While hiking at Turkey Run State Park with friends recently, we found a lot of snails sitting on stinging nettle leaves along the trails. Many of the snails had their head and antennae out of their shell, inviting us to stop occasionally to say hello.
We also noticed a lot of holes in leaves along the trails. There are probably numerous reasons for the damage, but slugs are a likely culprit. Slugs can be a severe garden pest, especially during rainy periods. A rainy spring sometimes results in numerous slugs that cause heavy damage, especially on hosta. Phil Nixon, retired Extension Entomologist, offers for following information about slugs.
Slugs, which are shell-less snails, are usually a problem on thin-leaved plants growing in shady areas--hosta, violets, and impatiens. Following a spring with prolonged, heavy rainfall, slugs are often also numerous in sunnier areas, feeding on a wide range of plants.
The most common species is the gray garden slug, which is usually about 3/4 inch long but may be up to 1-1/2 inches long. Slugs have two pairs of tentacles extending from the front end of the body. The upper, longer pair are optic tentacles with eyes on the tips. There is also a shorter pair near the ground that is sensory tentacles for feeling and smelling. The largest structure is the foot, which runs the length of the slug. The underside of the foot is called the sole.
Slugs feed with tiny teeth that scrape away a leaf's surface and then the plant material underneath. This feeding mechanism causes damage to appear most commonly as holes in the leaf. On some plants or in large numbers, slugs will eat the leaf margins. You can verify that slugs are responsible by checking for their presence at night or on foggy mornings. Slime trails might also be visible in the morning when they reflect the sunlight before drying up.
Slugs need a moist environment to survive, and they feed on decaying organic matter. The best long-term control involves reducing this supply. Under less rainy conditions, spacing plants farther apart or pruning them back allow better air circulation and creates drier conditions that are difficult for slugs. Eliminating fallen leaves, bark mulch, and other dead organic material will reduce slug numbers by reducing food sources.
Baits are used to attract snails and slugs into traps where they then drown. One popular type of bait is beer. Pour beer into a shallow pan and sink it into the ground with the pan edges sticking up 1/8 to 1/4 inch. Snails and slugs are attracted to the yeasty smell of beer, and they fall into the pan and drown. Commercial poison baits are also available. Read labels carefully and be careful because baits can harm dogs if eaten.
By the way, if you are a hosta lover, consider joining a local hosta society. The Central Illinois Hosta Society hosts events and tours throughout the year. The Midwest Regional Hosta Society's 2018 convention was in E. Peoria this week. Learn more about both at http://www.cihshostaclub.org.