PestFacts WA

Diamondback moth numbers have increased at Esperance

• Cunderdin
• Dalwallinu
• Condingup
• Gibson
• Mount Ridley

Diamondback moth caterpillar. Photo courtesy of: Dusty Severtson (DPIRD)

An agronomist has reported sweep netting more than 100 diamondback moth (DBM) caterpillars per 10 sweeps in an early flowering canola crop near Cunderdin. This was in a paddock hotspot but low numbers of DBM were in surrounding canola crops in the area.  A control spray will be applied to the paddock.

Claire Johnston (Elders) reports that generally low numbers of DBM caterpillars are being found in canola crops in Dalwallinu and surrounding areas. With warmer spring weather, it is anticipated that numbers will increase in coming weeks.

Diamondback moths captured in surveillance traps from 17 August to 31 August 2020. Map courtesy of: Amber Balfour-Cunningham (DPIRD).

A DBM surveillance project funded by GRDC, led by DPIRD, is using DBM pheromone traps to predict where DBM are in the landscape (see map above). Each trap is located within a canola crop. Traps located in the Esperance area are capturing higher numbers of DBM than traps located elsewhere. Indicating that canola crops in the Esperance region should be monitored for DBM caterpillars.

Rob Hughes (SEAR) has found 216 DBM moths on his sticky trap and an average of 8 DBM caterpillars in 10 sweeps in the adjacent canola crop at a site near East Condingup.

Technical Officer Joel Kidd (DPIRD) found 60-160 DBM moths on sticky traps at three sites around Gibson. In the adjacent canola crops, DBM caterpillars were in low numbers, well below thresholds.

If you are sweep netting canola crops for DBM caterpillars please use the PestFax Reporter app to report and share your findings. It will help the DBM surveillance project team to determine how well the pheromone traps have worked in predicting where DBM are.

Managing DBM later in the season

DBM thresholds for control are:

•           Early to mid-flowering (no stress) - 50 caterpillars or more per 10 sweeps

•           Mid to late flowering (no stress) - 100 or more caterpillars per 10 sweeps

•           Pod maturation - 200 or more caterpillars per 10 sweeps.

Moisture stressed crops are more susceptible to insect damage, so a lower threshold may be used if extended dry periods are experienced.

DBM have less impact on yield once canola crops stop flowering.  Visual surface grazing and scarring of pod walls and stems will occur from DBM caterpillar feeding late season and this may result in a minor reduction of grain filling capacity depending on numbers of grubs, soil moisture levels and length of time to harvest.

Growers are urged to abide by label withholding periods for swathing/harvesting canola if applying a registered insecticide to control DBM (see the table below).

The pyrethroids (alphacypermethrin, esfenvalerate, gamma and lambda cyhalothrin) and carbamate (methomyl) registered for DBM are known to provide poor kill on DBM populations because of insecticide resistance.

Pesticide options for the control of native budworm and DBM can be found in DPIRD’s Winter/Spring Insecticide Spray Chart 2020.

For more DBM information refer to:

• DPIRD’s 2020 PestFax Issue 8 Native budworm and diamondback moths are being found across the wheatbelt article
• DPIRD’s Diagnosing diamondback moth page
• GRDC's Diamondback moth fact sheet
• GRDC’s Managing diamondback moth video.

For more DBM information contact Alan Lord, Technical Officer, South Perth on +61 (0)8 9368 3758 or Svetlana Micic, Research Officer, Albany on +61 (0)8 9892 8591 or Dustin Severtson, Development Officer, Northam on +61 (0)8 9690 2160.

Article authors: Cindy Webster (DPIRD Narrogin), Alan Lord (DPIRD South Perth), Svetlana Micic (DPIRD Albany).

Article input: Amber Balfour-Cunningham (DPIRD Northam) and Dusty Severtson (DPIRD Northam).