Published on Wednesday, 30 November -0001 00:00
U of M Extension
Area homeowners are reporting slug damage in flower beds, hosta plantings and vegetable gardens. They use rasping mouthparts to scrape and chew jagged holes in the leaves of plants and if populations are high enough, may actually consume entire leaves. They have been reported to be especially destructive to strawberries, lettuce, peas, members of the cabbage family and hostas. Later in the season we may find them feeding on the fruit and leaves of tomatoes, peppers and vine crops as well as many ornamentals.
Slugs are soft-bodied animals and are often described as snails without a shell. They often remain unseen as they feed at night and hide in damp places during the day. They secrete a slimy mucous trail as they move which can be seen as a silvery trail on plant leaves and smooth objects. In our area, they overwinter as eggs under mulch, plant debris, boards or other objects. A thorough clean up of plant material, weeds and debris after fall frosts will help eliminate eggs. The eggs hatch when there is plenty of moisture present and the small slugs begin feeding immediately. Slug damage begins in the spring and continues to occur until the first frost. During periods of hot, dry weather in middle of summer, they may aestivate by burying themselves in the soil or in a cool, moist site until rain and cooler weather returns.
Control of slugs begins by making the environment less favorable for them to live and reproduce. Mulches are desirable, but keep them shallow, two to three inches will be sufficient to prevent weeds and maintain plant moisture without encouraging slugs. Avoid using large wood chips for mulch as they will provide hiding places for slugs. Do not mulch with fresh grass clippings as slugs will feed on decaying plant material. Water the garden only when necessary and then water in the morning so that the plants are dry by evening. Prune lower leaves off plants and stake large plants to eliminate hiding places for slugs and to increase air circulation to keep soil drier.
Slugs can be trapped by placing boards, moist newspaper, small carpet samples or even flowerpots around plants where slugs have been feeding and then in the morning check and remove all the slugs that have hidden under the trap. Slugs are attracted to fermenting food and can be trapped using a container with beer or a yeast mixture. Sink a small jar, can, yogurt cup, half of a plastic bottle or similar container so that the rim is even with the surface of the soil and pour some beer or a fermenting mixture into the container. The slugs are attracted to the smell and will fall in and drown.
Since slugs are not insects, they will not be controlled by spraying or dusting the plants with an insecticide. When populations are high and damage not tolerable, pesticides can be effective. There are baits available that contain iron phosphate which can be used around edible crops and do not pose a threat to birds and pets. Products containing iron phosphate include Bayer Advanced Dual Action Snail & Slug Killer Bait, Sluggo, Escar-Go, and Schultz Slug and Snail Bait. Any iron phosphate that is not consumed by the slugs adds nutrients to the soil. Slug baits containing metaldehyde are effective, but have some restrictions in that it is inactivated by water, cannot be used in the vegetable garden and can be toxic to pets.
Copper compounds like copper silicate and copper sulfate are effective as repellents, but do not kill the slugs. These products are usually mixed with water and sprayed on the plants. Do not use these compounds in combination with baits as the slugs will avoid the baits. Copper strips or tape can be an effective barrier to slugs but may have sharp edges and are most practical for small gardens or containers. Diatomaceous earth can also be effective as a barrier when applied around plants. Diatomaceous earth has sharp edges and is abrasive to the skin of the slugs. It is effective only when dry and must be reapplied after rain or watering. Because it is very fine and can be inhaled, it is wise to wear a dust mask when applying this product. Some gardeners have had success using oyster shells or sharp poultry grit around the plants.
Always read and follow the label statements and directions carefully when using any of these chemicals or products. The plant or a broader listing including the plant you are using the product on must be listed on the label.