of appearance.
– Regular inspections of nurseries known to be
infested have prevented the wasp from becoming a
pest of commercial orchards.
– Do not allow shoots to develop on rough lemon, or
Troyer Citrange rootstock in the orchard to become
heavily infested with citrus gall wasp.
Biological control.
Natural controls. Citrus gall wasps may be
killed by heat or ants (Pheidole spp.) as they
emerge. Native wasps (Megastigmus spp.)
parasitize gall wasp larvae and may be trapped in
galls, unable to emerge.
Wasps for purchase. Wasps (Megastigmus
spp.) lay eggs in over 90% of gall wasp eggs in
young twigs resulting in smaller and fewer galls.
List of suppliers www.goodbugs.org.au/
Resistant varieties.
Avoid planting large areas of susceptible
varieties where citrus gall wasp is a pest.
Citrus gall wasp is more common in grapefruit
(most susceptible), orange and lemon. Mandarins
are least susceptible.
Plant quarantine.
Commonealth. Gall wasp (B. muli) occurs in
Papua New Guinea. If introduced into Australia
it could become a pest of limes.
Regional quarantine. The wasp is a problem
in Qld and northern NSW citrus areas and is
believed to have been introduced to Sunraysia
from infected budwood. Areas may be
Declared Quarantine Areas and any owner or
occupier of land on which infested trees are
growing may be required to treat specified citrus
trees in a prescribed manner. Check local
requirements.
Pest-tested planting material.
Only purchase and plant gall wasp-free budwood
and nursery stock.
Physical & mechanical methods.
Yellow sticky traps. Insectrap is a non-toxic,
sticky, yellow, cylindrical trap that attracts and
kills adult citrus gall wasps for 3-4 months,
reducing populations; it may attract bees and other
insects. The trap is weatherproof and waterproof.
The attractant within the trap is food-based.
Insecticides.
For home gardeners there is no practical
chemical control.
In commercial orchards, spray susceptible
grapefruit and mandarins with an appropriate
registered chemical when citrus gall wasp eggs
have hatched and before woody tissue has started
to form around the larvae, usually early December.
Timing of pesticide application is critical.
What to use?
Group 1B, eg Supracide , Suprathion (methidathion)
DANGEROUS POISON
When & how to apply?
Commercial growers only. Only to be applied by
licensed operators. Toxic to parasitic wasps
(Megastigmus) in IPM programs.
122 Insects and allied pests - Hymenoptera (ants, bees, sawflies, wasps)