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Cutworms

Agronomist, Glenn Sheppard (IMAG Consulting), reports cutworms (Agrotis spp.) damaging a wheat crop near Dubbo, in the Central West Slopes and Plains district of New South Wales.  Glen says the larvae are approximately 15-20 mm long and quite abundant, with 2-3 caterpillars observed per square metre. Glen reports chewing damage and ring barking to the above ground stem area with some plants eaten completely through, leaving only the stumps.

Jon Shuter (NSW TAFE) has also reported cutworm damage to several recently sown pastures near Wagga Wagga, in the South West Slopes of New South Wales. Jon says the damage is patchy, and does not warrant control at this stage.

There are at least three species of cutworm that cause damage to crops. Cutworm larvae are generally plump, greasy in appearance, and smooth bodied with most having uniform colouring ranging from pinkish brown to black. They grow up to 40-50 mm long and hide under the soil or litter by day, making them difficult to detect. They can often be located by scratching the surface near damaged plants; when disturbed they 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.

Cutworms can have several generations per year and adults emerge in late spring/early summer. The larvae are sporadic pests, causing damage (often patchy) in a wide range of crops and pastures. 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.

Because cutworms are usually hard to find, numbers can often be underestimated. Monitoring is best achieved at night when larvae come out to feed. Cutworms are easily controlled by insecticides. Spraying in the evening is likely to be more effective as larvae are emerging to feed and insecticide degradation is minimised.

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