Corn earworm and native budworm
These two species can be difficult to distinquish. The colour of the larvae in both species can vary widely. However, an important management difference is that the corn earworm (H. armigera) has a greater capacity to develop resistance to chemical pesticides. For this reason, careful management is essential.
Helicoverpa armigera (corn earworm) and Helicoverpa punctigera (native budworm)
|Description of adult|
The adult moths of the native budworm (Helicoverpa punctigera) are very similar to those of the corn earworm (Helicoverpa armigera), but differ in two major characteristics. While newly emerged corn earworm moths have a distinct kidney-shaped spot in the middle of the forewing, this is diffuse in the native budworm. The dark bands on the hind wings are also distinctive. The corn earworm has a pale patch in the middle of this band towards the edge of the wing, whereas the native budworm does not. Adults fly mainly at night and are strongly attracted to light.
The pearly white, ribbed eggs, about half the size of a pinhead, are laid singly. The larvae vary in colour from pale to dark green, and markings that are prominent on the back of corn earworm larvae are usually faint or absent in the native budworm. They can grow to 40 mm in length. The larvae are smooth skinned and sparsely covered with stiff hairs that can be readily seen if the caterpillars are held up to the light. The reddish-brown pupa is formed at the end of a burrow in a soil cell 5-10 cm deep.
The life cycle is similar in both species. The eggs hatch in three to seven days in warm weather. Larvae are mature after two to three weeks and pupate in the soil. Adults emerge after a further two weeks. The life cycle takes about five to seven weeks in summer. Subsequent generations survive on successive plantings of a crop or on a succession of different crop hosts. Pupae pass the winter in a resting state (diapause) and emerge as adults either from September to October or in late summer.
H. armigera is a pest of monocotyledons (grasses and sedges) and dicotyledons (broad leafed plants). H. punctigera occurs only on dicotyledons.
Crop hosts include cotton; grain sorghum; maize (corn); millet; sunflowers; winter cereals, such as wheat, oats, barley and triticale; linseed; pulses; pasture legume seed crops, such as chickpeas, cowpeas, mungbeans, pigeon pea and soybeans; and horticultural crops, such as cherries, cape gooseberries, french bean, pepino tomatoes and citrus. Canola, safflower and ornamentals are also attacked. Weed hosts include noogoora burr, common sowthistle, fat hen and marshmallow. In other words, helicoverpa caterpillars, and in particular H. armigera, are not fussy about what they eat.
Major and frequent. The larvae cause damage to flowers and bore into fruit. Often, large entry holes in the fruit are evident and extensive internal rotting can occur.
Shake the plants onto a white sheet or cut-open fertiliser bag. Examine five 1 m sections of row at six widely spaced locations throughout the crop. Examine the crop twice weekly from early flowering until crop maturity.
Biological A number of egg and larval parasites occur but seldom provide sufficient control. Other biological sprays are also available for use against helicoverpa.
Chemical registrations and permits