Description
Millipedes are not insects but arthropods. They are hard-shelled, cylindrical and approximately 2.5–5 cm (1–2 in.) long. They get their name (milli: thousands, pedes: legs) from having many legs — two short pairs of legs per body segment in the adult stage. Adult millipedes are dark reddishbrown to grey-black in colour and have hardened bodies. Immature millipedes look similar to adults but are white, have fewer legs and do not have hardened bodies. As they mature, they develop more legs and turn darker in colour. Another distinguishing characteristic is that they coil up tight when disturbed. Do not confuse millipedes with wireworms; wireworms are coppery-brown in colour and only have three pairs of legs.
Life Cycle
Both adult and immature millipedes overwinter in the soil under debris, rocks, etc. They can live for several years in the soil, taking up to 5 years to mature to the adult stage. They have become more prevalent with the adoption of reduced or no-till systems due to the increase in surface residues. Females lay their eggs in the soil near crop debris. Newly hatched millipedes begin with only 3–4 pairs of legs, adding more body segments and pairs of legs as they moult and grow to adult size.
Damage
Millipedes are typically beneficial. They help decompose organic matter and feed on other insects. However, when planting early in cool, wet springs, conditions are ideal for millipedes to feed on the swollen seeds and young seedling roots, particularly corn and soybeans.
No-till fields with residue and high organic matter are at greater risk, though damage has also been experienced in conventional fields. Deep planting can also promote injury. Droughty conditions will lessen their impact.
Note that millipedes may be found feeding on decomposing plants that are dead or dying from other causes such as herbicide injury.
Scouting
Inspect roots, germinating seed and soil around areas with gaps in the plant stand. Millipedes could be present on the roots or within the seed. If early-season injury is noticeable, but no pest is present, setting up wireworm bait stations will also be effective at capturing millipedes to determine their presence.
There is no action threshold for millipedes at this time.
Management Strategies
Insecticide seed treatments are not effective at controlling millipedes. No rescue treatments are currently available. Plant in ideal conditions to improve seed germination in these fields, particularly when cool, wet springs are forecasted.
