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Armyworms (Family: Noctuidae) are often problematic to cereal crops and grasses at this time of year, and growers are encouraged to keep an eye out for their activity. Armyworms can be quite damaging when crops are approaching harvest. This is because they climb up plants and chew through the last remaining green part of the plant stems (just below the head), causing the heads to fall. Ripening barley is most susceptible to armyworm damage. At this time of the year, even relatively low numbers of caterpillars can cause significant yield losses. Armyworms will also attack wheat, oats, triticale and pasture, but these crops are less susceptible than barely.

Armyworms can be difficult to detect as they sometimes shelter on the ground beneath dead leaf material, particularly during the day. At other times they can be easily found on the stems or heads of plants. The first visible sign of armyworm caterpillars is often their straw to green coloured droppings (frass), about the size of a match head, found on the ground between cereal rows. Treatment (if warranted) should be carried out in the late afternoon or early evening, as many species are nocturnal feeders.

Armyworms owe their name to the observation that caterpillars sometimes ‘march’ in large numbers away from areas within a paddock that are crowded and depleted of food. Armyworm caterpillars grow up to 40 mm in length and usually have smooth bodies with fine hairs. Body colour can vary, but caterpillars are generally green, brown or yellow with three parallel white longitudinal stripes running from the 'collar' behind the head, along the body to the tail end.

For further information on armyworms click here, and for images click here.

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