PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
‘Overwintering’
In coastal areas plague thrips are present in varying
numbers throughout the year but it is only in spring
and early summer that they cause plant damage.
Spread
Adult thrips fly readily within a crop.
They may be carried long distances by wind and
migrate to crops in large numbers from a wide
range of weeds, grasses, other flowering plants.
Conditions favoring
Commonly found in huge numbers in and/or
near blossoms in spring. Crops at greatest risk
during flowering and podding.
Serious spring outbreaks follow mild winters,
which allow survival of the hibernating thrips,
preceded by autumns with above average rainfall.
If these conditions are followed by a dry sunny
spring with abundant flowers on capeweed and
other hosts, thrips build up on these hosts then,
when their flowers dry off, migrate to crops,
causing severe outbreaks of thrips in spring and
early summer.
A spring with alternating warm and cold periods
bring thrips generations into line. During warm
days millions of the tiny thrips appear suddenly,
and often disappear next day in a cold change.
Management (IPM)
Are you a commercial grower or home gardener?
1.Prepare a plan that fits your situation. Obtain
leaflets on plague thrips control for you local area.
See western flower thrips (WFT) (page 139).
2.Crop, region. Recognize variations.
3.Identification of pest must be confirmed. Consult
a diagnostic service if necessary (page xiv).
4.Monitor thrips on flowers during flowering on crops
and weed hosts as for WFT (page 139). Otherwise open
buds and examine flowers for presence of thrips, control
if more than 4-6 per flower. Flowers could be stored in
70% alcohol to dislodge thrips and prevent escape; they
can be identified and counted later.
5. Threshold. How much damage can you accept?
What is your threshold? Economic, aesthetic?
With fruit it is usual to commence applications
when there are 4-8 thrips per flower or if the thrips
look numerous on capeweed. As an example, in
apple, 6-8 thrips per blossom during pink to full
bloom following a warm dry spell, may indicate
potential for reduced fruit set.
On ornamentals like roses, it is usually necessary
to commence applications as soon as thrips start to
appear in buds or as soon as petal colour is visible.
6.Action/Control. Take appropriate action when any
threshold is reached. Plague thrips can cause total loss
of some fruit crops, eg raspberry, if not controlled.
However, damage on some plants, eg grapevines,
citrus, plum, pears, is not always economic and
therefore control may not be necessary.
7.Evaluation. Review IPM program to see how
well it worked. Recommend improvements if required.
Control methods
Control of plague thrips in blossoms is difficult
because eggs are inserted within the plant tissues
and nymphs and adults feed and shelter within
opening buds out of reach of insecticides.
Cultural methods. Heavy rain or overhead
irrigation can reduce infestations spectacularly but
may damage flowers. If the soil surface is compacted
adult thrips cannot emerge from pupae in soil.
Vigorously growing crops can usually compensate
for flower abortion.
Sanitation. In the home garden, remove and
destroy infested spent blooms of roses by placing
in a plastic bag with the neck secured and leaving
in sun for a few days. Remove weeds especially
flowering ones, eg Paterson’s curse, wild mustard.
Biological control.
Natural controls include fungal diseases
(Metarhizium spp., Entomophora spp. Beauveria
spp., Paecolomyces sp.). Although there are some
predators, eg lacewing larvae, mites, thrips, and
some parasites, eg wasps, their effect can be
insignificant compared with that of the weather.
Conserve pirate bugs, lacewing larvae and
ladybirds which prey on thrips.
Biocontrol agents which can be purchased.
– A soil mite (Hypoaspis miles) feeds on thrips
pupae near the soil surface.
– Predatory mites Neoseiulus cucumeris and
Typhlodromus montdorensis feed on thrips larvae.
List of suppliers www.goodbugs.org.au
Physical & mechanical methods.
In greenhouses thrips-screens on vents and doors
prevent their entry (page 140).
Insecticides. When treating thrips in flowers,
aim to not only kill thrips present but also to
prevent re-infestation (page 140).
Table 23. Plague thrips – some insecticides.
What to use?
TOXICITY OF INSECTICIDES TO BEES
Most insecticides are toxic to some degree to bees. Follow label
instructions regarding application. Information on the toxicity
of insecticides to honey bees is available from local State/
Territory Depts., eg Pesticides – A Guide to their Effects on
Honey Bees. NSW DPI Primefact 148 (2006).
BLOSSOM TREATMENTS
Group 2C, eg Regent (fipronil)
Group 3A, eg pyrethrin, Baythroid (cyfluthrin),
Mavrik (tau-fluvalinate); Talstar (bifenthrin),
Sumi-Alfa Flex (esfenvalerate); Titan , various
(cypermethrin)
Group 4A, eg Crown , Procide (acetamiprid)
Others, eg Beat-a-Bug (chilli/garlic/pyrethrin/piperonyl butoxide)
When and how to apply?
Avoid spraying in full bloom, danger to bees.
If unavoidable carefully consider the toxicity and
formulation of the pesticide to be used.
Any spraying should be done late in the evening
when bees have returned to hives.
For effective control it is necessary for the
insecticide to have a residual activity of 2-4 weeks.
The more quickly the insecticide breaks down, the
more frequently it must be applied.
Follow label directions but usually 2 applications are
necessary - about 2 weeks apart. The 2 nd spray will kill
nymphs which have hatched from eggs which were
unaffected by the 1 st spray and adults which have
emerged from pupae in the soil since the 1 st spray.
Insects and allied pests - Thysanoptera (Thrips)
137