Black Portuguese millipedes

Black Portuguese millipedes are on the move, and causing concern in many areas that received early autumn rainfall.

 

Where have they been reported?

Huge numbers of millipedes have been reported south of Forbes, in the Central West Slopes & Plains district of NSW and across North East Victoria, particularly between Shepparton and Yarrawonga, since early April (thanks for the reports!*). In one instance in NSW, populations of >1000 per m2 were decimating volunteer canola prior to the paddock being sprayed out and replanted to wheat. The prospects of the damage being transferred to the wheat seedlings was concerning. In other cases, large numbers were evident prior to sowing, particularly in paddocks with heavy stubble loads.

More generally, there are reports of vast numbers of millipedes entering homes throughout Victoria and NSW, but only because of their attraction to light.

Millipede habits and behaviour

Black Portuguese millipedes (Ommatoiulus moreletii) have emerged as a sporadic but significant pest of crops, particularly canola, in the last 5 years. This pest is almost certainly linked to paddocks with high stubble loads and minimum tillage, and they become very active when the soil is moist. Although black Portuguese millipedes will attack seedlings, there are many instances where high numbers of millipedes are present in a paddock but no crop damage occurs. Feeding damage is relatively rare because millipedes predominantly feed on organic matter such as leaf litter, decaying wood and fungi.

Millipedes congregate in large numbers and are quite mobile especially after autumn rainfall. The early autumn rains experienced in southern NSW and northern Victoria this year provide perfect conditions to mobilise the previously inactive adult millipedes. Millipedes have a two year lifecycle, suggesting that the current generation began in autumn 2012. Adult females lay eggs into the soil during autumn or early winter. When juveniles hatch from eggs they are immobile and legless.

Our advice

Monitoring of canola paddocks with high numbers of millipedes is recommended. Be sure to distinguish millipede damage from that of other pests, such as slugs. If millipedes are found within paddocks, a night time visit will help determine if they are feeding on crop plants - as millipedes are mainly active and feed at night. During the day, it is best to search under rocks, stubble residue, wood, or to dig up the soil with a spade. Refuge traps such as carpet squares, tiles or pot plant bases can be used to detect millipedes.

Control options

Cultural options to reduce damage in crops include early establishment, use of higher vigour varieties and increasing seeding rates. Removing stubble and trash several weeks before sowing is likely to be the most effective option for limiting numbers, but this is less viable at this time of the year. There are currently no insecticides registered against black Portuguese millipedes in broad-acre crops. Field reports suggest fipronil seed treatment may be helpful, but it is not registered for this use.

Description

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. For assistance with identification of millipedes click here.

* Source of field reports of black Portuguese millipedes

Jim Cronin - Agronomist, Landmark (NSW Central West Slopes & Plains)

Bruce Larcombe - Agronomist, IK Caldwell (NorthEast Victoria)

Paul Umina & Garry McDonald - cesar