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Wireworms and Millipedes on Root Vegetables - Which is which?

Until recently, wireworms and grubs have been thought to be the main soil insects affecting root vegetables in Ontario. In contrast, millipedes have generally been considered beneficial due to their habit of feeding on decaying plant material, which helps to incorporate organic matter into the soil. However, under favourable conditions (e.g. cool, wet soil that is high in organic matter), millipede populations can build to high levels and possibly damage the roots and seedlings of a variety of crops. In recent years, millipedes have become an increasing problem in field corn grown under no- or low-till cultivation. Millipedes have also been observed causing substantial damage to ginseng seedlings and, in the last two growing seasons, we have found large populations of millipedes in root vegetables where crop damage was originally attributed to wireworms.

Could millipedes be a new pest of root vegetables in Ontario, or perhaps secondary feeders entering these crops after they have been damaged by other pests? Unfortunately we don't yet fully understand what role millipedes play in causing damage to these crops, however a project, funded by a Canada-Ontario Research and Development Program grant from the Fresh Vegetable Growers of Ontario and conducted by University of Guelph researchers and OMAFRA staff, is currently underway to study soil pests in root vegetables. Results are not yet available, but we hope to have some answers in the near future.

In the meantime, be aware that wireworms and millipedes are often mistaken for one another. Here is a quick guide to some of the key differences between the two.

Figure 1 - Millipede. Note the number of legs. This is a key characteristic to use when distinguishing millipedes from wireworms.

Figure 2 - Wireworm. Note that there are only 3 legs located on the middle portion (thorax) of the body.