I recently had a call about millipedes feeding on corn kernels in northeast Iowa this week. The farmer had a 120-acre cornfield with approximately 20 percent stand loss associated with millipede feeding. I rarely hear about millipedes as field crop pests, but a couple factors likely played a part in this situation. The only time I hear about millipede infestations is when the soils are cool and wet, and often in fields with high residue. The same could be said about isopods, slugs, and snails – and the growing conditions that tend to favor these pests. Part of the reason we would see feeding injury in these cases is seeds are not germinating quickly after planting or seedlings are growing slowly, and feeding can seriously impact plant development.
Millipedes are considered a slow-moving nuisance pest that feeds on decaying organic matter. They range in body size (1/4 to 1 1/4 inches long) and are usually dark in color. They generally have a round body, as compared to the flattened body of a centipede. Millipedes have a pair of antennae, reduced chewing mouthparts that scrape food, and most segments would have two pairs of legs. Sometimes they can be confused with wireworms.
The management of millipedes typically involves cultural control, as insecticides do not provide protection to seeds and seedlings. This should make sense, as millipedes are not insects. A later date of planting with warmer, dryer soils would promote vigorous plant growth that would limit serious millipede injury. Tillage in particularly infested areas could help dry out the soils and diminish millipede populations.
Random fact: Millipedes are arthropods within the class Diplopoda. They are distant relatives to insects and arachnids. People who study millipedes are called diplopodologists. I thought “entomologist” was hard enough to understand!