The Slug Patrol

by Arzeena Hamir


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Nature's recyclers, thieves, and pests, whatever you call them, slugs are a constant presence in any garden here on the West Coast. I have yet to go through one season without sacrificing some tender beans or baby lettuce greens to these voracious eaters. This year, however, I have some new tools with which to tackle these slimy suckers.

The best way to combat slugs is to understand their life cycle. Know thy enemy! Slugs themselves are made up mostly of water and will begin feeding as soon as soil temperatures rise above 40 F (5 C), emerging from the soil or from protected areas. Slugs prefer to forage at night or on dull days when temperatures drop and the garden is damp. Their gelatinous eggs, laid in clusters of 40-100, can be found in the soil, under rocks and even in outdoor pots. Learn to recognize them!

Cultural Methods of Control

There are many simple things you can do in the garden to decrease slug damage. Because slugs are made up of so much water, they are very susceptible to drying out. In the early spring, cultivate your soil to expose their eggs to drying air & predators. Try to keep your garden as dry as you can without damaging your plants. This can be achieved by using drip irrigation or soaker hoses rather than overhead sprinklers. In addition, if you mulch your garden, keep the mulch well back from the base of susceptible plants. Better yet, consider waiting until temperatures rise above 75 F before you apply your mulch. Slugs also love warm compost piles so if you can, keep your pile separated from the rest of your garden.

Hand picking

Hand picking is an extremely effective way of riding your garden of hundreds of slugs. For the squeamish, chopsticks, tongs, or even hat pins can be used to catch the offending pests. The best time to hunt for slugs is 2 hours after sunset so take a flashlight. Finish the slugs off in a bucket of soapy water.

Attract or Repel?

Most gardeners choose either of these methods to prevent slug damage in their gardens. Attracting slugs into baits or to trap crops and then discarding them is a popular system. On the other hand, preventing them from getting to your prized plants is also important. Here are the basic principles:

Baits

Slugs are attracted to chemicals given off by the fermentation process. The most popular bait has been beer. However, not all beers are created equal. In 1987, a study at Colorado State University Entomology Professor Whitney found that Kingsbury Malt Beverage, Michelob, and Budweiser attracted slugs far better than other brands.

The range of slug traps is only a few feet so you need to supply a few throughout your garden. Never sink the containers with their rims flush with the soil level or you run the risk of drowning ground beetles, important slug controllers. The rims should be 1" above the soil's surface.

In the last couple of years, a new product has been released into the market that is receiving rave reviews from organic gardeners. Baits made from iron phosphate have been found to decrease slug populations without harming birds, small pets or humans. Scientists are still not sure exactly how these elements affect slugs but figure that they inhibit the slug from feeding anymore. The baits are sold commercially under the name Sluggo and Es-car-go.

Trap crops

Certain plants seem to be favored by slugs and can be used to divert slugs from your prized plants. Particularly good trap crops include: green lettuce, cabbage, calendula, marigolds, comfrey leaves, zinnias and beans.

Barriers

Certain plants will also repel slugs. Ginger, garlic, mint, chives, red lettuce, red cabbage, sage, sunflower, fennel, foxglove, mint, chicory & endive seem to be less prone to slug attack. Plant them around the perimeter of your garden to keep them from infiltrating.

Aside from diverting slugs to where you want them, gardeners can also use certain barriers to keep slugs out of particular spots. A ring of abrasive material such as eggshells, sand, wood shavings, diatomaceous earth, hair or ash can be placed around susceptible plants. These materials do have to be kept dry, however, in order to work. After rains, top them up again. Cutting the tops and bottoms off of plastic containers and using them as a cylinder around young seedlings can construct a more permanent barrier.

One of the most effective barriers, however, seems to be copper tape, as it works wet or dry. When slugs and snails make contact with the copper, there is a toxic reaction, similar to an electric shock, which repels them. The minimum width for the copper barriers needs to be at least two inches; slug barriers sold in nurseries are often smaller and should be doubled or tripled when installed.

Slug Predators

Many natural predators will eat slugs. Providing a habitat for them will help build their populations so that you do less work in the long run. Slug predators include:

  • Ground beetles - Like to live under wooden boards during the day.

  • Frogs - They prefer damp sites & a quarter of their diet may comprises slugs.

  • Birds - blackbirds and thrushes, robins, starlings, rooks and crows, jays, ducks, sea gulls and owls will eat slugs

There are a number of tools that a gardener can use to combat slugs. Hand picking, traps, barriers, baits, & predators are just a few techniques. So, rather than shrugging off slug damage as inevitable, choose from the slug control menu and you'll be surprised by the results.


Arzeena Hamir is an agronomist and President of Terra Viva Organics. When she's not planting peas or picking zucchini, she answers questions about organic gardening at advice@tvorganics.com.

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