Millipedes are considered beneficial in vegetable production due to their habit of feeding on decaying plant material, which helps to incorporate organic matter into the soil. However, under certain conditions millipede populations can build to high levels and may damage roots and seedlings of a variety of crops. In recent years, millipedes have become an increasing problem in a number of Ontario crops, including no/low-till field corn and ginseng.

Over the last few years, we have seen crop damage and correspondingly found large numbers of millipedes in root vegetables. At the time, we did not have sufficient information to know whether millipedes were emerging as a new pest of root vegetables in Ontario, or whether they were simply secondary feeders entering these crops after being damaged by other pests. In the summer of 2007 a collaboration between University of Guelph researchers and OMAFRA staff was initiated to address the role of millipedes as a potential pest of Ontario root crops.

Sampling was conducted in 2007 in sweet potato and carrot fields in southwestern Ontario. Our goal was to determine the seasonal dynamics of millipedes throughout the season, and to evaluate different monitoring methods. Three trap types were evaluated: (1) a buried piece of white potato; (2) a buried mesh bag of pre-soaked corn; and, (3) a pitfall trap. All traps were changed on a weekly basis. At the end of the season, sweet potatoes and carrots were harvested from each sample site and assessed for pest damage.

What did we see…

·   Millipede populations varied considerably among fields.

Based on this preliminary research, it appears that millipedes can act as both primary and secondary pests in carrots and sweet potatoes. Are they new pests? It's hard to say, but it's likely that they have caused damage in the past, but that damage may have been mistaken for wireworm or grub damage. It's important to keep in mind that millipedes are still beneficial in most of your fields - remember that of 10,000 known species, only three were found to be problematic in our study. More research will be needed to determine what population levels can cause economic damage to a crop, what field conditions contribute to the development of those populations and to identify effective control measures. Currently, there are no pesticides registered for use against millipedes in Canada.

This research was funded by the Canada-Ontario Research and Development Program, an initiative of the federal-provincial territorial Agricultural Policy Framework and the Fresh Vegetable Growers of Ontario. Thanks to Drs. Sears and Hallett, L. O'Keefe and T. Marrowa of the University of Guelph and all cooperating growers who collaborated on this project.

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