Armyworm cause most damage in cereal crops close to harvest
- Nangetty
- Mooriary
- Arrino
An armyworm caterpillar. Photo courtesy of: DPIRD.
Rachel Mason (Mingenew Irwin Group) has recently found armyworm (ranging from one to seven caterpillars per five sweeps) when sweep netting wheat crops at Nangetty, Mooriary and Arrino.
Armyworm caterpillars are fat and smooth and may be distinguished by the three parallel white stripes on the collar just behind the head.
Growers need to be mindful of correctly distinguishing armyworm caterpillars from the recently introduced fall armyworm caterpillar and from native budworm caterpillars.
Armyworm caterpillars are most damaging in barley crops close to harvest so monitor crops now. When barley crops are maturing in spring, large armyworm caterpillars climb plants and can chew through the stems, causing the heads to fall to the ground. Damage to wheat and oat crops occurs less frequently and is usually minor compared to damage in barley because the stems are thicker and leaf defoliation does not usually result in yield loss. Armyworms are seldom a serious problem in pastures.
The economic level for spraying armyworm in mature barley is about three large armyworm grubs per square metre of crop. The threshold for wheat or oats is much higher as only grains are consumed and heads are very rarely dropped. Spray thresholds in these crops are more like 10 grubs per square metre of crop. If applying insecticide be mindful of harvest chemical withholding periods (WHP) and to check chemical labels before spraying.
A number of effective insecticides are registered for the control of armyworm if required (see DPIRD’s 2021 Winter Spring Insecticide Guide).
To read about previous armyworm activity reported to PestFax this season refer to the 2021 PestFax Issue 16 article Caterpillars in cereal crops: armyworm or budworm? and 2021 PestFax Issue 14 article Armyworm.
For further information on armyworm, refer to DPIRD’s Diagnosing armyworm and Management of armyworm in cereal crops pages.
For more information, contact Technical Officer Alan Lord, South Perth on +61 (0)8 9368 3758 or Research Scientist Svetlana Micic, Albany on +61 (0)8 9892 8591.
Article authors: Cindy Webster (DPIRD Narrogin) and Dustin Severtson (DPIRD Northam).