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High numbers of black Portuguese millipedes (Ommatoiulus morelettii) have been observed across paddocks in the Western district of Victoria. Agronomist, Justin Alexander (Agvise), has reported very high numbers in several canola crops, west of Lara. All paddocks contain a high stubble load and have been sown with untreated canola seed. In the worst affected areas where seedlings are moisture-stressed, whole plants have been killed. Black Portuguese millipedes mostly move and feed at night, and Justin says they have not been observed on plants during the day. Agronomist, Sarah Heazlewood (Gorst Rural Supplies), also reports observing high numbers of millipedes in paddocks around Lake Bolac, particularly where a large amount of trash/stubble residue was present.
Feeding damage in broad-acre crops from black Portuguese millipedes is unusual as they generally feed on organic matter and are not favoured by relatively bare soil conditions at seeding. However with the increase in minimal tillage and stubble residue retained on the soil surface across many regions, conditions for breeding have become more favourable. There have been suggestions that they attack crops to obtain water when moisture is limited.
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. Portuguese millipedes congregate in large numbers and are quite mobile, especially after the first rains in autumn. There are no insecticides registered against Portuguese millipedes. Reducing the amount of stubble residue 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.
For further information and images of Portuguese millipedes, click here.
What is PestFacts?
PestFacts south-eastern keeps growers and advisers informed about invertebrate pests and beneficials in broadacre crops and pastures during the winter-cropping season in Victoria and southern New South Wales.
PestFacts south-eastern is run through IPMforGrains: Best Practice Insect Pest Management, a project delivered by the National Pest Information Network (cesar, DPIRD, QDAF, NSW DPI, and SARDI). This project aims to provide grain growers and advisors with information on invertebrate grain pest occurrence and equip industry with the knowledge needed to implement integrated pest management practices. This initiative is a GRDC investment and includes in-kind contributions from all project partner organisations.
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PestFacts is produced on an ʻas-needsʼ basis and relies upon pest observations and field reports from our subscribers. If you have recently observed invertebrate pests (or beneficial species) in broadacre crops, please contact us to report your observations.
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