How to Control Slugs

This article discusses some tactics for keeping slugs out of your crop.
How to Control Slugs - Articles


Slugs are actually mollusks. There are a few different species of slugs in Pennsylvania. Some are small; others can reach up to 8 inches long. They overwinter as eggs, immature or mature slugs in protected areas in fields, including under boards, plastic or decaying vegetation. Slugs are especially troublesome in no-till fields with lots of crop residue. Slugs become active in the spring, continue their life cycle, and when mature they can lay up to 80 spherical, pearly white eggs at a time. They can lay eggs up to 6 times a year.

Slugs damage plants by chewing holes in leaves and fruit. They leave silvery mucous trails where they travel, which is certainly unappetizing on herbs and lettuce. One of their worst habits is their tendency to inhabit the inside lower leaves of head lettuce. Once they have moved into your crop it is just about impossible to wash them all off which can significantly decrease your yield.

If you can prevent the slug population from moving into your crop, you will be able to extend your marketing season. It is critical to start early because after the population builds it is really hard to stop them. Here are some ideas for controlling this pest:

  • Sanitation - remove all overwintering sites and resting areas prior to planting. This includes loose boards, plant residue and stones.
  • Traps - set out boards or damp burlap bags in the evening. Slugs are mostly nocturnal and they will hide under the traps in the morning, so you can destroy them
  • Natural enemies - Encourage toads, garter snakes, ground beetles. They can be helpful, but are not reliable to completely control slugs.
  • Diatomaceous earth - comes from fossilized mineral deposits of the silica-containing cell walls or "shells" of once living aquatic algae called diatoms. This mineral, diatomite, is mined in open pits out west, and then chunks of the mineral are pulverized into a flour-like powder. The diatom fragments have sharp microscopic glass-like edges that abrade the outer water-protecting cuticle of the pest causing it to lose water and further dries out pests by absorbing protective fats and oils. It can discourage slug populations under dry conditions, but must be reapplied if it gets moist.
  • Iron phosphate - sold as a granular product. It acts as a stomach poison in slugs and snails by damaging their digestive tissue. Several formulations are allowed by the Organics Materials Review Institute.
  • Metaldehyde - a pelleted pesticide used to attract and kill slugs by destroying their mucus production thus reducing their mobility and digestion. This is the most toxic choice for slug control and should be used only as a last resort.

Other Resources

If you choose to use pesticides, always follow the directions on the label.