Farmers are urged to closely monitor cereal crops and grass-based pastures for armyworm, with Victorian grain growers increasingly reporting the pest at damaging levels.
Agriculture Victoria Land Management Extension Officer Heather Drendel said armyworm can be distinguished from other caterpillar pests by three pale stripes located behind the head, which sometimes run the length of the body.
If monitoring in the daytime, growers should get down to soil level and dig around the base of plants to look for caterpillars and symptoms of crop damage.
Faecal pellets around the base of plants are another indication of an armyworm infestation. A sweep net is not as useful in the daytime, so some growers opt to monitor at night as armyworm is nocturnal. When ground sampling, it is necessary to do at least 10 spot checks in the crop.
The earlier the detection, the less the damage. The most serious armyworm damage in cereal crops occurs when larvae feed on the upper flag leaf and stem node as the crop matures. Larvae target the node as the leaves become dry and unpalatable, and the stem is often the last part of the plant to dry.
Ms Drendel said growers in the Wimmera have reported a need to control armyworm in their cereal crops as they reached damaging levels.
“There are higher numbers than usual this year in some crops. However, it is quite sporadic, so we are urging growers to monitor paddocks closely,” she said.
Growers should only spray armyworm when the thresholds are met, which vary with the growth stage of the crop. Spraying can also kill beneficial insect species, so it should only be undertaken if required. Young larvae, up to eight millimetres, cause very little damage and are more difficult to find.
Julia Severi, Extension Scientist with cesar, said when numbers are high, armyworm can do a lot of damage by chewing foliage. Later in the season when crops are ripening, large armyworm populations can lop cereal heads. In that case, the spray threshold is about one to three caterpillars per square metre.
“Armyworm is highly migratory. In south-eastern Australia, there are three different species that can occur throughout the winter-cropping season and are difficult to distinguish reliably in the caterpillar form. Armyworm can be found at all times of the year, unlike native budworm,” she said.
Source: Agriculture Victoria