Q: I’ve noticed slime trails in my garden and the lower leaves of my flowers are full of holes. What is going on?
A: Gardeners aren’t complaining about the amount of rain we’ve received this summer, but it brought with it uninvited guests – slugs. More like an oyster than an insect, slugs are soft-bodied gastropods that resemble snails without shells.
These slimy creatures can wreak havoc in the garden, feeding on the leaves of many plants, flowers, vegetables and fruits. They have file-like mouthparts used to rasp and chew plant material. Evidence of slug damage is irregular-shaped holes in leaves, especially lower ones. Entire leaves may be eaten, so the best way to identify slug damage is silvery slime trails left on the ground around the plant. Slugs are creatures of the night, feeding and foraging when it is dark and cool. You’ll have a hard time finding them on a sunny day; they hide under decomposing debris or in soil cracks to avoid the sun and dehydration.
In the spring, rake up leaves and garden debris that provide places for slugs to hide and lay eggs. Large wood chip mulch is a preferred hiding place as are boards or flat materials in the garden. Water your garden in the morning so plants can dry out before slugs’ evening feeding time. Slugs like moist conditions, so keep air circulating in the garden by increasing plant spacing and removing debris. Remove lower leaves of susceptible plants and stake plants that can provide hiding places. Avoid organic mulches such as grass clippings and straw.
Because of their high water content, slugs dehydrate quickly in the hot sun, so during the day they seek out places to hide and stay cool. Put down damp newspapers or boards in the garden at night. In the morning, lift and check for slugs. You can kill any slugs you find by drowning them in a pan of soapy water.
Slugs are attracted to decomposing and rotting materials. They also like fermenting chemicals like the ones in beer. Sink a jar or can in the garden so the top is level with the ground and pour in a few inches of beer. The slugs are attracted to the smell, fall in and drown. These traps can remain effective for a couple of days, as long as there is liquid in the trap.
Slugs don’t like to crawl over abrasive materials. Spread diatomaceous earth (tiny fossilized skeletons) or wood ash around plants, but be aware that moisture reduces the effectiveness of the barriers. Copper sulfate and copper strips also repel slugs. Salt is toxic to slugs and regular table salt poured on a slug will kill it. The downside is excessive salt is damaging to plants as well.
Slug baits are pesticides known as molluscicides. Most other chemicals used to control insects do not affect slugs. Metaldehyde is the most commonly used pesticide. It is sold as granular bait (Bug-Geta, etc.) or gel (Deadline, etc.) Meta products are labeled for use around flower gardens and ornamental plants. They should not be used around vegetable or edible crops. Follow the directions on the label for effective slug removal.
For more information on slugs, check out Colorado State University Extension Fact Sheet 5.515 at www.ext.colostate.edu/pubs/insect/05515.html.
Contributed by Valerie Smith, Colorado Master Gardener. Photo courtesy of Colorado State University Extension. For answers to your horticultural questions, contact the Master Gardener Help Desk at 636.8921 or CSUmg2@elpasoco.com. Access fact sheets and seasonal information on the El Paso County Horticulture website http://elpasoco.colostate.edu/horticulture/.