Slugs in Iowa are always a problem, especially for shade-loving plants like hostas, but during a wet year like this, there are a lot more of them, doing a lot more damage.
Hostas are their clear favorite. This late in the season in Iowa, there are hardly any hostas that don’t have some slug damage. But these small slimy relatives of the snail also like just about any large, tender leaf, including lettuces. Another slug favorite is ripening fruit or veggies, especially those close to or touching the ground, such as melons, tomatoes and strawberries.
You can tell you have a slug problem by closely inspecting the damaged leaves. Slugs make irregular holes with smooth edges that are usually larger than a pencil eraser and smaller than a quarter. The damage tends to be within the leaf blade instead of along the edges. (Most other chewing insects will eat from an edge and destroy much larger areas.)
How to control slugs? Here’s a three-pronged approach to slug control from Iowa State University Horticulture Extension. Unlike some other slug remedies, these are all scientifically proven through non-biased university research. None will keep your plants completely free from slug damage, but they will control the extent of the problem.
Prevent Slugs In the First Place
As much as possible, make your garden a place slugs don’t like. They require moist soil to lay their eggs and cool, moist, sheltered sites to hide in during the day. So open up the garden to allow more sun and air circulation. Cut back trees and shrubs to let in the light. Keep mulch to a minimum — no more than 1 inch. Since slugs also feed on decaying plant material, do not mulch with fresh grass clippings in areas where slugs are a problem. Instead opt for gravel or stone that doesn’t break down rapidly. Rake leaves from the garden beds in fall.
Trap boards with wet newspaper, cardboard, or carpet samples, about a square foot in size. Place these near or right under plants where slugs have been feeding. After a couple of days, check the underside of the traps and remove and destroy the slugs that have gathered there to hide by putting them into a bucket of salty water, which will kill them. Inverted melon rinds set on the soil also will attract slugs.
Or create a beer trap. Fill a shallow container, such as a yogurt cup, with beer. Then bury to within a half inch of the rim. Slugs will find it irresistible, crawl in and drown. You may want to put a loose cover over the beer trap to shade it and prevent rain from diluting it.
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Consider Commercial Slug Killer
If you choose to use non-organic measures in your garden, consider a commercial slug bait. Follow package directions exactly for best results and safest use, including directions for disposal.
Usually, slug baits should be used in the spring or fall when slugs are active. It is a good idea to irrigate before applying a bait to promote slug activity and then apply the bait in the late afternoon or evening. Many baits contain metaldehyde. Although it is effective, it has its faults. It is rapidly inactivated by sunlight and water so it has to be reapplied frequently. It cannot be used in vegetable gardens and can be toxic to pets that ingest it.
Alternative baits are available that contain iron phosphate (ferric phosphate) as the active ingredient. Trade names include Sluggo, Escar-Go!, Schultz Slug and Snail Bait and others. Although some experts consider iron phosphate baits to be slightly less effective than baits containing metaldehyde, they do have several advantages. They can be used more effectively in wet conditions because iron phosphate doesn’t readily dissolve in water; they can be used around edible crops; and they do not pose a threat to pets, birds and other non-target species.
l Veronica Lorson Fowler is co-publisher of The Iowa Gardener website at www.theiowagardener.com.