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).

Vegetable beetles are damaging canola

A vegetable beetle. Photo courtesy of: DPIRD.

Mark Lawrence (Farmanco) reports that vegetable beetles are causing damage to canola at the cotyledon stage at Jerramungup

Adult vegetable beetles are oval in shape and are 8mm long. They have a rounded head and flattened body. They are usually a dull grey colour, but may appear brown or almost black.

Vegetable beetles are commonly found throughout the grainbelt of WA with huge numbers seen in some paddocks with no damage to plants at all during the season. This is because their primary food preference is not plants, but rather decaying organic matter and fungi. It is likely that vegetable beetles are increasing in some crops as a result of increased stubble retention and organic matter.

These beetles have been known in some cases to cause damage to crops on warm days where the topsoil is dried out and the beetles turn their feeding towards the crop plants. In these cases, control is difficult because insecticides have little impact on them.

Lab trials conducted by DPIRD entomologist Svetlana Micic have shown that vegetable beetles will cause damage to crops if day temperatures are 20°C and above. As soon as the cold, wet winter conditions prevail ie day temperatures of 15°C and below, damage by the vegetable beetle is expected to cease.

Vegetable beetles are very tolerant of insecticides. Svetlana says that currently registered insecticides for use on false wireworm (includes vegetable beetles) on canola such as chlorpyrifos (500g a.i) at 1.0-1.5L/ha with some labels stating that the application should be incorporated into the top 50mm of soil, have suppressed damage from vegetable beetles, however, many growers and agronomists have reported these rates did not cause vegetable beetle mortality rather beetles were 'subdued' and this allowed the crops to outgrow the damage.

For insecticide information refer to DPIRD’s Autumn Winter Insecticide Guide 2020.

More information about vegetable beetles can be found at DPIRD’s Diagnosing vegetable beetle damage.

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

Article authors: Cindy Webster (DPIRD Narrogin) and Svetlana Micic (DPIRD Albany).

First field pea blackspot disease forecast for WA is available online

Field pea with blackspot. Photo courtesy of: DPIRD.

The department’s first blackspot in field peas disease forecast for Western Australia for the 2020 season is now available online.

Blackspot becomes established when spores of the fungi produced on old field pea stubble are carried into the new crop by wind after rain events. Infection may occur at any stage of plant growth.

The widespread rain that was received in summer, with the follow up showers during April, has meant that at all locations in WA maturation of the blackspot fruiting bodies on previous season’s field pea stubble has started. 

Irrespective of blackspot risk, DPIRD is encouraging growers not to sow field anywhere in WA before the week beginning 11 May for agronomic reasons. 

Esperance and Great Southern regions

Blackspot maturation on field pea stubble is quite variable across these regions.

At Boyup Brook, Gairdner, Hillman, Katanning, Kojonup, Kulin, and Newdegate maturation has only just started and the blackspot risk is still high. 

At Grass Patch, Jacup, Kondinin, Scaddan, Lake King and Pingrup the blackspot risk is already medium and will require a few more rain events to reach a low risk.

A few sites, Salmon Gums and Mt Barker, are already at a low blackspot risk.  For agronomic reasons DPIRD is asking growers not to sow field pea in the Salmon Gums area before the 11 May and much later in the season at Mt Barker.

Wheatbelt and Mid West regions

At all locations in these regions the blackspot risk is high and will need several more rain events to reduce the risk. Do not sow field peas yet in these regions.

For more information on blackspot refer to the department’s Diagnosing blackspot in field peas page.

The Blackspot Manager is a model that predicts the maturity and release of spores using weather data from the nearest weather station. Advice is given on when it is safe to sow field pea.

To subscribe to the free blackspot SMS service, text 'blackspot', your name and nearest weather station to 0475 959 932 or email Blackspot.Manager@dpird.wa.gov.au to subscribe to the direct email service.

For more information on blackspot in field peas or the forecasts contact Jean Galloway, Research scientist, Northam on +61 (0)475 959 932.

Article author: Jean Galloway (DPIRD Northam).