The Q&A Archives: Radish roots deformed, with small worms

Question: My radishes grew well last season, but when I harvested them, the roots were deformed and had small worms in them. What are these insects and how do I control them? W.S. Swartz Devison, MI

Answer: Your radishes had cabbage maggots, says Tim Stebbins, Master Gardener coordinator at Michigan State University in East Lansing. After overwintering in the soil as a pupae, the adult fly emerges in April and lays white eggs at the base of the stem of young radishes, turnips, broccoli, cabbage and other cabbage family crops. The eggs hatch in three to five days, and the young larvae burrow into the plant roots. Cabbage maggot flies can have two to four generations a year, infesting fall crops as well asspring crops. The best control for a home gardener is to plant under a floating row cover in early May before the adult fly lays its eggs, Stebbins explains. Once the larvae hatch and tunnel into the roots, there's little you can do to stop them. If the bed is covered, however, the fly won't be able to find the plant and deposit its eggs, he notes. If you spread manure, use only well aged manure and till it into the soil a few weeks before planting, adds Stebbins, noting that the adult fly prefers to lay eggs in moist, highly organic soils. And it overwinters on cole crop debris, so cleaning up and composting such materials will lessen the problem.

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