Dealing with slugs in your garden
Slugs can best be described as snails without shells. They are a type of mollusk, related to clams and oysters. Slugs are soft-bodied, generally brownish or grayish in color with their eyes on stalks. They vary in size from 1/4 inch to more than two inches. As they move, they secrete a silvery slime trail. Their mouth parts are file-like to rasp and chew plant tissue creating irregularly shaped holes. Feeding damage can be cosmetic; however, extensive feeding can result in plant stress or even death.
Slugs usually overwinter as eggs in protected sites on the ground, such as under plant debris, mulch, or boards. Eggs hatch during spring or early summer. Depending on conditions, slugs may lay eggs throughout the summer. Slugs are most active at night when it is cool and damp, although they may be seen during the day in cool, shaded sites. Warm, dry conditions are less favorable to them.
It is especially important when doing spring clean-up, to remove leaves and plant debris which may contain slug eggs. Also remove boards and other material to reduce favorable areas for slugs to hide. Avoid using large wood chips as they provide hiding places for slugs. Keep the mulch only three inches thick and pull the mulch back 5 to 6 inches from the base of each plant (this is especially important if it is a hosta plant, one of their favorites). This will protect the plants from weeds and help maintain plant moisture while minimizing a favorable environment for slugs.
Water your garden only when necessary. When you water, water in the morning and water only the base of the plant, not the leaves. This way the plant has more time to dry off by evening. Prune lower leaves or stake large plants to reduce potential hiding places for slugs and to allow better air circulation that helps keep the soil surface drier. Thin or divide plants if they are too crowded.
You can trap slugs by setting out several flat boards, shingles or damp newspapers. Check under these traps the next morning and kill any slugs that are hiding there. You can drown slugs in soapy water, crush them, or spray them with household ammonia diluted to a 5 to 10 percent solution.
Traps containing beer can be made by sinking jars, cans, pans or similar containers into the ground so the top is level with the ground. The container needs to be deep enough so the slugs fall in and drown. If it is shallow, they can crawl out. Pour beer or a water and yeast mixture (one teaspoon or yeast to three ounces of water) or similar fermenting liquid into the container. Slugs are attracted to the odors, fall in and drown.
Diatomaceous earth (tiny fossilized skeletons of ancient aquatic diatoms) is only moderately effective as a slug barrier. When slugs come in contact with diatomaceous earth, it is abrasive to their skin. Diatomaceous earth is most effective when used in dry conditions and has little effect when it absorbs moisture.
Iron phosphate (e.g. Escar-go, Sluggo), 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.
Chemical slug baits often contain metaldehyde (e.g. Deadline, Defender), available as a granular or liquid paste. When metaldehyde is eaten by slugs, it destroys their ability to move and digest food. Apply it to the soil near slug-infested plants. Metaldehyde is more effective during warm,dry weather. It is best to apply metaldehyde after a rain storm but when sunny weather is predicted.
Copper compounds (copper silicate and copper sulfate) are effective repellents. They are usually mixed with water and then sprayed on plants. Copper products repel slugs but do not usually kill them. Do not spray copper compounds near baits, as slugs will avoid baits contaminated with copper compounds.
Slugs are not supposed to like cocoa mulch (made from cocoa bean shells), however, this mulch contains a chemical called theobromine, which is an ingredient used to make all chocolate, especially bakers and dark chocolate. For this reason some people like to use cocoa mulch around plants like hostas. This mulch smells like chocolate and it attracts dogs and cats. It is toxic to them and maybe other pets, so be aware of this.
There are many types of animals that feed on slugs, such as beetles (e.g. ground beetles, rove beetles, fireflies), toads, salamanders, snakes, turtles, shrews, chickens, ducks, starlings and other birds. To maximize the effect of natural enemies, minimize the use of chemical pesticides.
Kyle Schulz is a Wadena County Master Gardener from Sebeka, and the regular gardening columnist for the Wadena Pioneer Journal.