Ask a Master Gardener: Nontoxic options available to fight slugsHave a gardening question? This question has been answered by St. Louis County Master Gardeners, who have been trained by the University of Minnesota as volunteer horticultural educators. Questions can be submitted and additional information found at www.extension.umn.edu/garden.
Q: Something eats holes in my hosta every year. I never see any bugs. Is there a nontoxic insecticide I could try spraying?
A: Well, there’s no such thing as a nontoxic insecticide. If it kills things, it’s toxic. Insecticides differ, so it’s not possible to choose one without knowing what the pest is. This year, you may have cutworms, but since this is a perennial problem, the likely culprit is slugs.
Slugs and cutworms leave similar damage on leaves, and both will eat hostas. You may be able to determine for sure which you have if you go out at night and scout with a flashlight. Slugs may leave telltale slime trails on nearby sidewalks early in the day.
Slugs like it cool and moist, so you can make your garden less friendly to them by watering only in the morning and letting things dry out by afternoon. You also can remove slug habitat. Keep mulch to no more than 3 inches. Prune lower leaves and don’t let the garden get too crowded.
To trap slugs, lay out damp newspaper or boards, look underneath in the morning, and pick off and kill the slugs. You can trap slugs with beer, too. Set a soup can with its rim flush with the ground and fill to about an inch below the top. Use the cheap stuff. Slugs aren’t beer snobs.
Contrary to popular myth, crushed egg shells don’t deter slugs. Diatomaceous earth may help if it’s kept dry.
There also are slug repellents and slug-killers you can buy, but note that metaldehyde can kill pets and wildlife.
If you’d rather not bother with all that, you can try plants that like shade but don’t attract slugs, such as astilbe and bleeding heart (dicentra). More information and a list of substitute plants is at www.extension.umn.edu/distribution/horticulture/dg7561.html.
More info on cutworms is at: http://blog.lib.umn.edu/efans/ygnews/2012/07/vareigated-cutworm-damage.html.