Cutworms

Cutworms are a sporadic pest affecting all field crops. They are readily identified by the damage they cause, as newly emerging plants are often cut off at ground level by the cutworm caterpillars, hence the name cutworm. Cutworms are widespread throughout Australia and are most damaging to winter crops during autumn and winter. Irrigated crops and pastures can be attacked any time during the year. Hosts include cereals, pulses, oilseeds and pastures.

Description

Several species of cutworms exist and they are similar in appearance. Cutworm caterpillars grow to 40 mm long, are hairless, plump and smooth with a dark head. When picked up, caterpillar cutworms curl up into a C shape. Adult cutworm moths have patterned wings, are good fliers and attracted to lights. Caterpillars and moths tend to be more active at night. Cutworm caterpillars and adults are very similar in appearance to armyworms, native budworm, lesser budworm and corn earworm. Cutworms can be distinguished by a lack of stripes, which differs to the other species.

Damage is most common when large (>20 mm) caterpillars transfer from summer weeds to autumn weeds, which usually coincides with emergence of winter crops. Entire paddocks can be decimated or severely thinned, particularly early in the season. Smaller caterpillars often feed on leaf surface tissue, producing damage similar to lucerne flea. Younger plants are more susceptible to attack than older plants.

Moths lay creamy-white eggs on plant material near the soil surface. Depending on temperature, eggs can take from three days to several weeks to hatch. Once hatched, caterpillars pass through several moults before reaching full size. Cutworms pupate in the soil and moths emerge from the pupae. Life cycle lengths vary between species and environmental conditions, ranging from one month to a year.

Control

Natural predators and fungal diseases can help reduce cutworm populations. The orange caterpillar parasite, the two-toned caterpillar parasite, the orchid dupe and some spiders all provide suppression of cutworm populations. Although cutworm numbers can be reduced by natural predators, they should not be solely relied upon for control.

Cutworm damage is worst early in the season, when summer weeds provide a food source for them to survive. Therefore, controlling summer weeds may help reduce cutworm populations and consequently minimise early season attacks.

Monitor crops either late in the afternoon or at night when cutworms are most active. Look for patchy areas or crop that has been thinned. Thresholds of two or more caterpillars per 0.5 m of row may warrant an application of registered insecticides in cereals and canola.

Cutworms are easily controlled by insecticides; if possible, apply when cutworms are active late in the afternoon or at night.

References

Bailey, P. (2007), ‘Pests of field crops and pastures: Identification and Control’, CSIRO Publishing, Melbourne, Australia

Department of Primary Industries and Regional Development (DPIRD) (2019), ‘Cutworm; pests of crop and pastures’, https://www.agric.wa.gov.au/pest-insects/cutworm-pests-crops-and-pastures

Business Queensland (2018), ‘Cutworm’, Queensland Government, https://www.business.qld.gov.au/industries/farms-fishing-forestry/agriculture/crop-growing/pests-field-crops/cutworm

Umina, P, McDonald, G and Hangartner, S (Viewed Dec 2019), ‘Cutworm’, South Australian Research and Development (SARDI), Cesar, Government of South Australia, PestNotes Southern, http://cesaraustralia.com/sustainable-agriculture/pestnotes/insect/cutworm