Armyworms

Grower Josh Walter (Murnong Farming), reports finding significant damage to leaves and cotyledons of canola plants in a newly established crop west of Geelong, in the Western district of Victoria. No pests could be found in the affected area during the day, however upon visual inspection at night high numbers of small grubs were found feeding on the plants. Senior technical officer, Ken Henry (SARDI), has identified these as small armyworm caterpillars, which are members of the Noctuidae family. It is likely that some other unidentified caterpillars, possible loopers, were also contributing to the damage seen in this paddock.

Armyworms typically attack cereals and grass seed crops, and are most damaging when crops are close to harvest. They are not commonly known as pests of canola. Most damage generally occurs in ripening cereal crops, when armyworms chew through the last remaining green part of the plant stem, causing heads to fall to the ground. When crops are at this stage even relatively low numbers of caterpillars can cause significant losses. Assessing armyworm numbers in a crop can be difficult as they sometimes shelter on the ground beneath dead leaf material, making detection difficult. At other times they will be on the stems or heads of plants and easily found.

There are three main species of armyworms that occur in Australia: the common armyworm (Leucania convecta), the southern armyworm (Persectania ewingii) and the inland armyworm (Persectania dyscrita). All species have three parallel white stripes running from the ‘collar’ behind the head, along the body to the tail end, making them easily distinguishable from cutworms and native budworm, with which they are sometimes confused. Armyworms have large heads and smooth, fat bodies that are usually pinkish, green or brown in colour. They can grow up to 40 mm in length. Adult moths are grey-brown in colour and have a stout body with a wingspan of approximately 40 mm.