Controlling Garden Snails and Slugs - May 9, 2001
Jeff Schalau, County Director, Agent, Agriculture & Natural Resources
Arizona Cooperative Extension, Yavapai County
Snails and slugs are a common garden nuisance. They usually damage the leaves and stems of young, tender, herbaceous plants, but can also damage fruit, and tender bark of young trees. They especially like strawberries and tomatoes. Snails also feed on decaying vegetation, cardboard, and waste paper. Both are mollusks making them distant relative of clams and oysters.
In the Verde Valley, you may encounter two types of snails: the decollate snail and the brown garden snail. Decollate snails (Rumina decollata) are predators of juvenile garden snails. Even though they are beneficial predators, you should also be aware they eat seedlings, small plants, and flowers. In California, they have been introduced to control the brown garden snail (Helix aspersa) in several counties.
The brown garden snail can be a very serious garden pest when they become established. This is because mature snails have both male and female sex organs. After they mate, each of the snails will lay a clutch of about 80 eggs. The eggs are small (1/8 to 1/4 inch) and a pearly white color. Each adult snail can lay up to six clutches of eggs per year. Slugs follow a similar pattern, but mature at one year of age.
You may not see them because they are nocturnal. However, snail and slug damage is usually easy to identify because they leave a nice slimy trail. On cool moist days, you may notice them out in the daytime. They prefer dark, moist to hide on sunny days and are generally most active during the growing season. In really hot weather, snails have the ability to seal themselves off with a parchment like membrane to minimize moisture loss. Under these conditions, you may find them attached to trees or walls.
There are several methods of control and, like most things, there are tradeoffs associated with each. The best control results when two or more methods are used. Hand picking works for very sparse populations. Start handpicking in the daytime, to reduce the population, then get the flashlight and visit the garden at night. Captured snails can simply be placed in a ziplock-type bag and discarded, drowned in soapy water and composted, or stomped on the ground with sadistic pleasure. Salt is not recommended because it will raise salinity of the soil.
Traps are also easy to use. You can build your own by nailing 1-inch strips crosswise to an 18-24 inch long piece of 1x6. The place it on the ground with the strip side down to allow snails and slugs to crawl underneath it to hide during the day. Check it each morning and scrape and discard them. Beer (not bear) traps can also be used. To make a beer trap, pour cheap beer into a shallow dish in the evening. Fresh beer should be used, as it is more attractive than flat beer. Discard the drowned snails the following morning. This is possibly the most humane method of control, but it is really not effective for distances of more than a couple of feet.
Barriers can also be used. Copper barriers are somewhat effective because it is thought that their slime causes a flow of electricity, which repels them. I have also heard of gluing pennies to the outside of pots and concrete. Bordeaux mixture (copper sulfate and hydrated lime) can also be mixed and painted onto surfaces. One treatment is supposed to last for about a year. Some types of tanglefoot are also effective.
Aside from the decollate snail, there are many other natural predators of snails and slugs. These include toads, snakes, ground beetles, turtles, and domestic fowl (especially geese and ducks).
Baits containing metaldehyde or carbaryl can be hazardous to non-target organisms, such as dogs, cats, and children. If you use these products, assess the risks and place the bait in bait traps. I have a vivid childhood memory of watching my neighbor's Irish setter die after accidentally ingesting snail bait. It was not a pretty sight. Consequently, I do will not use them.
Newer molluscicides contain iron phosphate. These are safer around pets and wildlife. Iron phosphate does not kill instantly, but it causes the snails and slugs to stop feeding and they eventually die. As with any pesticide, always read the label and follow the directions. Remember to use more than one method if you want to be most effective.The University of Arizona Cooperative Extension has publications and information on horticulture and pest management. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at firstname.lastname@example.org and be sure to include your address and phone number. Find past Backyard Gardener columns or send me column ideas at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/.
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Last Updated: March 15, 2001
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