PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
‘Overwintering’
Usually in the pupal stage which is attached by its
tail to the food-plant or nearby object.
Spread
By butterflies flying assisted by wind, strong fliers
may be found many kilometers from host plants.
Movement of infested host plants carrying eggs,
caterpillars or pupa.
Conditions favoring
Warm weather at any time of the year.
Most active in spring/early summer, autumn.
Management (IPM)
Best practice kits which incorporate Lucid keys
for diagnosing problems in Brassica vegetable
crops and linked to best practice management
strategies are available for commercial crops.
1. Obtain/prepare a plan that fits your situation. IPM
programs are available for caterpillars and aphids on
commercial Brassica crops. Obtain local information.
2. Crop, region. IPM management programs are
available and vary with the region and the particular
crop, eg broccoli, cauliflower cauliflower or cabbage.
3. Identification of pest must be confirmed. Consult a
diagnostic service if necessary (page xiv).
4. Monitor the crop regularly as recommended and
record results, eg
When and how often to monitor, eg weekly.
Stage of host development, eg seedling to 5 cm
head, 5-10 cm head. Number of plants inspected.
Stage of pest development, eg egg, caterpillar,
adult. Also monitor beneficial insects.
Extent of pest damage.
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? Will it be different for each variety of
Brassica and for each growth stage?
6. Action. Depends on decided threshold, especially to
seedbeds and in the field. Home gardeners usually
control caterpillars when they are first observed.
7. Evaluate IPM program to see how well it worked.
Review records of monitoring, threshold, spray
applications, release of bio-control agents, etc, for
success of treatment and future IPM improvements.
Control methods
Sanitation.
If only a few plants caterpillars can be hand
picked, but they are green and hard to find.
Remove weed hosts, keep crops weed-free.
Destroy, eg plough or dig in, infested crop plant
material to prevent development of the pest.
Biological control.
Natural controls.
– Many parasitic and
predatory insects, birds,
spiders, virus, bacterial
and fungal diseases attack
eggs, caterpillars, pupae
and butterflies, reducing
caterpillar numbers but Yellow cocoons of parasitic
not economic control. wasps on dying caterpillar.
–Some companion plants, eg dill, are reputed to
attract parasitic wasps; sage is reputed to repel the
cabbage white butterfly.
Introduced wasp parasites, eg
CWB pupal parasite (Pteromalus puparum).
CWB parasite (Cotesia glomerata).
– Apanteles glomeratus and A. rubecula parasitise
caterpillars. Their cocoons are seen on fully grown
caterpillars which stop feeding and die (see above).
.Biocontrol agents for purchase eg
–Trichogramma wasps parasitize CWB eggs.
–Dipel (Bacillus thuringiensis (Bt)) is a bacterium
which is eaten by young caterpillars feeding on
leaves. A toxin is released which kills CWB
caterpillars. It has short residual activity but is slower
acting than chemical insecticides. Caterpillars may
take several days to die so it must be applied when
caterpillars are small. It is not suitable for emergency
treatment. It is a registered pesticide and marketed
under a range of trade names (see below).
Resistant varieties.
All brassicas seem to be susceptible, but red
cabbage has fewer of the taste components
which attract adult butterflies. CWB feet carry
hairs that allow it to recognize chemicals in
the foliage on which it alights; it lays a single
egg underneath a susceptible leaf.
Overseas, some Brassicas may be bred to
produce Bt avoiding the need to spray.
Pest-tested planting material.
Ensure purchased seedlings are caterpillar-free!
Physical & mechanical methods.
In severe infestations home gardeners can place
light fine woven mesh or other material over rows
of seedlings to exclude butterflies. Seedlings grow
and lift up the mesh. Many also provide protection
from sun, light frosts and hail. Ensure adequate
light penetration and air circulation.
Screen greenhouse vents to exclude butterflies.
Insecticides.
Many insecticides are registered to control CWB
caterpillars. Thoroughly spray to penetrate
foliage and cover leaf undersurfaces.
Control caterpillars while they are small. Older
ones are less susceptible and may require
application of synthetic insecticides.
Croplife Australia Resistance strategies are
on labels and should be carefully followed.
Table 7. Cabbage white butterfly – Some insecticides and bio-control agents.
What to use?
FOLIAGE APPLICATIONS
Group 1A, eg carbaryl (not on food-producing plants in home gardens)
Group 1B, eg Orthene (acephate); Malathion (maldison)
Group 2B, eg Regent (fipronil)
Group 3A, Decis (deltamethrin); Mavrik (tau-fluvalinate);
Sum-alpha , Flex (esfenvalerate)
Group 5, eg Entrust , Success , Tracer (spinosad)
Group 6A, eg Proclaim (emectin)
Group 11, eg Dipel (Bacillus thuringiensis subsp. kurstaki),
Xentari (Bt subsp. aizawai)
Group 13, eg Secure (chlorfenapyr)
Group 21B, eg Derris Dust (rotenone)
Group 28, eg Belt (flubendiamide)
Biocontrol agents, include Groups 5 and 11 above
Others, eg garlic oil; chilli/garlic
When and how to apply?
Spinosad is derived from soil bacteria.
Bacillus thuringensis (Bt) is slow-acting.
Apply to small caterpillars.
Stomach poison, caterpillars have to eat it.
Selective, only controls leaf-eating caterpillars.
Generally several applications are required.
Insects and allied pests - Lepidoptera (butterflies, moths) 85