Diagnosing webworm
Webworm larvae are leaf-chewing pests of seedling wheat and barley.
What to look for
- Bare patches in emerging crops.
Paddock
- Oldest leaves have been removed or are severed at ground level.
- Leaves are scattered on the ground or pulled into web-lined holes near the plants.
Plant
- Small tan coloured moths with wings that fold closely around the body in a nearly vertical position, enabling the moth to blend with its surroundings.
Insect Adult
- Brown caterpillars up to 15mm long with black heads, which hide in web-lined tunnels during day.
- Larvae tend to be more common on of edge of patches.
Insect Larvae
What else could it be
| Condition | Similarities | Differences |
|---|---|---|
| Diagnosing cutworm in cereals | Removal of leaves | Cutworms do not drag severed leaves down tunnels. |
Where did it come from?
- Caterpillars hatch from eggs laid amongst grass in autumn and feed throughout the winter.
- Spring and summer are passed in the tunnels as resting stage caterpillars. After this, they pupate and emerge as adult moths, which are about 10mm long and may be seen flying in large numbers on autumn nights.
Management strategies
Spraying insecticide
- If 25% of plants are being seriously damaged at or just after emergence, spraying should not be delayed as continued feeding will kill many plants and result in bare ground or thin areas.
- Webworm eggs will not be laid in large numbers or survive well in a bare paddock or in stubble.
- Three week fallow at the break of the season will starve any caterpillars present.
How can it be monitored?
- Check emerging crops seeded into areas where fine, dry grasses were prevalent during autumn for signs of damage. Careful digging at the base of recently-damaged plants may reveal web-lined tubes with caterpillars inside, or a search at night may reveal feeding activity.
Page last updated: Monday, 1 May 2017 - 12:09pm