Cutworms

Cutworms (Agrotis spp.) have been identified for agronomist, Roger Garnsey (Roger Garnsey Agronomy), who observed the caterpillars in a forage brassica crop near Yass, in the Southern Tablelands district of New South Wales. The crop was sown in late winter and already approximately 25 ha has been completely defoliated. In the affected areas, cotyledons have been chewed off and only the stalks remain, which is typical of cutworm feeding damage. The paddock was sown to pasture last year and Roger says a high amount of cape weed was present. Agronomist, Matt Witney (Dodgshun Medlin), has also reported finding high numbers of cutworms in a wheatcrop south of Ouyen, in the Mallee district of Victoria.

There are several species of cutworm that attack field crops. The caterpillars are hairless, generally plump, greasy in appearance and smooth bodied. Most species have uniform colouring, ranging from pinkish brown to black. They grow to 40-50 mm long and when disturbed curl up and remain stiff as a defensive response. Moths vary in colour from dull brown to black, with wingspans ranging from 30-50 mm.

Click here for images of cutworms.

Cutworms can have several generations per year and adults emerge in late spring/early summer. The larvae are sporadic pests, causing damage (often patchy) to a wide range of crops and pastures. Just two or three large caterpillars can seriously damage a square metre of crop. They are most damaging in autumn when large caterpillars (>20 mm long) transfer from summer and autumn weeds onto newly emerged seedlings. Young plants are favoured and are more adversely affected than older plants.

Despite the significant amount of damage, Roger says only a few cutworms could be found upon visual inspection. This is probably because cutworms prefer to feed at night and tend to hide under the soil or litter during the day, making detection difficult. Monitoring is best achieved at night and if required cutworms are usually easily controlled with insecticides. Spraying in the evening is likely to be more effective as larvae are emerging to feed and insecticide degradation is minimized.