Black Portuguese millipedes

Consultant, John Stuchbery (JSA Independent), has reported seeing significant numbers of black Portuguese millipedes (Ommatoiulus moreletii) in paddocks south of Ararat, in the Western district of Victoria. Up to 5-10 millipedes were found per m², sheltering underneath stubble and John says he found numerous dead millipedes where stubbles had been burnt. Black Portuguese millipedes have a smooth, cylindrical body made up of 50 segments when fully developed. Adults are 30-45 mm long, dark grey to black in colour and have 2 pairs of legs on each body segment. When disturbed they either curl up in a tight spiral or thrash about trying to escape. Black Portuguese millipedes congregate in large numbers and are quite mobile, especially after the first rains in autumn.

In the past we have received reports of black Portuguese millipedes causing damage to young canola seedlings. However, we have also heard of many instances where high numbers of millipedes are present in a paddock but no crop damage has occurred. Feeding damage is relatively rare and somewhat unusual, as millipedes predominantly live off organic matter such as leaf litter, decaying wood and fungi; they only occasionally attack living plants. There is some evidence that millipedes feed on crop plants when they are seeking moisture. Stubble retention and minimum tillage practices appear to favour millipede survival and numbers can to build up to very high levels in some paddocks under these conditions.

There are no insecticides registered against black Portuguese millipedes for use in broad-acre crops and it is unclear whether insecticide seed dressings help to prevent damage to emerging plants. Reducing the amount of stubble several weeks before sowing is probably the most effective option for limiting their numbers. In 1988, a parasitic nematode was released in parts of South Australia to provide biological control. The pest status of the Portuguese millipede has decreased in many areas in South Australia since that time, however it is unclear how widely the nematode has spread.