PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Cabbage white butterfly
An example of a leafeating caterpillar
Scientific name
The introduced cabbage white butterfly (Pieris
rapae, Order Lepidoptera) is the most serious
economic butterfly pest in Australia. Its status as a
pest varies depending on the crop and the region.
Host range
Butterflies visit a wide range of flowers to feed on
nectar. Caterpillars feed on Brassicas (crucifers)
and some other species.
Ornamentals, eg stock, wallflower, geranium,
mignonette, nasturtium, spider flower (Cleome).
Vegetables, eg broccoli, cabbage, cauliflower,
Brussel sprouts, radish, mustard, kale and turnip.
Field crops, eg canola, rape.
Weeds, eg shepherd's purse, wild mustard.
Description & damage
Butterflies, although popularly referred to as
‘white’ butterflies, are usually a general gray-white
and have a wingspan of 40-50 mm. Hindwings
beneath are yellow and the forewings are paler.
Females have 2 black spots on the upper surface of
each forewing, while males have only one spot.
Both sexes have one black spot on each hindwing.
Larvae (caterpillars) are velvety green, covered
with fine short hairs 20-30 mm long when fully
grown with a faint yellow stripe down the back and
along each side. They are well camouflaged, their
color closely resembles that of the plant on which
they are feeding. Caterpillars generally feed at
night and frequently rest during the day with their
bodies extended along leaf midribs and are not
readily seen. Tell-tale droppings often reveal the
location of caterpillars. Pupae are about 18 mm
long, light gray, yellow or green and are attached
to the host plant or some nearby object.
Leaves/heads. Young caterpillars feed
mainly on leaf undersurfaces while older
caterpillars feed from the uppersurfaces and eat
large irregular holes from the outer leaves of
broccoli or cauliflowers. Greenish-brown pellets of
excrement are caught in the angles of leaves. Only
leaf ribs and veins of seedling leaves may be left.
General. So much of the leaf tissue is generally
eaten by these caterpillars that the growth of plants
is seriously interfered with and the heads of
cabbages or cauliflowers are stunted or do not form
at all. Leafy vegetables are rendered unfit for
human consumption.
Diagnostics. Do not confuse damage with
that caused by:
Other caterpillars seen on the plant or on the
ground which attack brassicas, eg cabbage moth,
cluster caterpillar, diamondback moth, etc. Some
are more damaging than others. Different species
vary greatly in size. Keys assist identification of
caterpillar pests of brassicas.
Snails and slugs which chew holes, leave snail
droppings and slimy glistening trails.
Bird damage, eg silver eyes, which feed on
seedlings.
Over-mature cabbages which split overnight.
Caterpillar droppings of various species can be
found under infested plants.
If still unsure seek advice.
Pest cycle
There is a complete metamorphosis (egg,
larva, pupa and adult), with at least 2 generations
each season. Females lay pale yellow eggs singly,
usually on the undersides of the outer leaves,
which provide food for young caterpillars. When
fully grown they pupate on the food-plant, some
nearby object, or even on debris on the ground.
The pupa is attached by its tail to a silken pad; its
body is supported by a fine silken girdle around the
middle. Females may live for up to 4 weeks
during which time they lay several hundred eggs.
Fig. 56. Cabbage white
butterfly (Pieris rapae).
PhotoNSW Dept of Industry and
Investment (E.H.Zeck). `
1. Egg (x10)
2. Larva or caterpillar (x2.5)
3. Pupa or chrysalis (x 2.5)
Actual size
4. Eggs on leaf
5. Larva or caterpillar
6. Pupae attached to plant
7. Adult butterfly
84 Insects and allied pests - Lepidoptera (butterflies, moths)