On a recent trip to visit my son Derek in Monterey, California, we hiked among the giant redwood trees in Big Basin Redwoods State Park. It was a rainy day, which enhanced the overall experience. It also brought out a banana slug for us to see. Apparently everything there is giant because this slug was almost 10 inches long and bright yellow.
We may not have giant slugs, but slugs can be a garden pest here. A rainy spring like this one sometimes results in numerous slugs that cause heavy damage, especially on hosta. Phil Nixon, 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 dogs can be harmed if they eat them.If you are tired of fighting hosta slugs, you might consider trying other shade plants. To learn how view our Four Seasons Gardening webinar Beyond Hosta – Perennials for the Shade by Horticulture Educator Martha Smith. The program is presented live for live home viewing on May 2 at 1:30 p.m. and again on May 4 at 6:30 p.m. Following the session, a taped version is available on YouTube. Registration and YouTube information are found at http://web.extension.illinois.edu/hmrs/4seasons.