An aggressive effort to eliminate slugs during the approaching fall season will produce amazing results come spring, especially for gardeners whom have had slug infested plants this growing season. Controlling your garden's slug population in the fall allows your plants, especially shade plants such as hostas, to begin their spring growth season free from unsightly holes in their leaves and in extreme cases total devastation of the entire plant. Effort now prevents a slug feeding frenzy come spring.
If you are not familiar with slugs they are "simply snails (mollusks) without shells." Ohio State University Extension Fact Sheet "Slugs & Their Management HYG-2010-95" by David J. Shetlar. "Slugs and Snails are classified as gastropods. They are more similar to clams and mussels than to other common pests such as insects." Colorado State University Cooperative Extension no 5.515 "Slugs" by W. S. Cranshaw. They come in a variety of colors including black, grey and covered in leopard spots. Grey and black slugs are most common in my part of the country (Midwest) however leopard spotted slugs can occasionally be found, adding a stylish element to garden destruction.
These slimy, ovalish creatures expand to a length of up to seven inches. A slug will normally appear much smaller when you spot it on the underside of leaves but if you catch it moving or you place it on your hand, it will expand up to and average length of around one to two inches. Slugs also have noticeable antenna when they elongate. Normally a gardener will find slugs in a nonelongated state where they appear to be wet black or grey lumps. Black slugs often have grey underbellies. Young slugs will often appear as black or grayish/ beige dots on plants and their surrounding garden beds. Young black slugs are almost impossible to spot unless they are on a plant of contrasting color. Black slugs often are mistaken for wet specks of dirt.
All slugs feed on a wide variety of ornamental plants and vegetables. They can consume young seedlings and maturing fruits and vegetables, damaging your crop at both the beginning and end of the growing season. See CSU Cooperative Extension no 5.515, "Slugs". The most common indicator of a slug problem is the appearance of holes in the middle of a plant's foliage. If a clear slime trail is also present on or around a plant, slugs are most likely the problem. Slug trails are most evident in early morning before dried by the sun. Slugs are nocturnal and feed mostly at night or early morning. They do not like light and hide during the day. The best time to look for evidence of slug infestation, (either the trails or the slug itself), is before the dew is dried by the sun. Slug trails can have a silver tint in the early morning and to assist in differentiating dew from slug trails just remember dew does not form a path to and from your favorite Hosta. Rain will bring these pests from their hiding places so any cloudy day after a rainstorm gives a gardener the opportunity to assess whether slugs are damaging their garden. Nighttime is also a very good time to check the garden but be prepared for strange looks from neighbors when you appear to be gardening by flashlight. Even neighbors who garden are often uneducated concerning the nature of gastropods and may ridicule your efforts. Presentation of a large slug often stops this reaction either because your neighbor is revolted by the slug or suddenly realizes your gardening knowledge is far superior to theirs.
The neighboring garden bed may also be the source for your infestation. A slug can travel further than most realize by utilizing slime trails, traversing over rougher terrain then most researchers give them credit for. I personally watched in amazement as a slug, utilizing a slime trail, traveled from one garden bed to another crossing a new textured concrete drive in the process. The slug was not injured though the concrete drive irritated my hands. Cypress mulch does not slow these creatures even though its rough edges should damage a slugs' body which consists mostly of water. Slugs will also escape yard waste containers if not properly sealed. Examining the lids of trash cans containing infested waste will frequently reveal a number of slugs trying to escape their containment. Excessive heat does seem to eliminate this problem as does topping your waste with salt or other slug pesticide. Before blaming your slug problem on your neighbor's garden it is first wise to correct the problem in your own garden and then begin to place barriers to prevent re-infestation.
Salt evaporates the water in a slug's body thus killing it. Salt, however, cannot be used directly in the garden since it will contaminate your soil and kill your plants. Chemical pesticides are available in most garden stores which claim to retard or kill slug populations. Gardeners with pets or small children are often reluctant to utilize these products in fear that they will harm more than the slug population. Dried egg shells, traps and containers of stale beer are all somewhat effective and detailed in most gardening manuals. An organic alternative to pesticides is the introduction of natural predators to control whatever gardening pest you are experiencing. The natural predators for snails and slugs are not attractive to the average gardener. Frogs eat slugs and if your garden is suitable to maintain a frog this may be a natural and picturesque method to reduce the slug population. Several types of birds eat slugs but I have not found them to be and adequate control method. The presence of a dog or a cat in a yard will reduce your bird population and therefore their effectiveness as a slug deterrent. A comprehensive list of slug predators can be found on the website, "Slug& Snail Trail" "www.haywardm.supanet.com/predators.html. The parasitic nematode, Phasmarhabditis hermaphrodita, is mentioned in this list as an effective slug predator. Links to suppliers of products containing these nematodes can be found on the above mentioned website.
If you are nervous about introducing biological agents into your garden or you are merely a frugal gardener, handpicking slugs and their eggs from your garden is the most effective first assault on a slug population. This method is environmentally safe and allows a gardener to assess the degree to which slugs have made your garden their home.
While many individuals are initially revolted by slugs, close observation of this creature inspires a rather begrudging admiration. While I have not yet made a slug my pet, as have individuals I know, I do have respect for their adaptation to their environment and their ability to survive. I view them as a worthy foe, not to be underestimated in my quest for a beautiful garden.
As previously noted, slugs have few natural predators in an average garden. The very elements that produce a beautiful, productive garden, good soil and moisture also produce healthy slugs. While dry weather reduces slug activity, it does not eliminate the problem. A good rainstorm or watering will bring the pests from their hiding places to begin again their assault on your garden.
