February 6, 2010

1 - Snails can be a problem even with reduced irrigation.

Yard and Garden - February 6, 2010


Late last gardening season we suddenly had a lot of brown snails. We picked them off and "drowned" them and were careful to not put any garden waste in our compost pile.

I understand that over-watering might well be the cause. Recently you wrote an article about efficient watering and recommended drip irrigation rather than spray. We have had spray but could probably convert to drip fairly easily. Would this be a good move? I realize that we cannot overwater again, but would drip, plus mulch further encourage snails?

- Mary P.


Snails can be a big problem once you have them. The problem increases when there is adequate water, but they can survive rather long periods without water. Minimized watering as appropriate for xeriscapes will help a little, but they will take advantage of every irrigation. You will just limit the habitat with adequate moisture when you use drip irrigation and irrigate infrequently. Yes, organic mulch will also be beneficial to the snails, but it will also be beneficial for the garden.

There are systems to help you convert from spray irrigation to drip irrigation. Each spray riser can be converted to provide 8 or more irrigation lines to plants. It is important to use a valve intended for low volume irrigation because spray irrigation provides water to the garden in gallons per minute while drip provides the water in gallons (or part of a gallon) per hour. Some valve systems used with automatic system timers cannot work properly with the low flow. This may mean changing valves if that is the type of valve you have.

You can also treat the snails to reduce their population. One common method is the use of "beer traps'. Beer traps are created by putting beer in a shallow dish buried to its rim so that snails and slugs can easily crawl in. Once into the trap, they drown and no longer eat your plants nor reproduce to make more plant eaters. There is a rather non-toxic snail bait made from iron phosphate. This has a low toxicity for pets and birds, but kills snails. It provides plant nutrients and must be reapplied after a rain. Other people use the "salt" method. Salt sprinkled on snails will dry them and kill them. Table salt is toxic to many plants, so some gardeners use ammonium sulfate fertilizer. This fertilizer salt is placed in a band around plants that prevents snails from crawling to the plants and thereby protects the plants. It is extremely soluble and dissolves in even a light rain, so must be replaced frequently. This can create a problem because the fertilizer salt can damage plants if the plants receive too much. Place the band fairly far from the plant and do not over-use this method. Finally, the most effective method is the use of metaldehyde baits. This material is extremely toxic to dogs, cats, birds, and to you. Use it carefully if you use it. If you find it necessary, create a "bait station" in which the material is covered with a heavy dish or bowl that keeps dogs, cats, birds, and other non-target organisms away, but allows snails and slugs into the station. Use a small rock or board to slightly prop-up one edge of the bowl so snails can enter. Place an old leaf of cabbage, lettuce, or other succulent vegetable under the bowl and place the bait on the vegetable. This increases the chances that the snails will travel to and eat the bait. When the cover is removed, be sure no bait remains exposed.

Finally, there are predatory snails that eat other snails, slugs, and their eggs. These decollate snails will help reduce the population of brown snails, but will not eliminate them. If you use predatory snails, do not use the toxic baits. These snails have been effective for me in Albuquerque, but I do not know how well they will do in colder parts of the state.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.

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