PestFacts WA

Caterpillars continue to cause concern

Weed web moth and cabbage centre grubs

• Beverley
• Quairading
• Kweda
• Highbury
• Bruce Rock
• Wagin

Cabbage centre grub caterpillar on canola. Photo courtesy of: Salzar Rahman (DPIRD).

Technical Officer Salzar Rahman (DPIRD) has found cabbage centre grubs (Hellula sp.) causing damage to his canola trial near Beverley.

Cabbage centre grub on roadside wild radish. Photo courtesy of: Amber Balfour-Cunningham (DPIRD).

Technical Officer Amber Balfour-Cunningham (DPIRD) recently found cabbage centre grub caterpillars on roadside wild radish near Quairading and Kweda while conducting green bridge surveillance.

Research Scientist Christiaan Valentine (DPIRD) has found small cabbage centre grubs (8-15mm long) in wild radish and roadside canola near Highbury, Bruce Rock and east of Wagin whilst surveying for diamondback moth larvae. This indicates that the moths, which are a pest of broadleaved plants such as canola, have been flying in the area and laying eggs on available plants.

Weed web moth and cabbage centre grubs are in the same family (Crambidae) and can look very similar, especially the brown banding down the body of caterpillars. They also both produce webbing amongst the leaf tissue. The most distinguishing characteristic of weed web moth is the dark circles or spots along the body (see image below).

Weed web moth caterpillars can be distinguished from cabbage centre grub caterpillars by the presence of dark circles along their body. Photos courtesy of: DPIRD. 

For more information about these pests refer to cesar’s recent PestFacts south-eastern newsletter articles Cabbage centre grubs in establishing canola and forage brassicas and High numbers of web-spinning moth larvae are feeding on broadleaf plants.

Brown pasture looper

• Williams

Brown pasture looper caterpillar. Photo courtesy of: DPIRD.

Hilary Wittwer (Planfarm) has found a number of caterpillar species in a paddock near Williams which was sprayed out with herbicide to control weeds. One unknown type was black and hairy and unlikely to be a crop pest, while another was the brown pasture looper, a known pest of broadleaved crops such as canola and pulses.

Brown pasture looper caterpillars are slender, grey or brown in colour with black and cream stripes and they move with a characteristic looping motion.

Brown pasture loopers have one generation per year and are likely to starve to death within two weeks if no host plants are available. For more information see DPIRD's Diagnosing brown pasture looper page.

Managing caterpillar pests

If you are considering chemical control for caterpillar pests refer to DPIRD’s 2020 Autumn winter insecticide spray guide.

The PestFax team wants to know what invertebrate insects you are finding in your crops and pastures, whether it is a pest, beneficial or unknown. We even want reports of the usual insects that are seen every season. Please send your reports or identification requests in via the PestFax Reporter app.

For more information on monitoring insects in emerging crops refer to;

• DPIRD’s Monitoring insects and other crop pests page
• GRDC’s Monitoring for insects in canola. Part 1 video
• GRDC’s updated I SPY manual.

For more information contact research scientists Dustin Severtson, Northam on +61 (0)427 196 656 or Svetlana Micic, Albany on +61 (0)427 772 051.

Article author: Dusty Severtson (DPIRD Northam) and Cindy Webster (DPIRD Narrogin).