Desiantha weevil and pasture webworm larvae are active in cereal crops and pastures
Desiantha weevil larvae
- South Stirlings
- Bremer Bay
Brent Pritchard (Farmanco) reports finding desiantha weevil larvae in wheat and barley crops in the South Stirlings area. Damage has been patchy with dead plants being yellowed, but on close inspection roots have been cropped and larvae were in close proximity.
A grower at Bremer Bay also reports finding desiantha weevil larvae in a late sown barley crop that is at early tillering. Damage is patchy but there are 3-5 desiantha larvae in the vicinity of dying cereal plants. The damage is worse adjacent to the crop edge with an estimated damage of 20% of the crop in this area.
The larvae of desiantha weevils, are white legless creatures that grow to 6 mm long with orange/brown heads. They remain under the soil and are difficult to find if in low numbers. They feed on the underground parts of seedlings and can cause a reduction in plant growth, wilting and eventual death of plants.
Desiantha weevil larvae feed underground on germinating seeds or stems often killing plants or causing abnormal or stunted growth. Desiantha weevil larvae are white, legless, with orange-brown heads and up to 6mm long. Larvae remain under the soil and are difficult to locate, although some painstaking digging may reveal larvae close to plants.
Adults (also known as spotted vegetable weevil) are mottled grey-black weevils about 5mm long with the typical weevil snout.
Desiantha weevils are usually found hiding under stubble and under plant residue during the day. This can protect the weevils from coming into contact with insecticides, making them difficult to control.
Effective control of grass weeds in previous season and of green bridge following summer rain will minimise the risk of crop losses from desiantha. The only in-crop treatment is to re-sow with seed treated (in severe cases) with chlorpyrifos, which is registered for desiantha weevil control in cereals.
For more information on desiantha weevils visit DPIRD's Diagnosing Desiantha weevil in cereals.
Pasture webworm
- Bremer Bay
Brent Pritchard (Farmanco) reports pasture webworm larvae killing established grass pasture in Bremer Bay. They have caused over 20% damage and were active during the day.
Pasture webworm larvae are brown caterpillars with black heads that feed nocturnally and hide by day in silk lined tunnels nearby freshly chewed plants. They can grow up to 15mm in length.
Pasture webworm prefer to feed on grasses and cereal plants, and so germinating cereal crops should be monitored especially where a pre-sowing or post sowing pre-emergent insecticide was not applied. Pasture webworm can completely destroy sections of crop.
Pasture webworm are readily controlled with insecticides.
More information on pasture webworm can be found at DPIRD’s Diagnosing webworm page.
Growers and consultants can use the PestFax Reporter app to submit photos, request identification and report caterpillar activity in crops and pastures.
They can also refer to GRDC’s recently updated Insects of Southern Australian Broadacre Farming Systems Identification Manual and Education Resource 2nd Edition.
For insecticide recommendations refer to the department’s 2019 Winter/spring insecticide guide.
For more insect information contact:
Svetlana Micic, Research Officer, Albany
+61 (0)8 9892 8591
Dustin Severtson, Development Officer, Northam
+61 (0)8 9690 2160
Alan Lord, Technical Officer, South Perth
+61 (0)8 9368 3758
Article author: Cindy Webster (DPIRD Narrogin) and Svetlana Micic (DPIRD Albany).