Cutworms

Conditions appear to have been perfect for cutworms in many regions of NSW and Victoria where large populations are causing extreme damage. While they are easily controlled, monitoring is crucial.

Where have they been reported?

There have been numerous reports of cutworm over the last ten days. (Thanks for these reports*). A canola crop west of Peak Hill in the Central West Slopes & Plains district of NSW has experienced total plant loss in about 30% of the crop, which will need to be re-sown. These damaged patches seemed to align with weeds that got away prior to sowing. The caterpillars were easily found just below the soil surface. A paddock of canola south of Temora in the Central West Slopes & Plains district of NSW has been virtually wiped out by cutworms. Almost all plants had been either nipped off or completely eaten by the larvae. The densities were moderately high (4 larvae per metre of crop). The only area not affected was the paddock border, which had been sprayed with a pyrethroid to avert mite and other pest invasions. In a second canola crop closer to Junee in the same district, cutworms had eaten out large patches of canola seedlings. The larvae in both crops were 10-30 mm in length, indicating that they were mid-stage and still to reach their most damaging potential (about 50 mm).

Further south near Lockhart in NSW’s Riverina district, cutworms in both early emerged canola and wheat were in very large numbers and 'mowing down' seedlings along the rows. Although cutworms are largely nocturnal, in this case, larvae were day-active; this is perhaps an indication of their large densities. Two clover-based dairy pastures near Deniliquin also in the Riverina district of NSW have had large areas of clover completely taken out by cutworms; the areas are growing in size (from 3-4 ha. blocks) suggesting that the larvae are spreading out. Interestingly, the damage is confined to paddocks on the western edge of a tree line, presumably because adult moths travelling on westerly winds congregated in front of the trees to lay eggs. A research entomologist has provided a general report that cutworms are active in many crops in southern NSW.

In Victoria, large numbers of cutworms have caused extensive damage to a large barley crop north of St. Arnaud in the Wimmera district. The caterpillars have chewed seedlings back to ground level, affectively wiping out almost 90% of the paddock. Cutworms have also been reported attacking a vetch crop near Donald, in the Wimmera. The larvae have completely severed plant stems just above the soil surface, causing significant damage across about 40% of the paddock. Cutworms may also be responsible for extensive damage to a canola crop near Murtoa, also in the Wimmera district. The crop, which is at the cotyledon stage, has experienced significant feeding damage typical of cutworms, with large areas of the paddock likely to require re-sowing. Cutworms are also responsible for crop damage around Elmore, in the Northern Country district of Victoria. Several canola paddocks have been affected.

Cutworm habits and behaviour

Cutworms are larvae of several species of night flying moths, most notably the bogong moth. The larvae are called cutworms because they cut down young plants as they feed on stems at or below the soil surface. They are most damaging in autumn when large caterpillars (>20 mm long) transfer from summer and autumn weeds, often as they die from knockdown herbicide, onto newly emerged seedlings. Just two or three large caterpillars can seriously damage a square metre of crop. Young plants are favoured and are more adversely affected than older plants.

Cutworms are mostly sporadic pests, causing damage, often patchy in nature, to a wide range of crops and pastures. They are mostly night-feeders and hide under the soil, soil clods or litter during the day.

Cutworms can have one or two generations per year and adults emerge in late spring/early summer, hibernate during summer, and lay eggs in early autumn. We believe that the exceptionally early autumn rains this year has provided ideal conditions for survival and rapid growth of young cutworm larvae.

Our advice

The damage caused by young larvae in a crop can remain unnoticed for some time but this can change quite quickly. Monitoring is therefore crucial particularly after small patches begin to appear. Careful inspection of the soil around damaged plants may reveal larvae, although monitoring cutworm activity is best done at night. Cutworms will continue to be a problem for growers over the next month or more.

Control options

If required, cutworms are usually easily controlled with insecticides. Reports suggest adequate control is being achieved with registered rates of organophosphates or pyrethroids. Spot spraying may provide adequate control in situations where cutworms are confined to specific regions within paddocks. Spraying in the evening is likely to be more effective as larvae are emerging to feed and insecticide degradation is minimised.

Description

There are at least three species of cutworm that cause damage to crops. Cutworm larvae are generally plump, greasy in appearance, and smooth bodied. They are usually evenly coloured, and have dark heads, dark or red-brown to pink bodies without distinct hairs and can grow up to 40-50 mm long. When larvae are disturbed they curl up into a ‘C’ and remain stiff as a defensive response. Moths vary in colour from dull brown to black with wingspans ranging from 30-50mm. Click here for images of cutworm moths.

 

* Sources of field reports of cutworms

Matthew Burkitt – Agronomist, AgriWest Rural (NSW Central West Slopes & Plains)

Matt McLoughlan – Agronomist, Mr Agronomy (Victorian Wimmera)

Rik Maatman – Agronomist, Landmark (Victorian Wimmera)

Michael Nash – Researcher, SARDI (Adelaide)

Warwick Nightingale – Agronomist, Delta Ag (NSW Riverina)

Andrew Reardon – Agronomist, JJS Glass & Co (NSW South West Slopes)

Damien Tanner – Agronomist, JSA Independent (Victorian Wimmera)

Greg Toomey – Agronomist, Landmark (Victorian Northern Country)

Matthew Tubb – Agronomist, Landmark (NSW Riverina)