Caterpillar pests

Along with cutworms, many other caterpillar pests appear to be ‘enjoying’ the mild conditions of this year. Although little is known about many of the species, being able to distinguish the pest (and its feeding damage) is a critical first step in successful management.

 

Armyworms

Faba bean crops near Boomi, in the NSW North West Slopes & Plains, have been under attack from armyworms, probably the beet or lesser armyworm (Spodoptera exigua). The crop was about 15-25 cm in height and had experienced patchy feeding damage. In the past few weeks, the problem has subsided without insecticide use, possibly due to the effects of beneficial insects or virus.

The beet armyworm is a sub-tropical species that only attacks broad-leaf plants. On hatching, clusters of young caterpillars feed by initially scraping the surface of the leaf. Later instars move on to other leaves and feed voraciously, producing large irregular holes. From this point, these armyworms can quickly skeletonise leaves as they attack in clusters. High infestations can cause severe defoliation. The larvae of beet armyworms undergo several colour phases from green to almost black.

Armyworm-like caterpillars

In the Victorian Wimmera, several caterpillar species have been climbing barley plants and defoliating flag leaves in cereal crops near Nhill. Some of these caterpillars were armyworm-like (with 3 prominent white stripes behind the head on the cervical collar), but belonged to quite different genera, possibly Ectopatria or Diarsia. Almost nothing is known about the lifecycle or management of either group of caterpillars. The caterpillars were observed feeding during the day, and in one paddock, leaf damage was reasonably consistent across the paddock.

Pasture tunnel moths

In Victoria’s South West, pasture tunnel moth (Philobota productella) larvae have damaged pastures and crops near Cavendish (ryegrass seed crop) and south of Hamilton (new phalaris clover pasture). In the first crop, there were high densities of about 15-20 tunnels per square metre and the ryegrass was severed at the base. Omethoate applied for earth mite control had no effect on the caterpillar survival.

Pasture tunnel moths are native to Australia. They are normally found in higher rainfall districts and can cause significant damage to annual and perennial grasses, clovers and occasionally crops. When the insects occur in high densities, patches of establishing cereal crops or pastures may be eaten bare. Damage is usually not noticed until early winter, with the worst period being from July until September. The larvae cease to feed in October and then close the entrances to their tunnels.

Pasture tunnel moth larvae are slender (about 2-3 mm wide) and grow up to 35 mm long. Larvae construct silk-lined tunnels that protrude above the soil surface forming a “chimney”. Larvae leave their burrows at night and feed on nearby plants. Adult moths are elongate, 20 mm long, creamy-white in colour and have a wingspan of approximately 25 mm and glisten like satin in the sun. Paddocks should be inspected now and throughout winter for signs of damage and formation of their ‘chimneys’ or silk-lined burrows.

Anthelid caterpillars

Caterpillars of a distinctively hairy appearance have damaged a young canola crop, south of Forbes in the NSW Central West. The caterpillars have caused leaf scalloping, and in some cases, defoliated the plant right back to the stem. The paddock, which was previously fallowed, contained relatively few broadleaved weeds and grasses prior to sowing this season. Most caterpillars were about 20 mm in length with a dark maroon head and legs, and a black abdomen. They were covered in numerous black, long hairs or bristles. Very little is known about this pest; the larvae belong to the Anthelid group (Pterolocera spp.) but are different to the grass anthelid, a minor pest of cereals and pasture grasses. We have not previously received reports of anthelid caterpillars attacking canola.

Pasture day moth caterpillars

Pasture day moth caterpillars have been attacking wheat (pre-tillering) north of Donald in the Victorian Wimmera. High numbers of this distinctively marked caterpillar have been causing significant damage by feeding on the new leaves of pre-tillering plants. Pasture day moth caterpillars have a preference to feed on broad-leaved weeds and will often leave canola, cereals and grasses untouched where they have a choice. However, in paddocks where broad-leaved weeds are dying from a previous herbicide spray, the grubs will transfer off the dying host plants and onto nearby plants. Refer to PestFacts Issue No. 4 for further information on the pasture day moth (Apina callisto).

Our advice

Although cutworm damage is evident through much of the cropping area of NSW and Victoria, we recommend that particular care is taken to monitor and accurately identify the cause of ongoing crop damage. The impact of cutworms will diminish as crops become established, but there are many other species of caterpillars that will continue to defoliate crop plants. Cutworms are unlikely to be associated with extensive foliage damage.

 

* Sources of field reports of caterpillars

Mathew Burkitt – Senior Agronomist, AgriWest (NSW Central West Slopes & Plains)

Rik Maatman – Agronomist, Landmark (Victorian Wimmera)

Adam Pearce – Agronomist, Clovercrest Consulting (Victorian Wimmera)

Chris Teague – Agronomist, Landmark (NSW Northern Slopes & Plains)

Georgie Rees – Agronomist, Elders (South West Victoria)