Slugs are among the first creatures to become active in spring. They scrape their mouthparts across leaves, stems, and flowers to ingest plant tissue. Shade gardens are ideal habitats for slugs, along with mulched areas containing bedding plants. New transplants and small seedlings are especially vulnerable to these creatures. Feeding damage and silvery slime trails are already apparent on bedding plants (Figures 1 & 2).
Soft-bodied slugs require cool, humid conditions, so they usually feed at night and hide during the day. They can be difficult to manage if the conditions that favor them remain unchanged.
Here are tactics to reduce problems with slugs. Combining several will be more successful than relying on only one.
Sanitation—Keep the area free of plant debris (leaves, pulled weeds, etc.) and decorative objects on the ground that provide cool moist hiding places.
Manage moisture—Water in the early morning when necessary so that the foliage and soil surface are as try as possible in the evening when slugs are active. Use drip irrigation with water directed toward the ground near individual plants
Promote sunlight and air movement—When practical, prune or remove low foliage, especially leaves touching the ground. Avoid use of excess mulch to allow drying.
Consider plant selection—When possible, plant begonias, geraniums, impatiens, and other plants that slugs do not prefer.
Traps—Bury small, shallow containers of beer so they are even with the soil surface (Figure 3). Slugs will be attracted to this trap and drown. Change the beer as needed.
Provide limited shelter—Lay a few objects (overturned flower pots, pieces of cardboard, wood, flat rocks, etc.) flat on the ground. Slugs hiding under them during the day can be collected and destroyed (drop in soapy water). Be sure to remove competing sites.
Barriers—Diatomaceous earth, wood ash, lime, sawdust, or copper striping, can be used to protect areas that are slug-free.
Slug baits are usually metaldehyde or iron phosphate. Some formulations also contain an insecticide.
Metaldehyde—kills slugs and snails by absorption or ingestion. The chemical causes them to “mucous-out” which immobilizes them and causes dehydration. This active ingredient affects the central nervous system so it is toxic to many organisms that ingest it. Some products contain Bitrex, recognized by the Guinness Book of Records as the world’s most bitter substance. As a safety measure, precautions should be taken to prevent accidental ingestion by humans and non-target organisms.
- Ortho Bug-Geta Granular Snail and Slug Killer (3.25% metaldehyde + Bitrex) kills snails and slugs within 1 to 3 days and remains effective after rain or sprinkling for up to 3 weeks. It is labeled for use around vegetables, fruit trees, citrus, berries, ornamentals, shrubs, flowers, trees, lawns, gardens, and in greenhouses.
- Ortho Bug-Geta Plus Granular Snail and Slug Killer (2% metaldehyde + 5% carbaryl + Bitrex) kills snails and slugs, plus ants, cutworms, armyworms, earwigs, sowbugs, crickets, pillbugs, grasshoppers, and millipedes. Do not allow this chemical to come in to contact with, and contaminate, edible parts of plants.
Iron phosphate—causes slugs and snails to stop feeding and become less mobile after ingesting iron phosphate bait. They usually die within 3 to 6 days. This active ingredient is OMRI-listed.
- Sluggo Slug and Snail Bait, as well as Bayer Advanced Natria Snail & Slug Killer Bait (1% iron phosphate), are labeled for use in or around all food commodities and may be used up to, and including, the day of harvest.
- Bug-N-Sluggo Insect, Slug and Snail Bait (0.97% iron phosphate + 0.07% spinosad). This product kills ants, earwigs, cutworms, pillbugs, in addition to slugs and snails.
General Slug Bait Tips
- Always follow label directions.
- If ground is dry, water area to be treated. Scatter bait directly from the container or use a hand-held spreader.
- Scatter granules in groundcovers and lawns, and on soil surface around plants. Do not put granules into piles.
- Do not apply to foliage or edible parts of plants.
- Sprinkle lightly with water after application.
Snails and slugs (University of California IPM)
By Lee Townsend, Extension Entomologist