PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Spread
By thrips. which are poor fliers and spread by
wind, on plants, people or on equipment, eg
Western flower thrips (WFT) (Frankliniella
occidentalis), onion thrips (Thrips tabaci), common
blossom thrips (F. fusca) and tomato thrips (F.
schultzei). More species overseas.
– WFT is the most efficient vector of TSWV
and can feed on a many ornamentals, vegetables and
weeds (pages 138, 139).
– Only nymphal stages of WFT can acquire the
TSWV, while only adults can transmit it. WFT
nymphs must feed on an infected plant for as little
as 15 minutes to become a carrier. Having picked
up the virus, the virus moves through the gut and
into the salivary glands, after 5 days of incubation
they can transmit it during feeding to healthy plants
for the rest of their adult life (30-45 days). Adult
WFTs cannot transmit the virus to their offspring
(other thrips species may vary slightly).
– Not all WFT are infected with TSWV.
By vegetative propagation from infected
plants.
Rarely by seed, except broad bean.
Not by contact between plants.
Not by pollen.
Movement of infested plants, seedlings.
Conditions favoring
After hot dry weather, thrips migrate to ornamental
and vegetable crops when the weed hosts on which
they have been breeding and feeding have matured
and dried out.
High thrips numbers.
Overlapping crops, the carrying over of long term
plants and parent stock plants that might act as
reservoirs for thrips and/or the virus.
Management (IDM)
Are you a commercial grower or home gardener?
Management guides are available for some viruses
(Persley et al 2008).
1.Obtain/prepare a plan that incorporates
information from the National Strategy for Management
of WFT and TSWV and/or State/Territory brochures.
2.Crop, region, season, life cycle. Be aware of all
these and the extensive host range.
3.Identification may be difficult and complicated.
Expert help may be needed so consult a
diagnostic service (page xiv).
4.Monitor. Know when, where, what and how
to monitor, early detection is vital.
Check sticky traps for signs of thrips.
Symptoms of abnormal leaves and growing points.
Flag indicator plants, eg petunias, with blue or
yellow non-sticky cards to attract thrips.
5.Threshold. There may be a nil threshold in some
commercial crops and the vector may be a targeted
pest in WFT-free zones. Growers may have to set
their own economic threshold on some crops.
6.Action/control depends on thresholds and includes
weed control, etc. Home gardeners may rogue affected
plants and not use infected plants for propagation, they
should not attempt to control thrips by spraying.
7.Evaluation. Review program and recommend
improvements if required. Continue to monitor thrips
in the crop and surrounding areas.
Control methods
There is no cure. for infected plants in the field.
Minimize losses from TSWV by eliminating TSWVinfected
plants and controlling thrips vectors.
Cultural methods.
Do not grow tomatoes near flowers crops or weeds
which act as alternative hosts for vectors.
Early plantings of tomato are affected more
seriously than later plantings.
Avoid overlapping or sequential planting of
susceptible crops.
Use a fallow break or plant a crop that is not
TSWV-susceptible between regular crops.
Home gardeners can plant excess tomato seedlings
to allow for losses due to TSWV.
Sanitation.
Rogue or spray and destroy TSWV-infected crops
as soon as observed, especially if young crops are
growing nearby. Symptomless hosts cannot be
rogued and so act as a source of virus.
Dispose by burning or burying (maybe spray
first to ensure that any thrips infected are killed).
Destroy infected stock plants.
Destroy weeds harbouring thrips and TSWV
around crops (at least a 10-25m strip), eg
sowthistle. Most weeds are symptomless.
Plant new susceptible crops as far away from a
source of infection as possible.
Keep property free of crop residues and volunteer
crop plants, eg corms, tubers, bulbs.
Clean and sterilize greenhouses between crops.
Place sticky traps in the empty greenhouse to detect
any remaining adults.
Biological control.
Thrips vectors have many natural controls including a
predatory mite (Typhlodromis montdorensis) and
lacewings (Mallada spp.) which are general predators.
(page 139). List of suppliers www.goodbugs.org.au
Resistant varieties.
Use TSWV-resistant varieties when possible, these
may be available for tomato and capsicum.
If possible avoid planting varieties of crops that are
most likely to carryover TSWV.
Most tomato varieties are susceptible to TSWV.
Resistant varieties are being bred.
Resistance to thrips may assist.
Plant quarantine.
WFT, a vector of TSWV, is a targeted pest in some
districts, eg the Toolangi Plant Protection District.
Check all incoming plants, eg cut flowers for thrips
and TSWV, quarantine in an insect-proof area to
determine thrips and TSWV status.
Disease-tested planting material.
TSWV is not seedborne, seed from diseased crops
can be saved (except broad bean). You can grow
your own seedlings which will remain free if kept
away from thrips with access to infected plants.
Plant only certified virus-tested planting material
(seed, propagation material) if available.
Only propagate from disease-tested stock plants.
Keep stock plants separate from crop plants.
If buying check that plants are free of thrips.
Physical & mechanical methods.
Exclude thrips from greenhouse crops by screening
with a fine thrips-proof mesh (may reduce airflow).
Viricides, insecticides.
There are no registered pesticides which will
cure a plant of virus infection in the field.
Use sticky traps to measure vector activity and
apply insecticide when populations are above the
recognized action threshold (page 140).
Because TSWV is more serious in young plants, it
may be worthwhile spraying commercial seed or
cutting beds to control thrips.
Regular insecticide applications to field crops and
surrounding crops and weeds to control thrips
during periods of thrips activity (as determined by
monitoring), will reduce numbers of infected plants.
Anti-transpirants and spray oils may repel thrips.
Follow Insecticide Resistance Management
Strategies on labels (page 140).
288 Virus and virus-like diseases