More caterpillars

Pasture webworm and pasture day moth have been reported mostly in cereals

Where have they been reported?

Pasture webworm (Hednota spp.) larvae have caused patchy damage across a 250 ha wheat paddock south of Ouyen in the Victorian Mallee. Patches of damage ranged from 9-36 m², with the worst damage seen on heavier ground. Low numbers of pasture day moth (Apina Calisto) were also found in the paddock, however damage from this pest appeared to be relatively minor. Another minor population has also been reported alongside Proteuxoa in barley, north of Deniliquin in the NSW Riverina. 

We have had reports of damage by pasture day moth in tillering wheat in the Murrayville region of the Victorian Wimmera. An infestation has also been reported in capeweed growing to the side of a vetch crop on sandy ground west of Elmore in Victoria’s Northern Country. In this case the caterpillars had encroached 2 meters into the edge of the vetch crop. 

About pasture webworm and pasture day moth

Pasture webworm larvae are usually light-dark brown in colour and may have a tinge of the green gut contents showing through. They are about 1 mm long when newly hatched and reach a maximum length of about 18 mm. They have a smooth body and shiny dark heads. Older larvae have darker raised patches on each segment. Most larvae observed in the field will be large enough to be identified by the presence of these darker raised patches.

Pasture webworm damage is recognised by the presence of severed cereal plants or leaves that are spread at different angles in the crop. Sometimes leaves may protrude from silk-lined tunnels made at the base of the plants.

Pasture webworm (Source: cesar)

 

Pasture day moth (Source: cesar)

 

Pasture day moth larvae are visually striking especially when fully grown. They are dull dark brown with reddish-orange and yellow markings, and two distinctive yellow spots near the posterior end of the body. They are also noticeably hairy with prominent bristles and grow to 60 mm in length. 

Pasture day moth larvae most commonly attack broadleaved weeds in pasture, such as erodium and capeweed. In recent years, damage to emerging cereal and pasture crops, canola, peas, sub-clover and phalaris grass has been reported. This typically occurs in paddocks where pasture day moth are present and broad-leafed weeds are dead or dying from a herbicide spray; the caterpillars will transfer off the dying host plants and onto nearby crop plants.

Our advice

Spraying crops for pasture webworm is recommended when 10 plants per square metre are damaged. We recommend spot spraying when infestations are patchy. A buffer zone of 20 metres around the infestation should also be sprayed. Providing the leaves of the plant crown are green, spraying will allow quite badly affected crops to recover satisfactorily. Various synthetic pyrethroids and chlorpyrifos are registered for pasture webworm control in pastures and forage crops. Cultivation, summer fallowing and grazing can reduce the chance on damaging infestations during winter. 

The benefit of controlling pasture day moth is questionable in most years. The last substantial outbreak was in 2007 where pasture day moth were reported across much of southern NSW, mostly attacking cereals and emerging pastures.

 

Sources of field reports of pasture webworm and pasture day moth

Chris Dunn – Agronomist, Landmark (Victorian Northern Country)

Andrew McMahen – Agronomist, Landmark (Victorian Mallee)

Simon Mock – Agronomist, Clovercrest Consulting (Victorian Wimmera)

Matt Tubb – Agronomist, Landmark (NSW Riverina)