Discovering large numbers of the black Portuguese millipede (Ommatoiulus moreletti) congregating near establishing crops can be disconcerting. This species can build up to astonishingly high numbers.
While millipedes are primarily detritivores (feeders of decaying organic matter), which were once considered a low threat for farms, the black Portuguese millipede has gained pest status in the grains industry in southern Australia. Recent research and reports from growers and advisers to PestFacts south-eastern have shown that they can (but don’t always) feed on living crops.
Recently, large numbers of the black Portuguese millipede were reported in several paddocks in Victoria’s Northern Country, with some paddocks having to be resown due to feeding damage. Whilst undertaking fieldwork, Cesar Australia research scientist Sam Ward also noted unusually large congregations of this species in paddocks near Geelong and also southern NSW.
Challenges with the black Portuguese millipede
The black Portuguese millipede is a tricky pest to manage for three reasons.
Firstly, this species is not native to Australia. It is living here in an environment without its natural enemies and predators, allowing populations to thrive.
Secondly, crop stubble provides a cool, moist habitat and likely contributes to the build-up of millipedes. With the move towards retaining stubble-retained farming systems, creating an unhospitable environment for the black Portuguese millipede by disrupting stubble (e.g. tillage) is not a realistic option for many growers.
Lastly, the black Portuguese millipede is ground dwelling and mostly night active, evading insecticide sprays by sheltering during the day under heavy stubble loads and soil debris. There are no foliar or bare earth insecticide sprays registered to control this pest in grains.
Which crops are at risk?
If you are finding the black Portuguese millipede in paddocks with establishing crops, know that not all crop types are at risk of damage.
In microcosm feeding trials, when presented with lucerne, canola, lupin, lentil, chickpea, faba bean, wheat and oat seedlings, the black Portuguese millipede only damaged canola, lupin and lucerne plants.
Out in the field, over a decade of reports from growers and advisers to PestFacts south-eastern were mostly of damage to young canola.
Getting through establishment
Despite their presence throughout the entire winter-cropping season, the black Portuguese millipede is very much an establishment pest. Once crops get up and away, they are no longer at risk.
Research by our team has shown that some seed treatments can kill the black Portuguese millipede (see this study or contact us for more information), but seed treatments alone may not be enough to protect seedlings under a high pest pressure.
A dual insecticide and molluscicide bait (Transcend) containing the active ingredients fipronil and metaldehyde is registered to control the black Portuguese millipede in certain crops including canola and agricultural non-crop areas. Note that slug and snail baits containing metaldehyde alone will not kill millipedes.
In paddocks with high numbers of the black Portuguese millipede, you might consider sowing a high vigour crop variety at a higher seeding rate to help compensate for damage.
Other millipedes are about
The black Portuguese millipede may not be the only millipede species found on farms. Australia is home to many native species that are detritivores and are unlikely to be the cause of damage in crops.
For assistance distinguishing species, please contact our team at PestFacts south-eastern.
Thanks to Greg Toomey, Chris Dunn and Matt Nihill (Nutrien Ag), Sam Ward (Cesar Australia) and Mikaela Meers (Elders) for reports.