Other similar species armyworm can be confused with
Cutworms are also smooth caterpillars but are usually only pests of cereals at the seedling stage and appear at a different time of the year. They do not climb and sever heads from the stems.
Another caterpillar, Helicoverpa puntifera, which is a closely related species to the native budworm, feeds only on individual grains and is not usually as damaging in barley as the armyworm.
Helicoverpa puntifera may be recognised by its rough skin sparsely covered with bumps and bristles.
Lifecycle of armyworm
The speed of development depends on temperature. In winter it may take several months for eggs to develop into moths. A generation may be completed in six weeks in warmer weather when crops are maturing.
Occasionally, armyworm moths move in large flights in search of food, but usually a damaging population will have bred within the paddock or local area. Caterpillars which have bred in high densities may be almost black, compared with the usual lighter shades.
Assessing the numbers of armyworm in a cereal crop can be difficult, as their movements will vary with weather conditions and feeding preference. Sometimes they are found sheltering on the ground and under leaf litter, whilst on other days they will be high up on the plants or on the heads and easily picked up using sweepnets.
If ryegrass is present in the crop, they often prefer to feed on that, until it runs out.
Armyworm caterpillars may be confined to only small portions of a crop. Several different locations within the crop should be checked for caterpillar numbers before deciding on control measures.
A suggested monitoring procedure is:
- Look for signs of caterpillar droppings and damaged ryegrass heads (if present).
- Look for damage to the foliage of the crop.
- Look for caterpillars on the plants and on the ground after shaking the plants and searching the leaf litter between rows.
- If caterpillars are present, check frequently for the first signs of head-lopping in barley.
If you can't find caterpillars in spring, it can be two or three weeks before a population of damaging-sized caterpillars could develop, so check again in at least two weeks time.