- Slugs are slimy, soft-bodied animals, described as shell-less snails.
- They are present from spring to fall, in cool, moist areas with shade.
- Slug population increases during rainy season and on well-irrigated gardens.
- Slugs feed on leaves of many plants (especially seedlings), ripening fruits and vegetables, and decaying plant matter.
- They feed at night and hide during the day.
- Slugs create irregular holes on leaves and fruit and affect the appearance of the plant.
- Extensive feeding can result in a weak or dying plant.
- Baits and pesticides can be used to control slugs, along with other methods like setting traps and barriers.
How to identify slugs
Slugs can be described as snails without shells. They are related to clams and oysters.
- Slugs are slimy and soft bodied, without any legs.
- They are generally brownish or grayish.
- Their head contains two pairs of feelers — a larger pair above carries the eyes and a lower pair below is used for smelling.
- They can range in size from 1/4 inch to two inches or longer.
The presence of slugs in your garden can be checked by looking for signs of slug movement or slug feeding. They may be seen at night or during the day in cool, shaded sites.
Slugs produce slime and use the slime to move. If you see a dried slime trail, it could mean that slugs are active in your garden.
Life cycle of slugs
In Minnesota, slug eggs can live through the winter.
- In the fall, slugs lay their translucent eggs under plant debris, mulch, boards or in the soil.
- Eggs hatch the following spring and slugs start feeding on strawberries in spring and early summer.
- Slugs have a layer of slime to protect their skin from drying up.
- When they move, they leave a slime trail which can be used to identify their presence.
- Slugs have a structure called the radula, which contains small teeth and damages fruit. The radula scrapes or cuts food before eating it.
Damage caused by slugs
Slugs use file-like mouthparts to rasp and chew plant tissue. Because of their mouthparts, they create irregularly shaped holes in leaves and fruit.
- In cases of severe damage, complete defoliation of young plants could occur.
- Slugs can create holes of varying size in fruit.
- The damage can be unnoticeable scraping on the surface of the fruit to significant cavities equal to half of the fruit.
- When present in large numbers significant damage can be done to fruit.
How to protect your garden from slugs
If slugs are a problem in your home garden, it is best to use a variety of steps to reduce their numbers.
- Check for slugs during the day by looking for slime trails in your garden.
- Be extra cautious during periods of cloudy and rainy weather.
- The number of slugs in any season depends on how moist the growing conditions are.
- In the evening use a flashlight to check for slugs.
Rake your garden in early spring to remove leaves, plant debris and slug eggs
- Remove mulch and leaf litter near plants as these can be potential hiding places for slugs.
- It is important to do this in early spring to remove any slug eggs that may be present.
- Also remove boards and other material to reduce favorable areas for slugs.
- Avoid using large wood chips as they provide hiding places for slugs.
- If you maintain wood mulch for weed prevention, keep only three inches near the plant themselves.
Water your garden only when necessary
Slugs do not like warm, dry conditions.
- Water your plants in the morning, so that plants are dry by evening (when slugs become active).
- Place drip irrigation tape close to the plants and avoid creating wet mulch situations.
- Take the following steps to keep the soil surface dry:
- Thin or divide plants if they are too crowded.
- Prune lower leaves or stake large plants to allow better air circulation.
- If you plant in rows, keep the width of the rows narrow (12 to 18 inch).
Choose plants that are not attractive to slugs
Plants that perform well in shade but are less desired by slugs include astilbe, dicentra, lobelia, ranunculus, vinca and viola.
Plants for areas with partial shade: phlox, campunula, hemerocallis and mentha.
Mentha, ranunculus and viola spread vigorously and may not be suitable for some sites.
- 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 in high numbers).
- Be sure to put out enough traps to protect the entire garden.
Set out several flat boards, shingles or damp newspapers
Check under these traps the next morning and kill any slugs that are hiding. Repeat this step night after night until the slug damage is no longer present.
Handpick slugs off plants
You can drown slugs in soapy water, crush them or spray them with household ammonia diluted to a 5 percent or 10 percent solution.
Use jars, cans, pans or similar containers
Bury containers into the ground so the top of the container is level with 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.
Copper is an effective barrier for slugs
Copper strips or tape sold specifically for slug control can be purchased from garden suppliers. Copper barriers are most practical for small gardens and containers.
Caution: The sharp edges of some products may cause safety problems, especially for young children.
Diatomaceous earth as a slug barrier
Diatomaceous earth (tiny fossilized skeletons of ancient aquatic diatoms) is coarse and can scratch up slugs. It is most effective when used in dry conditions and has little effect when it absorbs moisture. It is not as effective as a copper barrier.
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.
If pesticides are used, natural enemies might be affected and can no longer feed on slugs.
If you have to use chemicals for other issues, spot treat small pest problems or use baits.
Baits and pesticides can be used in combination with a few other control methods. Baits are not effective in controlling slugs, if used alone.
Baits should be applied before fruits (especially berries) become ripe, because the slugs might prefer ripe fruit over slug bait.
- Irrigate the patch just before applying a bait. This will create an ideal condition for slugs to become active.
- Apply the bait in the late afternoon or evening close to the time when the slugs will begin activity.
- Sprinkle some bait in areas where slugs might be hiding (close to walls or fences).
Metaldehyde is an ingredient for baits, and is available as a granular or liquid paste.
- Apply it to the soil near slug-infested plants.
- When metaldehyde is eaten by slugs, it destroys their ability to move and digest food.
- Metaldehyde is more effective during warm, dry weather.
- It is most effective when applied after a rain storm but when sunny weather is expected.
Iron phosphate, 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.
- Iron phosphate baits are safe to be used around children and pets.
- Iron phosphate kills more slowly than metaldehyde and the slugs will seek a hiding place and die there.
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, because slugs will avoid baits contaminated with copper products.
CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.
Be sure that the fruit/vegetable you wish to treat is listed on the label of the pesticide you intend to use. Also be sure to observe the number of days between pesticide application and when you can harvest your crop.
Reviewed in 2018