A good freeze does not kill slugs as it does so many other garden pests. (Note some species do die in winter but not the grey or garden slug) Slugs over winter in your garden. This means slugs essentially hibernate during the winter months when plant life is scarce. During those brief warm spells that occur during winter, active slugs can be found under garden edgings and under leaf piles. In fact slug eggs are rather easy to find during the winter months if you can differentiate them from ice crystals. Slug eggs, tiny crystal-like balls, can be found in groupings of five to thirty, beneath the mulch, dirt, and in cracks and crevices of a garden. These eggs can be found in the garden during the entire year but sense slugs lay their eggs primarily in the fall and in the spring, finding the eggs in the winter is not unusual. These eggs survive the winter and will bring a new crop of slugs come spring.
The mating season for slugs is August to mid-October. There is some evidence slugs can reproduce asexually but most slugs seem to seek a mate. Within a few days after mating, the slug lays eggs into a hole in the ground. See Wikipedia, the free encyclopedia. In warm weather these eggs can mature in as few as ten days. Efforts in the fall to eliminate slugs from the garden can not only eliminate fertile slugs that will lay eggs in the spring, eggs laid in the fall ,young slugs can be stopped from over wintering and destroying seedlings and emerging plants in the spring.
Once slugs are identified as the culprit the severity of the problem should be assessed. If a cursory inspection of the garden reveals numerous mature slugs of considerable size and even slug resistant plants are showing signs of slug damage a severe problem is present. Minimal plant damage, no visible slug trails nor mature slugs indicates a minor problem that pesticides or egg shells should correct.
When infestation is severe, drastic action should be taken. All plant debris and mulch should be removed from the affected area. Mulch provides a moist environment that slugs need to survive. Mulch also provides excellent hiding places for slugs and their eggs, making detection and removal extremely difficult. Mulch should be removed and the garden bed should not be re-mulched for at least a year. All yard waste, including mulch, should be disposed of, not composted for home use. If you compost this material you are merely relocating your slug population, not eliminating it.
The most severely damaged plants should be cut to the ground. Annuals should be removed first. Fall is the time annuals are removed from the garden so their absence in fall is not as ascetically unpleasing as removal would be during the rest of the growing season. Check the holes left by the removal of annuals for slugs and their eggs. Remove any signs of infestation. Cut the majority of the perennials to the ground, leaving some plants to serve as bait for the slug population. Dispose of the plant waste. Inspect the remainder of the plants for signs of infestation, not forgetting the remainder of any perennial you have cut to the ground. For seriously motivated gardeners, perennials can be dug up, inspected and replanted if eggs or slugs are not found in the root system or they have been removed. Throughout the fall continue to inspect your garden for indications of slug infestation and utilizing a hand rake or garden claw disturb the garden dirt so as to uncover and disrupt any slug hiding places or eggs. Keep the garden beds free of leaves and other garden waste since slugs are not only attracted to live plants but also to decaying garden matter. After the first freeze, cut the rest of your perennials to the ground.
Finally, check under material used as edging, such as bricks, stones or plastic. If the edging is permanent, utilizing a stick or garden tool, disrupt the ground by creating an indentation in the dirt on both sides of the edging material to discover eggs and active slugs. If your edging is movable, periodically turn your bricks or stones over and inspect them and the ground beneath for evidence of infestation. Garden ornamentation such as small statues, baskets, or flower pots should be checked regularly for live slugs as these ornaments serve as perfect hiding places for garden pests.
Finally prevent slugs from re entering your garden. Slugs will often hide in your lawn. During a particularly sluggy summer, slugs can be seen atop a lawn early in the morning or after a rainstorm. Slugs have also been observed dropping from trees, disturbing more than one early morning paperboy. Most garden books suggest copper striping as an effective slug barrier. Diatomaceous earth and lime are also mentioned. Only the copper striping does not need to be replaced after rain. Copper striping may be effective, but utilizing copper plumbing pipe was not effective in my experience. Dried crushed egg shells appear to have some effect as their edges become razor sharp and theoretically cut the slug causing death. Egg shells must be replaced when it rains but hopefully they add calcium to the soil. If there is evidence that your infestation is coming from either your lawn or adjoining gardens, daily sprinkling of dried egg shells, or any other barrier method is worth a try.
The most common suggestion for disposing of live slugs is to drop them in a bucket of soapy water where they drown. If lugging a bucket of watery dead slugs does not appeal to you , I have found placing them in paper yard waste bags which then must be tightly closed, will also work. A light dusting of salt on the top will ensure that any escapees will be stopped in their tracks. Placing the slugs in plastic bags used to pick up animal waste and disposing of them will also insure your garden pests will not return to their old chomping grounds.
If your slug problem is less severe, or you are obsessed by the need for a perfect garden, inspection in the fall will help you prevent (or at least slow) any slug problems in the spring. Each slug you remove is one more slug that cannot mate, reproduce, or over winter in the garden. Removing leaves, dead foliage, and annuals will go a long way to keeping your garden pest free. The garden will lose the important nutrients that homemade mulch can provide, but most leaves and annuals are removed in spring anyways. Perennials will survive the winter without protection and will look better in the spring if beds are cleaned in the fall. Rotating years when you utilize plant foliage and shredded leaves as additives to your garden is a prudent course of action when only minor slug infestation is present.
Handpicking slugs is dirty, slimy work. The results, especially if started in the fall and continued in the spring, will be a beautiful pest free garden. (Well almost). By getting down and dirty, a gardener becomes in tune to the garden habitat including garden pests and their lifecycles. Problems become easier to identify, thus can be corrected earlier before serious damage is done. Slugs are well adapted to thrive in the average garden. Interrupting their habitat and habits is the most effective way of controlling their population. While winter slug hunting is a little extreme, it may give a bored gardener something to do on a warm February day. Fall slug control; however, is a must for all gardeners who want beautiful plants come spring.