PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Control methods
Control of scarab grubs is difficult and often not
economic. Good culture is a good start.
Cultural methods. Healthy vigorous turf can
support many grubs without apparent damage.
Avoid frequent light watering that may
encourage egg laying and shallow-rooted turf
which will not tolerate surface drying. Remedy
soil compaction, the most common cause of
water run-off, which prevents water penetration.
Fertilize when turf is actively growing, eg
spring/autumn. Fertilize and/or water pasture if
economic. Reduce stocking pressure.
Core turf to aerate lawn, aid water penetration.
Lawns containing clovers are less severely
damaged, as grubs prefer to eat grass roots.
For crops other than turf, a period of fallow
between ploughing and planting can be beneficial.
Thorough preplant cultivations expose larvae
to birds and mechanically injure and kill them.
Avoid planting new ground with susceptible
crops, eg maize, after pasture in areas with a
known history of scarab grub infestation.
Check the top 10-15cm of soil before
planting for scarab grubs and other pests.
Cut lawns at recommended height.
Close or irregular cutting reduces turf vigour by
removing too great a proportion of the leaf blade,
which is the major food-producing part of the
plant and exposes the crown to excessive drying
out and damage. Bare patches may develop.
– Mow turf frequently removing only l/3 rd of the
height of the existing grass. Find out the correct
mowing height for the turf you have.
– If turf is allowed to grow too tall, only cut a few
centimetres of the top and cut again a week later.
Sanitation.
Remove litter on the soil surface to reduce hiding
places for adults during the day.
Use clean potting mix to prevent larvae/pupae
from being introduced.
Avoid spreading infested soil or potting mix
around the property.
Before planting remove volunteer plants and
trash through cultivation to maximize
mechanical injury to larvae.
Destroy any infested plant material and debris.
Biological control.
Natural controls.
– Predators. In wet turf and pasture, currawongs,
starlings, other birds, bandicoots and ground beetles
feed on larvae close to the surface or exposed by
cultivation. Birds, robber flies adults and some
species of possum will attack adult beetles.
– Parasitic wasps and flies lay eggs in larvae.
Wasps feed on nectar from flowers.
– Diseases caused by viruses, bacteria, fungi and
nematodes infect larvae. If grubs are present and
near the surface, watering during the day or early
evening may increase activity of these diseases.
– Prolonged drought, wet or extremely high soil
temperatures at egg laying kills many eggs.
– Viral, bacterial and fungal disease organisms are
being researched for adult scarab beetles.
Commercially available. products include:
– Nematodes. Heterorhabditis zealandica controls
African black beetle, Argentine scarab, Argentine
stem weevil, black-headed cockchafer, red-headed
cockchafer, bill bug weevil.
www.ento.csiro.au/biocontrol/scarabs.html
– Biocane TM Granules (Metarhizium sp.) controls
greyback canegrub (Dermolepida albohirtum).
Tolerant varieties.
Roots of some grasses, eg tall fescue, regenerate
more quickly than some other grasses. Clover is
less severely damaged.
Plant quarantine.
AQIS. NZ grass grub (Costelytra zealandica) is
a serious pest of pasture and crop plants in NZ. It
could enter Australia as adult beetles in cargo
and goods freighted to Australia from NZ.
Pest-tested planting material.
Plant clean plant material from properties known
not to be infested.
Check root area of incoming stock.
Physical & mechanical method.
Overseas a nail-studded roller behind mowers
injures grubs feeding close to the surface and
may encourage secondary infection of grubs.
Insecticides. If chemical insecticides are to
successfully control larvae then:
Soil drenches will be needed.
Apply during Jan-Feb when grubs are small, close
to soil surface feeding on organic matter, body fat
is minimal and before obvious damage.
Treatment carried out when turf is damaged,
usually late in autumn, leads to poor results, as
grubs, feeding deeper in soil, contain larger
quantities of fat which may absorb some of the
chemical preventing them from being killed.
Select insecticides non-toxic to birds.
Target adult beetles by spraying late in the day or at
night to control species active at that time.
Failure to control scarab grubs is usually due to
poor timing and/or methods of application.
Spring applications for residual pesticides, control
of scarab grubs may suppress earthworms and some
predatory invertebrates but effects short-lived.
Table 14. Scarab grubs – Some insecticides and biocontrol agents.
What to use?
SOIL TREATMENTS (LARVAE)
Group 1A, eg carbaryl (not on food-producing plants in the home garden)
Group 1B, eg various (chlorpyrifos)
Group 3A, eg Baythroid Turf (cyfluthrin); Brigade ,
MaxGuard (bifenthrin); Tempo (beta-cyfluthrin)
Group 4A, eg Confidor , Confidor Guard Soil Insecticide,
Merit (imidacloprid); Initiator (imidacloriid +
fertilizer); Meridian (thiamethoxam)
Group 28, eg Acelepryn (chlorantraniliprole)
Biocontrol agents, eg Nematode (Heterorhabditis
zealandica); Biocane TM Granules (Metarhizium sp.)
Others, eg Eucalyptus oil/Melaleuca oil
When and how to use?
Preplant treatment may be necessary for some
crops, eg strawberry.
Turf. Where scarab grubs are a problem apply in
January after young grubs hatch out from Decemberlaid
eggs. Check local dates for application.
– Before treatment mow turf and water lightly and
to ensure insecticide reaches larvae in soil.
– After treatment water heavily to carry chemical
into root zone and reach larvae 25 mm deep and
avoid poisoning ducks. Check how long the
treatment is effective for.
Establishment of young eucalypts plantations.
Initiator provides extended protection against damage
caused by scarab larvae and adults, and other insects.
Ornamentals in pots. Seek advice. Permits may
be required.
110 Insects and allied pests - Coleoptera (beetles, weevils)