There are many slug species across the United States, with a heavy concentration in the Pacific Northwest due to high levels of rain and humidity. Some of the most common include the gray garden slug, the banded slug, the tawny slug and the greenhouse slug1.
Since both slugs and snails are hermaphroditic, each one has the potential to spawn an all-out attack on a garden, laying eggs up to 6 times each year2. Eggs are laid during fall, hatching just prior to spring.
Slugs and snails prefer to feed on vegetation after sunset or prior to sunrise, preferably in cool, damp conditions. They can burrow into soil to find moisture during droughts. They secrete mucus while moving, leaving their well-known silvery trails behind as evidence. The shiny slime trails that crisscross home gardens are obvious signs of an infestation, and usually lead directly to plants riddled with holes.
A large slug or snail population can take over a garden and promptly eat through bedding plants and ornamentals. Plants with succulent foliage such as dahlias, hostas, geraniums, marigolds, roses and primroses are prime targets. Also, tomatoes, strawberries and artichokes are common favorites among both slugs and snails. Home gardeners should look for the characteristic slime trails and holes in flowers and vegetation.
Generally, a slug and snail population can be determined by geographic location. For instance, the Pacific Northwest (specifically Alaska, Washington and Oregon) is known to have a high slug density, especially compared to its minimal snail population. Conversely, it is very common to hear home gardeners in southern California complaining that snails are ravaging their rose gardens, with only a rare gripe about slug damage. While there are complaints about slug and snail problems throughout the rest of the county, the largest concentrations of infestations remain on the West coast.
Slugs and snails are active throughout the warmer months, emerging from hibernation during the first warmer days and not fully returning into hibernation until the first frost. During early spring, both mature and just-hatched slugs and snails thrive in a combination of mulch and constant irrigation. Newly planted summer annuals and bedding plants are especially likely targets.
In the Pacific Northwest, the first warm “false spring” days in February and March cause the emergence of slugs, preying on home gardens unprepared for the damage young slugs can do to their unprotected early plantings. Snails are generally active at this time as well in central and southern California, where there is less rain and humidity.
1http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7427.html
2http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7427.html
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