PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Corn earworm
Cotton bollworm, tomato grub, tobacco budworm
Scientific name
Corn earworm (Helicoverpa armigera, Family
Noctuidae, Order Lepidoptera) is said to be the
world’s worst agricultural pest. It is a major pest
in NSW, Vic and WA and costs Australian growers
more than $200 million each year. Related pests
include:
Native budworm (H. punctigera)
Cape gooseberry budworm (H. assulta)
Indian weed caterpillar (Heliothis rubrescens)
Host range
Many different commercial crops, eg
Ornamentals, eg calendula, carnation, dahlia,
everlasting, hollyhock, snapdragon.
Vegetables, eg bean, pea, sweetcorn, tomato.
Fruit, eg young apple, peach, strawberries.
Field crops, eg clover, cotton, linseed, maize,
soybean, sunflower, pasture, grasses, winter cereals.
Weeds, eg capeweed, deadly nightshade, fat hen,
Scotch thistle, stinging nettle.
Description & damage
Moths (adults) are stout, brownish, with a
wingspan of about 40 mm. There are distinctive
dark markings on fore and hindwings. Moths hide
among foliage during the day and fly at dusk, feed
on nectar and lay eggs on young growth. Eggs
are easily seen as they are about 0.5 mm in
diameter, dome-shaped, flattened at the base and
ribbed. They are initially whitish but change to
brownish shortly before hatching when the head
and body of the caterpillar can be seen.
Caterpillars (larvae, bollworms, budworms,
earworms) grow to 40-50 mm. Initially pale green
or cream they change to shades of green, fawn,
yellow, or red-brown depending on the foliage on
which they are feeding. Brown or black stripes run
along the body. Small larvae have bristle-like hairs,
large caterpillars are smooth. There is no webbing.
Pupae are brown, about 2 cm long and are
found in soil.
Damage.
Young caterpillars feed on young leaves
but soon move to buds, flowers, young fruit or
seeds and eat their way in.
Older larvae burrow into flower buds and
fruit. Caterpillars may wander from fruit to fruit.
Entry holes of tiny caterpillars are easily overlooked
but as the caterpillars grow, entry holes
are bigger and more easily seen (Fig. 57).
Damage may continue postharvest.
In the laboratory caterpillars can eat through
plastic.
Diagnostics. Holes in buds and flower heads
indicate infestation. Caterpillars are distinctive.
State fact sheets assist with identification.
It may be necessary to seek specialized help to
distinguish corn earworm from native budworm
and other caterpillars (page xiv).
To confirm that H. armigera is present and not
H. punctigera (which is easily controlled with
insecticides), CSIRO has developed a test which
involves squashing eggs and larvae on to
Lepton TM membranes, a particular colour change
indicates H. armigera. Mainly used by
diagnostic services.
Scientists are sequencing the moth’s genome
(unraveling its 14,000 genes) which they think
will discover its weaknesses, and the
development of specially designed insecticides.
Fig. 57. Corn earworm, cotton bollworm, tomato
grub (Helicoverpa spp.). Upper: Caterpillars (about 40 mm
long) boring into sweetcorn cobs; Lower: Caterpillars boring
into tomato fruit. PhotoCIT, Canberra (P.W.Unger).
Fig. 58. Corn earworm life cycle.
86 Insects and allied pests - Lepidoptera (butterflies, moths)