Slugs are slimy, soft-bodied, legless mollusks, built like snails with no shells. They can do damage to edible and ornamental plants by chewing through leaves, fruit and young plants. Let’s take a look at basic facts about slugs, their characteristics and preferences as well as actions we can take to minimize slug damage to our plants and crops.
Slug Basics
Slugs are typically grayish or brownish. Their head contains two sets of feelers: the upper set are their eyes and the lower ones are their smellers (see lead photo). Their size varies from ¼” to more than 4” long depending on the particular type. They are hermaphroditic, meaning that they contain both male and female reproductive organs. Their life starts as small round eggs that overwinter under plant debris, mulch, boards or in soil. They hatch in spring or early summer. They typically lay eggs at 2 years and can live as long as 6.
Slugs prefer cool, moist, shady environments. Their bodies emit a wet slime that protects them from desiccation or drying out. They feed off both ornamental and edible plants, including both fruits and vegetables and are most active from dusk to dawn and in full shade during rainy days when soils are moist. They prefer temperatures of 70 degrees or less, making spring and fall their most active periods.
Slugs have file-like mouth parts that scrape ragged holes in seedlings, plant leaves and soft fruit. Favorite foods include basil, beans, cabbage, corn, lettuce, strawberries, marigolds and many other herbaceous and succulent plants. Ragged holes are an indicator of slug infestation. Slime trails that create a moist surface that they can travel over are another indication of slug activity when the slug itself is not visible.
When they are not feeding, slugs congregate in sheltered places like under ledges, porches or decks, stone walls, mulch, garden debris and in the soil.
Actions to Help Manage Slugs
Basic preventive measures that can help manage slug invasions include:
- Slugs prefer cool, moist and shady locations. Reduce these conditions by:
- Pruning lower branches to allow more light penetration and reduce moisture
- Thin dense plant groupings to improve air circulation, add light and reduce moisture.
- Water early in the day to enable moisture reduction prior to darkness when slugs are most active.
- Remove slug gathering places like boards, containers, stones, cardboard etc. from garden areas. While we recommend mulching garden beds to maintain moisture and restrict weeds, temporarily removing mulch during periods of high slug activity may be necessary.
- Place traps from boards or other sheltering materials, like melon or grapefruit rinds or cabbage leaves, raised at one end to allow entry, where slugs can gather after their nighttime feeding effort. Inspect and remove slugs in the morning before they set out to find food. Drop them into soapy water and let them drown.
- Inspect plants with a flashlight after dark and pick slugs off the plants. Drown them as you would if finding them under the gathering locations described above. Watering the ground late in the day assures moisture and more slug activity when you plan a night raid.
- Use beer or a water plus yeast mixture in a pan or similar jar lid to lure them into the liquid, to drown them. Place the top of the trap flush with the soil surface and leave about an inch of space from the ground to the liquid to prevent escape. Monitor and remove dead slugs every morning. Place multiple traps in the garden to cover all the at-risk areas.
- Encourage predators like beetles, toads, snakes, birds and chipmunks that feed on slugs.
- There is some data that encourages making the soil surface difficult for slugs to slide across to reach their target plants. Materials mentioned include crushed eggshells, coffee grounds and wood ash. The effectiveness is not as clear as other actions mentioned. Ditto for spreading diatomaceous earth around plants to abrade the slugs protective mucus layer causing them to dry out and die over a few days.
- Copper tapes and strips are available at garden centers. They can be wrapped around plant stems or along the ground to prevent slug movement to or onto the plants. Apparently, there is an electrical reaction between the slugs and copper that repels slug movement. Be sure that the bands are at least an inch wide to prevent slugs from raising their bodies to cross over them.
- Slug baits containing iron phosphate can be sprinkled on the soil surface. Slugs consume it, lose mobility and die in 3-6 days.
Wrap Up
Slugs can be a destructive garden invader feeding off a broad variety of fruits, vegetables and ornamental plants. They are tricky to catch since they are most active after dark and at different times during the growing season. Also, recommended treatments may run counter to our normal practices, like mulching around plants. Nevertheless, there are a variety of actions gardeners can take to prevent or at least minimize slug damage. I hope the data included here is helpful and that the source listing below provides the guidance needed to identify the culprits and minimize any negative effects they may bring.
Sources:
Slugs in home gardens | UMN Extension
Managing Slugs in Crop Fields and Gardens – Maryland Grows (umd.edu)
Slugs are making tracks on my garden favorites! – MSU Extension
https://xtension.oregonstate.edu/sites/default/files/documents/12281/managingslugssnails.pdf
