Pasture webworm

Consultant, Andrew Newall (NEWAG Consulting), has reported pasture webworm (Hednota spp.) attacking early tillering wheat just west of St. Arnaud, in the Wimmera district of Victoria. It is likely the webworm were present in the affected paddock last year, which was sown to pasture. Andrew reports that the caterpillars had chewed through wheat plants at the ground level, causing enough damage to warrant chemical control. Pasture webworm caterpillars have also been identified for consultant, Peter Lott (Rural Management Strategies). The caterpillars were observed attacking a canola crop near Temora, in the South West Slopes of New South Wales.

There are several species of pasture webworm and they can be difficult to distinguish. The larvae are usually light-dark brown in colour, growing to about 18 mm long. They have a smooth body and shiny dark heads. Pasture webworm feed at night and hide in web-lined tunnels beneath the ground by day. They typically feed on the soil surface or pull plant material into their tunnels.

Pasture webworms are relatively insignificant pests of pastures, but can cause large losses to establishing cereals. The caterpillars commonly attack establishing crops of wheat, barley and rye. Damage almost invariably results from a rotation of cereals following a pasture phase. They have not previously been recorded causing damage to canola plants. 

The adults are long-legged moths with the enlarged mouthparts arranged in a beak-like projection. They are 10-12 mm long with a wingspan of about 22 mm. Moths are easily detected. They fly up from pastures in the autumn; this serves as a warning of the risk of damage later that year.

Monitor crops that have been seeded into areas that were pasture last year or where stubble and grasses were prevalent in autumn. Digging at the base of recently damaged plants may reveal web-lined tunnels and caterpillars inside or a search at night may reveal feeding activity. Pasture webworms are easily confused with the pasture tunnel moth.

Click here for images of pasture webworm.