Armyworms

Agronomist, Matt Witney (Dodgshun Medlin), has reported finding armyworms in several barely and wheat crops near Sea Lake, in the Mallee district of Victoria. The caterpillars were found in very high numbers across several crops and Matt estimates that 10-20% of plant stems have been chewed off in the worst affected paddocks. The caterpillars are about 30-40 mm long and they have completely severed stems anywhere from the ground level to half way up the plants. In some paddocks the infestations have warranted chemical control and Matt says alpha-cypermethrin has worked well.

Armyworms attack cereals and grass seed crops, and are most damaging when crops are close to harvest. As plants mature, armyworm caterpillars chew through the remaining green part of the plant stem, causing heads to fall to the ground. Crops at this stage, particularly barley, should be closely monitored as 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. The first sign of armyworms is often the presence of dried frass (droppings) about the size of a match head at the base of plants.

The 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 which 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.