Monday, October 25, 2010

What do Beer and Slugs Have in Common? By Elaine Lockey

Hosta with Slug Damage

Beer and slugs is a partnership that gardeners have been promoting for ages. For some amazing reason, put out beer and slugs will come calling. Once they fall into the beer they won’t get back out - an effective and simple means to control what can be a very frustrating garden pest.

Beer in Lamium
A fellow gardener was having problems with something eating her hostas and lamium. In fact, the lamium was being destroyed and our best guess on the culprit was slugs due to the tell-tale sign of slime trails on the leaves and stems. We also found that smaller leaves were sometimes entirely consumed on the lamium. The hosta leaves had irregular chew holes on them. She happened to have some cheap tasteless beer in the fridge so we decided to donate it to science. I was somewhat skeptical of this practice because I had never tried it but was morbidly eager to check out the cups the next morning.

We put out 5 shallow cups, some plastic tubs, a saucer and some pans and filled them about 1 ½ ” deep with the beer although ¾-1” probably would have done the trick. It’s a rather dark practice to try to envision how deep the beer needs to be so that a slug will drown. I hoped that I wouldn’t end up having slug nightmares. The shallow cups were placed in amongst the plants. We placed them on the soil surface but ideally they should be sunk into the ground. The next morning all 5 had at least 1-2 slugs in them, with one having 4. We also found a lot of earwigs, pillbugs and spiders which made us sad; perhaps sinking the cups in the ground would reduce these casualties.

We changed out the beer and did this for the next week and each morning found more slugs. We later learned that you can usually use the same beer for several days. We couldn’t believe how many slugs there were over the next several days. It’s too soon to tell if the worst-off plants will recover and if this was enough to truly take care of the problem but it’s a hopeful sign.

Why do slugs like beer? They are attracted to the odor of fermenting materials. Sugar-water and yeast mixtures will also work (1t yeast to 3ozs water). When dealing with slug issues, you have to think like a slug. Okay, maybe that’s not wise, instead think scientifically about what a slug might like. An ideal slug world? It is one filled with all things moist. Slugs bodies are mostly water and are very susceptible to drying so they love organic mulches and lots of wet gardens.

Slugs and snails are both gastropods and the most obvious difference between the two is the lack of shell on the slug. These creatures are more closely related to clams and mussels than insects. Slugs are soft bodied, legless, generally brown or gray, with eye stalks and vary in size from ¼” to 2” or larger. Slugs have specialized mouthparts that use a rasping function to feed on delicate leaves and stems, leaving irregular holes in leaves. Their favorite food is young seedlings, especially those found in your vegetable garden! Later in the season they will feed on ripening fruits and veggies, especially fruits and vegetables with direct soil contact.

They feed mostly at night which is why you rarely see them but see their signs. During the day they hide under leaves, in soil cracks and other sheltered locations. Due to their love for humidity, using drip irrigation or only using overhead watering during the early morning to reduce night humidity can be effective practices. The use of nonorganic mulches and removing garden debris around plants can help as can providing more air movement by spacing out plants and using trellises.

What about natural predators doing the job? According to the University of Minnesota Extension, “There are many types of animals that feed on slugs, such as beetles (e.g. ground beetles, rove beetles, fireflies), toads, snakes, turtles, shrews, ducks, starlings and other birds. To maximize the effect of natural enemies, minimize the use of chemical pesticides. Reduce chemicals by spot treating small pest problems, using baits, and avoiding unnecessary pesticides applications.”
For other options on controlling slugs, go to CSU Extension’s Fact Sheet on Slugs:

Slug feeding on hosta (Courtesy University of Minnesota Extension)