PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Spread
By thrips flying assisted by wind. Larvae pick
up the virus during feeding, after which it is
replicated and circulated in the thrips’ body.
It can be successfully transmitted after only
30 minutes by (predominantly) adult WFT
during feeding to healthy plants for the rest of
their adult life (30-45 days).
Movement of infested plants, vegetative
propagation material, cut flowers, cuttings,
seedlings, runners, weeds.
Thrips may continually invade flowers from
surrounding areas.
Conditions favouring
Warm and moist springs and summers, optimum
temperature is 20-30 o C
Thrips numbers outside are lowest in winter.
Failure to allow a fallow break between
successive WFT-susceptible crops.
Management (IPM)
WFT is difficult to control once established. For
commercial growers:
1. Obtain advice from your State Dept. WFT
Coordinator (state website), on monitoring and
thresholds for different crops, eg Qld DPIF. 2008.
Thrips and Tospovirus: A Management Guide; NSW
DPI. 2007. Western FlowerThrips & Tomato Spotted
Wilt Virus. There is a National Strategy for the
Management of WFT.
2. Crop, region. National Strategies for Managing
WFT vary depending on the crop, eg field crops,
cucumbers, strawberry, ornamentals, greenhouses,
type of viruses spread, etc.
3. Identification is critical for effective control so
consult a diagnostic service (page xiv) if necessary.
Early detection and regular monitoring of WFT with
sticky traps, etc, is essential for effective control before
populations reach damaging levels (page 39).
4. Monitor for WFT in crops, greenhouses and sheds
using blue sticky traps, the following is only a guide:
– Record population trends on a chart. Continue
monitoring after any treatments.
– Know when to start monitoring, when to inspect
flowers and put out traps, etc.
– Crop inspection. Walk through and inspect the crop
regularly, count thrips in new buds and flowers, or
dislodge them by tapping flowers over a white tray. A
x10 hand lens is needed to identify them.
– Sticky blue traps attract thrips and some leafminers
(not beneficial insects), yellow cards attract many
other insects as well, eg thrips, whitefly, aphids,
fungus gnats, shoreflies. Hang traps just above or
within the crop, near green house doors, flowers and
young growth, and packing sheds. Adjust position of
traps so they are in the best place to catch thrips.
Inspect traps fortnightly or as recommended, replace
every 2 weeks or more frequently if they get dirty or
crowded with insects.
– Indicator plants, eg petunia (Calypso, Super Blue
Magic, Summer Madness) or fava beans, can be
placed in a greenhouse to detect for early TSWV
and INWV symptoms.
5. Thresholds are different depending on crop type and
quarantine regulations, designation of WFT-free
zones, etc. These are established thresholds and may
need to be complied with. Swiss work shows that if
sprays are only applied to chrysanthemum crops when
the pest level reached 20 WFT/trap/week, damage did
not exceed 5%.
6. Action/control depends on delaying development
of resistant WFT and whether an insecticide permit is
needed before spraying with an appropriate chemical.
Continued and vigorous non-chemical control
including sanitation must be conducted at all times.
Release bio-control agents if appropriate. Thrips
programs need to be all year round.
7. Evaluation. Review IPM program. How successful
was it? Are improvements necessary? Continue to
monitor, record and assess your methods.
Control methods
Cultural methods.
If practical propagate or plant crops when thrips
numbers are low.
If possible roses and nursery stock should have
no leaves at the time of planting.
Grow and train crops so that good spray coverage
is easy to achieve.
New susceptible crops should be planted as far
away as possible from a source of infestation.
Avoid continuous cropping. Start thrips control
at the end of the previous crop or season.
– Consider a plant-free fallow period before
starting the next crop. Eliminate weeds/host plants.
– Heat empty greenhouse until temperature of
soil is about 30 o C for about 3 weeks, longer at
lower temperatures. This will allow thrips in the soil
to emerge as adults and starve in the absence of
food plants. Check for living adult thrips on traps.
When there are no thrips and any uprooted plants
are completely dry, plants can be removed from the
greenhouse. It may take between 2-4 weeks to dry
uprooted plants and kill all thrips.
– Some growers may apply a smoke or aerosol
after the second week to ensure all thrips are killed.
Sanitation.
Aim to identify and eradicate non-crop hosts of
WFT including weed hosts which not only serve
as hosts for thrips but for viruses (INSV, TSWV),
eg hanging baskets, etc.
Avoid carryover from one crop to the next by
removing prunings, unwanted blooms, remains
of previous crops and weeds.
Dispose of plant residues, eg plough in or burn
old crop debris, cover dump and waste sites and
place waste in black plastic bags, seal immediately
and leave in the sun to solarize (heat up).
Move from clean to infested greenhouses, never
from infested to clean areas unless clothes are
changed. Avoid wearing pale white, yellow or
blue clothing attractive to thrips.
Clean equipment after use in infested areas.
Roguing. Remove any plants with thrips or
symptoms of TSWV or INSW immediately.
Remove plants that attract thrips in garden
beds around production areas. Ideally have
10 metres bare ground such as asphalt around
greenhouses or closely mown grass. Do not plant
flowers or allow weeds to grow in this area, this
applies to hydroponic growers as well.
Biological control.
Natural controls include predatory mites, bugs,
parasitic wasps, eg (Ceranisus menes) and fungi,
eg (Beauveria bassiana, Verticillium lecanii).
Commercially available., eg
– Predators. List of suppliers www.goodbugs.org.au
Predatory mites, eg Amblyseius montdorensis
and Neoseiulus cucumeris suppress low
populations of WFT and other thrips in protected
areas, eg greenhouses. Mainly attack 1 st stage
nymphs, so large numbers and frequent
introductions are needed for successful control.
Provide adequate ventilation and choose
insecticides carefully. If thrips are absent mites
feed on pollen.
Soil-dwelling mite (Hypoaspis miles) is a
general predator feeding on thrips pupae near
the soil surface, fungus gnat eggs, larvae and
pupae, nematodes, etc.
Pirate bugs (Orius spp.) feed on larvae and
adult thrips, also excess pollen in the absence of
thrips. May be difficult to establish.
Lacewings. Mallada signata feeds on thrips,
aphids, mealybugs, whiteflies. Chrysoperia sp.
preys on WFT adults, larvae can be purchased.
Insects and allied pests - Thysanoptera (Thrips)
139