Slugs in Home Gardens

Jeffrey Hahn, Assistant Extension Entomologist
Jody Fetzer, Integrated Pest Management Coordinator

Copyright ©  2008  Regents of the University of Minnesota. All rights reserved.

Slugs can be very damaging pests in moist, shady gardens. They feed on the leaves of many plants, especially seedlings. Later in the season they can feed on ripening fruits and vegetables. Slugs are especially numerous during rainy seasons and in well-irrigated gardens. If slugs are abundant one year, it does not mean they will be as common the following season; the relative number of slugs in a given season depends on how moist the growing conditions are.

Identification

Slugs are best described as snails without shells. They are a type of mollusk, related to clams and oysters. Slugs are soft bodied, generally brownish or grayish, with eye stalks. They vary in size from 1/4 inch to two inches or longer. Slugs leave a silvery slime trail that they secrete as they move.

Slugs use file-like mouthparts to rasp and chew plant tissue. Because of their mouthparts, they create irregularly shaped holes. Feeding damage can be cosmetic, however extensive feeding can result in plant stress or even death.

Biology

In Minnesota, slugs usually overwinter as eggs in protected sites on the ground, such as under plant debris, mulch, or boards. Eggs hatch during spring or early summer. Depending on conditions, slugs may lay eggs throughout the summer. Slugs are more active at night and when it is cool and damp, although they may be seen during the day in cool, shaded sites. Warm, dry conditions are less favorable to them.

Management

If slugs are a problem, it is best to use a variety of tactics to reduce their numbers.

Cultural

Rake your garden in early spring to remove leaves, plant debris and slug eggs. Also remove boards and other material to reduce favorable areas for slugs. Avoid using large wood chips as they provide hiding places for slugs. Do not place mulch any thicker than three inches. This helps protect plants from weeds and helps maintain plant moisture while minimizing a favorable environment for slugs.

Water your garden only when necessary. Irrigate in the morning so plants are dry by evening. Prune lower leaves or stake large plants to reduce potential hiding places for slugs and to allow better air circulation that helps keep the soil surface drier. Thin or divide plants if they are too crowded.

Some plants have been observed to be less affected by slugs.

A list of those that do well in shaded areas includes

• Astilbe,
• Dicentra,
• Lobelia,
• Ranunculus,
• Vinca, and
• Viola.

Plants resistant to slugs that grow well in partial shade include

• Phlox,
• Campanula,
• Hemerocallis, and
• Mentha.

Unfortunately Mentha, Ranunculus, and Viola spread vigorously and may not be suitable for some sites.

Trapping

Trapping and handpicking helps lower slug numbers. To be effective, traps must be checked and cleaned out several times a week (more when slugs are abundant). Be sure to put out enough traps to adequately protect the entire garden.

You can trap slugs by setting out several flat boards, shingles or damp newspapers. Check under these traps the next morning and kill any slugs that are hiding. You can drown slugs in soapy water, crush them, or spray them with household ammonia diluted to a 5 percent or 10 percent solution. Traps containing beer or other fermenting food are popular. You can purchase commercially available slug traps or make your own. Sink jars, cans, pans or similar containers into the ground so the top is level with the ground (some commercially available traps are placed on the ground). Pour beer or a water and yeast mixture (one teaspoon of yeast to three ounces of water) or similar fermenting liquid into the container. Slugs are attracted to the odors, fall in and drown.

Barriers

Copper is an effective barrier to slugs. Copper strips or tape sold specifically for slug control can be purchased from garden suppliers. Caution: The sharp edges of some products may cause safety problems, especially for young children. Copper barriers are most practical for small gardens and containers.

Diatomaceous earth (tiny fossilized skeletons of ancient aquatic diatoms) is moderately effective as a slug barrier. When slugs come in contact with diatomaceous earth, it is abrasive to their skin. Diatomaceous earth is most effective when used in dry conditions and has little effect when it absorbs moisture.

Biological

There are many types of animals that feed on slugs, such as beetles (e.g. ground beetles, rove beetles, fireflies), toads, snakes, turtles, shrews, ducks, starlings and other birds. To maximize the effect of natural enemies, minimize the use of chemical pesticides. Reduce chemicals by spot treating small pest problems, using baits, and avoiding unnecessary pesticides applications.

Chemical

There are several pesticides that may be used to supplement the above nonchemical tactics. Iron phosphate (e.g. Escar-Go, Sluggo), applied to the soil as granules, is a less toxic bait for slugs. Iron phosphate is mixed with a food product that draws slugs to the bait. Once slugs consume this bait, they stop feeding and die three to six days later.

Chemical slug baits often contain metaldehyde (e.g. Deadline, Defender), available as a granular or liquid paste. When metaldehyde is eaten by slugs, it destroys their ability to move and digest food. Apply it to the soil near slug-infested plants. Metaldehyde is more effective during warm, dry weather. It is best to apply metaldehyde after a rain storm but when sunny weather is predicted.

Copper compounds (copper silicate and copper sulfate) are effective repellents. They are usually mixed with water, then sprayed on plants. Copper products repel slugs but do not usually kill them. Do not spray copper compounds near baits; slugs will avoid baits contaminated with them.

Caution: Always use insecticides strictly in accordance with label statements and directions. The plant(s) to be treated need to be listed on the product either specifically or as part of a broader listing of plants. If suggestions in this publication contradict label recommendations, the label is the final authority on how to use that specific product.

Photo Credits
Photo 1, Jeff Hahn
Photo 2, Department of Entomology, University of Minnesota

Produced by Communication and Educational Technology Services, University of Minnesota Extension.

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