Diamondback moth numbers remain low
- Mingenew
- Mukinbudin
- Merredin
- Kellerberrin
- Howick
Diamondback moth (DBM) caterpillars and moths are continuing to remain in low numbers late into the season across all grainbelt areas.
Widespread surveillance for DBM in canola focus crops is being conducted until the end of the season as part of a Grains Research and Development Corporation (GRDC) funded project on DBM surveillance.
DBM caterpillar numbers are currently well below threshold, although many crops are experiencing moisture stress. Growers are urged to monitor canola crops for DBM and native budworm caterpillars.
Dave Nicholson (DPIRD) found 3to 10 caterpillars per 10 sweeps in podding canola at Dandanning (Mukinbudin).
Rachael Minett (Primaries CRT) found less than one caterpillar per 10 sweeps in early flowering canola at North Howick.
Mingenew Irwin Group (MIG) found an average ranging from 0 to 2 caterpillars per 10 sweeps in five canola focus crops in the Mingenew area.
An average of less than one caterpillar per 10 sweeps was found at the following DBM surveillance sites in the last fortnight: Merredin, Kellerberrin and Mukinbudin. No caterpillars were recorded at Geraldton, York, Corrigin, Kondinin, Narembeen, Albany, Esperance, Dandaragan, Wickepin, Kalannie and East Wubin.
Moth trapping update
- Usual trapping locations
The number of moths captured in pheromone-baited traps over the last fortnight were highest at: Nolba (67 moths), Marrah (59), Dandanning (56), Yallabathara (44), Kondinin (36), Perillup (31), Dandaragan (31), East Wubin (26), Moonyoonooka (25), Daadenning Creek (Kellerberrin) (25), Kalannie (20), Wicherina (16), Hyden (11) and North Mingenew (10).
Management
DPIRD's Seasonal Climate Outlook report is predicting high chances of warmer temperatures and reduced rainfall for the August to October period. Canola plants are more vulnerable to caterpillar damage when they are stressed due to dry conditions and when they are flowering.
DBM thresholds for control at late flowering (no moisture stress) are 100 or more per 10 sweeps and 150 to 200 caterpillars per 10 sweeps at pod maturation.
Some other helpful tips to consider when sweep netting crops are:
- A high proportion of small caterpillars (less than 3 mm) in a sample often indicates that caterpillar numbers will increase further.
- Regular assessments of the number of caterpillars in the crop are required because the numbers can fluctuate and are just as likely to decrease as they are to increase at any stage throughout the growing season. Caterpillar numbers may reduce in both cool, wet and windy conditions or fine and mild weather.
- When checking crops with a sweep net, be mindful that small native budworm caterpillars can easily be confused with DBM caterpillars in canola crops. DBM caterpillars are usually pale yellowish green and tapered at each end of their body and grow to about 10 mm long. They often wriggle rapidly when disturbed and will hang on a silken thread. Native budworm caterpillars are far more damaging as they grow to larger sizes (up to 40 mm long) and will chew into the pods.
DPIRD research trials have showed that late season application of insecticide (especially multiple sprays) against DBM is less likely to result in a profitable outcome than early and mid-season pest control. This is mainly because DBM have less impact on yield once crops stop flowering. Visual surface grazing and scarring of pod walls and stems will occur from DBM caterpillars feeding in the late season. This may result in a minor reduction of grain filling capacity depending on the number of caterpillars, soil moisture levels and length of time to harvest. For this reason, the threshold of DBM numbers required to justify spraying will increase over time.
Growers considering late applications of insecticides need to be mindful to adhere to label withholding periods prior to swathing/harvest. Pesticide options for the control of DBM can be found in DPIRD’s 2023 Winter Spring Insecticide Guide.
New product registered for DBM in canola
Growers and agronomists should be aware that the active ingredient cyantraniliprole is now registered for use on DBM in canola.
More information
For more DBM information refer to:
- DPIRD’s diagnosing diamondback moth
- GRDC's fact sheet diamondback moth
- GRDC’s video managing diamondback moth.
For more information contact Research scientist Svetlana Micic in Albany on +61 (0)8 9892 8591 or Technical officer Alan Lord in South Perth on +61 (0)8 9368 3758.
Article author: Bec Severtson (DPIRD Northam).