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Cutworms

Agronomist, John Jervois (Tarcutta Rural Supplies), reported that cutworms (Agrotis spp.) have caused severe damage to a several germinating triticale crops near Tarcutta, in the South West Slopes of New South Wales. The damage observed has been quite patchy, with some areas suffering 100% plant death. John said most problems were observed in paddocks that had weeds and stubble over summer, while ‘clean’ paddocks that were cropped in previous years typically had few problems. Prolonged autumn green feed is likely to have allowed caterpillars to develop to a large size by the time crops started to emerge. John says chemical control was required in the worse affected paddocks, which have now been re-sown and appear to be emerging well.

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 cutworm moths.

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.

Cutworms are often difficult to detect because they tend to feed at night and hide under the soil or litter during the day. 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.

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