PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
4. Monitor for mealybugs when they are known to be
active and record findings. Check roots of wilting
plants, for the presence of mealybugs, sooty mould,
honeydew, ants. Also monitor for biological control
agents. If using an IPM program it will tell you when
and where to look, what and how to monitor, eg
adults, crawlers, main parasites and predators. Desire
Sticky traps are available for citrophilous mealybug:
http://insense.com.au/products.htm
5. Thresholds vary according to the crop and method of
proposed control. Some pest scouts prefer to use a lower
action level early in the season depending on the variety,
populations of mealybugs and predators, and degree of
parasitism. How much damage can you accept?
6. Action. Take appropriate action if threshold is reached.
7. Evaluation. Review your program and recommend
improvements. Monitor trees and bins after treatment,
compare results with the previous season.
Control methods
Cultural methods.
Adequate irrigation helps reduce effects of
infestation by replacing sap lost to sucking insects.
Maintain plant vigour.
Cover crops decrease temperatures, increase
humidity in summer favouring natural controls.
Sanitation.
Discard severely infested small plants of little
value in greenhouses and houses.
Prune off badly affected sections of plants.
Minor infestations on house plants may be
picked off and killed or removed by dabbing with
a small brush or cotton bud dipped in methylated
spirits. This is tedious and time-consuming, will
not eradicate them and may break stems and
foliage of soft-foliaged plants. Plants may be
washed with or dipped upside down in warm
soapy water and then rinsed in clear tepid water.
Large plants may be sponged.
Sooty mould in the navels of mature oranges is
not easy to remove by washing before packing.
Throughly disinfest recycled pots to avoid
transferring eggs or nymphs from crop to crop.
If root mealybugs, thoroughly disinfest nearby
gravel including beneath plastic and weed mats.
Biological control.
Natural controls are not always effective.
Parasites and predators are discouraged by dust and
ants (attracted by honeydew) and some pesticides.
– Predators include lacewing larvae (Chrysopa sp.,
Oligochrysa lutea), mealybug ladybird.
– Parasites include various wasp parasites, eg
Anagyrus, Leptomastix.
– Root mealybugs are underground and not so
accessible to natural controls.
Commercially available.
– Main parasite is the small wasp (Leptomastix
dactylopii) which may be reared or purchased. Two
parasites (Coccophagus gumeyi and Tetracnemoides
brevicornis) have been released to suppress
citrophilous mealybug.
– Main predator is the mealybug ladybird
(Cryptolaemus montrouzieri) which is black and red,
3.5 mm long, lays its yellow eggs singly in mealybug
egg sacs or near clusters of mealybugs. Other
ladybirds include Rhyzobius ruficollis and Scymnus
spp. Larvae of the cecid fly (Diadiplosis koebelei) and
lacewings (Mallada spp.) also feed on mealybugs.
– List of suppliers www.goodbugs.org.au
Resistant/Tolerant varieties. Some plants
are very susceptible, eg African violet, citrus, ferns.
Plant quarantine. Nurseries growing very
susceptible species should quarantine and examine
new stock brought in from external sources.
Keeping mealybugs out of nurseries is preferable to
controlling them once they are established.
Pest-tested planting material.
Only propagate from and purchase mealybug-free
stock. Examine all stock plants.
Insecticides. Mealybugs are difficult to control
with insecticides because they feed in protected
places, are covered with water-repellent wax and lay
large numbers of eggs which develop quickly under
ideal conditions (see also page 170).
Glasshouses may require regular treatments.
Apply insecticides to crawlers - the arrival of ants
indicate crawlers are about! Use a hand lens to
identify them so you can initiate control measures.
Control ants if present outdoors in spring.
Systemic insecticides are generally more
effective than contact ones.
Apply high volume sprays to fully wet canopy,
application must be thorough.
If mealybugs are on roots of plants in pots, wet
soil in pot thoroughly the night before treatment
to lesson chance of root damage. Place pot in basin
and allow insecticide solution to soak in.
Use enough liquid to wet the complete root zone.
Table 30. Longtailed mealybug – Some insecticides.
What to use?
HOUSE PLANTS
Only use sprays labeled for indoor use.
GLASSHOUSES
Seek advice
OUTDOORS
Insecticides registered for mealybugs generally:
Group 1A, eg Bugmaster (carbaryl)
Group 1B, eg Rogor (dimethoate); maldison;
Folimat (omethoate)
Group 3A, eg pyrethrins, Baythroid (cyfluthrin);
Procide , various (bifenthrin)
Group 4A, eg Confidor ,various (imidacloprid);
Maxguard (acetamiprid);
Sumarai (clothianidin)
Group 16, eg Applaud (buprofezine)
Spray oils, eg certain petroleum, paraffinic and
botanical oils
Soap sprays, eg BugGuard , Natrasoap
(potassium salts of fatty acids)
When & how to apply?
Take plants outside for treatment unless label advises otherwise.
Oils may injure many indoor plants, especially maiden hair ferns.
Regular treatments may be required. Outdoors avoid spraying
mealybug-prone plants for other pests and diseases (this will kill
any natural controls). Control ants. Consider spot spraying.
Only after monitoring and if natural enemies cannot cope with
infestation.
Contact sprays are only effective if mealybugs are actively
moving over the plant. Adult mealybugs that have developed their
waxy covering are difficult to kill with contact pesticides. Contact
sprays are devastating to all beneficials. Contact sprays can be
effective against crawlers.
Systemic sprays give good control of adult mealybugs that are
feeding. Once they have stopped feeding it is too late to control
them. Some systemic sprays are not so harmful to some beneficials.
Spray oils are only effective against young stages of mealybugs
but are less harmful to beneficials than many insecticides.
Loosens sooty mould. Oil sprays smother nymphs.
162 Insects and allied pests - Hemiptera (bugs, aphids, etc)