PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Conditions favouring
Soil or media which is continually wet, over
watered, poorly drained. Highly moistureretentive
potting mixes.
Persistent pest in protected nurseries.
Soil or potting media rich in organic matter.
Low light, high humidity, misting systems.
At 24 o C reproduction is continuous.
Management (IPM)
Are you a commercial grower or home gardener?
1. Prepare a plan if fungus gnats are an ongoing
problem which includes better management of media,
drainage, humidity and fertilizers.
2. Crop, area. Mark plants or areas where control is
required. Proper application and use of nematodes
will vary with crop and production system.
3. Identification of adults and larvae must be
confirmed. Consult a diagnostic service if necessary
(see page xiv). Locate main breeding areas, be familiar
with its life cycle, method of spread, etc.
4. Monitor pest and/or damage and record results which
will indicate when peak populations occur (page 39).
Trap adults on yellow sticky traps.
Monitor maggots by placing potato discs on moist
potting media. Larvae are attracted to the discs and
tunnel underneath or into the discs.
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 for crops at risk?
6. Action. Implement appropriate treatment, when any
threshold has been exceeded. Early treatment prevents
damage. If using nematodes apply initially at planting
and shortly thereafter or if yellow card counts are
< 50/trap/week (guide only).
7. Evaluation. Continue monitoring to ensure control
measures have been effective. Records compiled
over several seasons help develop control thresholds
relevant to the month and stage of crop growth.
Control methods
Cultural methods.
The only permanent cure is to avoid overfertilizing
and overwatering. Improve drainage.
Allow media to dry out as much as possible
without injuring plants before watering will kill
many maggots. Maggots do not like dry media.
Avoid using potting media high in organic matter
such as peat. Plants may need to be repotted using
less organic matter.
Avoid storing media where it can get wet and
attract adult flies. They will colonize it and then
enter the production cycle.
Shore flies are controlled in a similar manner.
Sanitation.
Remove and destroy badly infested containers.
Keep areas below benches, walkways, corners
and surrounding areas free of pools of water,
fertilizer, spilled potting media, unwanted pot
plants, plant debris and weeds. Disinfect
surfaces; remove algae (shore fly).
Biological control.
Natural controls include predatory mites,
beetles and parasitic wasps.
Commercially available agents. Many
variables can affect the performance of biocontrol
agents, eg pesticides used for other pests,
improper storage and incorrect use.
List of suppliers www.goodbugs.org.au/
– Nematodes (Steinernema spp.) are applied as a
drench or spray drench to growing media after
planting. The nematodes seek out natural openings
on the fungus gnat larvae present among the roots
of plants. When inside they release bacteria which
causes septicaemia in the maggots. After 2 weeks
the nematodes have multiplied inside the maggots
which rupture releasing more nematodes to search
for more maggots. Store at 5 o c do not freeze.
Becker Underwood www.beckerunderwood.com/
Ecogrow Environmental www.ecogrow.com.au
50 MILLION
INFECTIVE JUVENILES
– Cybate , Vectobac (Bacillus thuringiensis var.
israelensis), bacteria which produce a crystalline
protein is registered for the control of mosquito
larvae and possibly could be useful in the future
against fungus gnat larvae.
– Predatory soil-dwelling mites (Hypoaspis sp.)
feed on larvae of fungus gnats. Introduce soon after
planting before fungus gnats become established.
– Predatory rove beetles (Dalotia (Atheta)
coriaria) feed on shoreflies in addition to thrips
and fungus gnats.
Physical & mechanical methods.
Vermiculite (50 cm) or sand on top of soil
discourages adult flies from egg-laying.
Sticky yellow boards trap adult flies.
Light traps also capture large numbers of flies.
Screening greenhouses to exclude adult flies.
Properly compost potting media to kill maggots.
Pasteurization of media, if practical.
Increasing light levels and ventilation reduce
favourable breeding conditions.
Insecticides.
Foliage sprays and dusts may control adult flies
while soil drenches control maggots (Table 6).
Compost-incorporated insecticides and insect
growth regulators (IGRs) have been used
overseas with good results. IGRs interfere with
molting of maggots killing them. More target
specific, not broad spectrum. Often have shorter
restricted-entry intervals. Choose one which does
not injure roots/plant bases.
Table 6. Fungus gnats – Some insecticides and bio-control agents
What to use?
TO CONTROL ADULTS
Group 3A, eg pyrethrins
TO CONTROL LARVAE
Group 1A, eg Mesurol spray (methiocarb)
Group 4A, eg Crown (acetamaprid)
Group 15, eg Dimlin Insect Growth Regulator (diflubenzuron)
Group UN, eg Azamax , Eco-neem , Neemazole (azarachtin)
Bio-control agents (nematodes), eg
Steinernema. feltiae, S. carpocapsae
When and how to apply?
Adult flies must be killed before egg laying.
Drench soil, potting mix or compost in which infested
plants are growing. Apply when larvae are first seen.
Drench media thoroughly.
76 Insects and allied pests - Diptera (flies)