Garden Q&A: Slugs harmful but easy to control
Question: My problem is slugs. You can see where they have been from the slime they leave crossing my patio and up the sides of my brick house. What can I do about them besides inviting toads and snakes onto my porch? Thanks. I need help.
Answer: North America is home to nearly a thousand species of slugs and snails. These terrestrial mollusks are close relatives of octopi and clams, and they glide around the garden on a layer of protective mucus. Slugs are far more common in Pennsylvania than snails, and they can do quite a bit of damage to garden plants. Their mouths consist of an opening lined with tiny teeth capable of shredding holes into leaves.
Most slugs are decomposers, feeding largely on decaying plant materials, waste and fungi. But some species feed on the fruits and leaves of living plants, making them problematic for farmers and gardeners. It's interesting to note that nearly all of the slug and snail species considered to be agricultural pests here in North America are not native species. Most have been introduced from Europe since the 1800s.
Slugs can destroy tender seedlings, chew through strawberries and make holes in everything from cabbage leaves to hostas. Because they are prone to desiccation, slugs are most problematic during rainy seasons. They feed largely at night and on cloudy days, when they are protected from the drying sun. During the day, you'll find them hiding under mulch, rocks, plant debris and in other moist, dark places.
The two most common slug species here in Pennsylvania are the gray garden slug, a European introduction that is about 1 inch long and ranges in color from creamy coffee color to mottled gray, and the spotted garden (or leopard) slug. This European native reaches between 3 and 7 inches in length at maturity and is gray with dark, leopard-like splotches.
Spotting slime trails is often the first sign of a problem. Holey foliage is the second. Thankfully, there are several successful control measures you can readily employ that can significantly reduce slug populations.
• Plant resistant plants. Slugs and snails find heavily fragranced foliage distasteful. Plants such as lavender, oregano, sage and other herbs are mostly left alone, as are plants with fuzzy or stiff foliage.
• Trap slugs by laying two-by-fours between crop rows. In the afternoon, when slugs readily take shelter beneath them, simply flip over the board and dispose of the slugs. They also are easily trapped underneath inverted melon rinds scattered throughout the garden.
• Switch to drip irrigation, which keeps foliage drier than overhead irrigation techniques. And water only in the morning so foliage has time to dry before nightfall.
• Surround susceptible plants with a ring of copper foil or strips. Snail and slug slime reacts with the copper, causing a mild shocking sensation and acting as a significant deterrent.
• Sprinkle iron phosphate-based slug baits around the garden. These baits can be used around edibles and will not harm domestic animals or humans (unlike metaldyhyde or methiocarb-based baits, which should be completely avoided).
• Beneficial nematodes (species Phasmarhabditis hermaphrodita) can be added to water and distributed around susceptible plants. These microscopic roundworms seek out land mollusks and enter through their breathing pore, eventually causing death.
• While the commonly touted control method of sprinkling salt on slugs may work, it should be avoided. The salt can burn plant foliage and affect soil salinity and soil microbes.
• Beer traps will work, as the slugs are attracted to the fermenting yeast. But they will need to be emptied daily.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. Her website is www.jessicawalliser.com.
Send your gardening or landscaping questions to tribliving@tribweb.com or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.
