Slugs are terrestrial mollusks that play a role as decomposers in the garden ecosystem, breaking down decaying plant material. Despite this beneficial function, their tendency to consume young seedlings and tender foliage often positions them as significant garden pests. This article provides practical guidance for gardeners seeking to manage slug populations and minimize plant damage.
Understanding Slug Biology and Environment
Slugs are largely composed of water and are extremely susceptible to desiccation, which dictates their constant need for moisture. They survive by secreting a protective layer of mucus, which facilitates movement and helps prevent them from drying out. This dependence on high humidity means they are most active following rainfall or during the cool, damp conditions of the nighttime.
Ideal slug habitat is characterized by damp, dark hiding places that offer shelter during the dry daylight hours. These refuges often include dense ground cover, piles of stones or debris, un-tilled soil with cracks and crevices, and the underside of planters. Slugs are hermaphrodites, meaning each individual possesses both male and female reproductive organs, and any slug can potentially lay eggs. They lay hundreds of eggs per year in clusters in moist, sheltered soil, leading to rapid population growth.
Non-Lethal Methods for Coexistence
Environmental modification is a primary strategy for reducing slug activity without resorting to lethal means. Adjusting the garden watering schedule to water in the morning instead of the evening allows the soil surface to dry out before nightfall, making the environment less hospitable for nocturnal slug foraging. Improving soil drainage and removing potential daytime shelters, such as excess mulch, fallen leaves, and wooden debris, eliminates their preferred resting spots.
Physical barriers can deter slugs from reaching vulnerable plants. Copper tape, when wrapped around the rims of pots or raised beds, creates a mild electrical charge when the slug’s slime reacts with the metal, which deters them from crossing. While often recommended, materials like crushed eggshells or diatomaceous earth are not always effective barriers, as slugs can often traverse these sharp or abrasive surfaces by secreting extra slime.
Handpicking and trapping are direct physical management methods. Slugs can be easily collected at night with a flashlight or by checking under temporary traps like a damp piece of cardboard or wood. A simple beer trap, consisting of a shallow container sunk into the ground and filled with a fermented liquid like beer or a yeast-water mixture, attracts slugs with its scent. While many slugs take a drink and leave, some will fall in and drown, providing a localized reduction in the population.
Intervention Strategies for High-Volume Problems
When non-lethal methods are insufficient to control a high-volume infestation, targeted intervention strategies may be necessary. Iron phosphate baits are a common choice, as they are a safer alternative to older metaldehyde pellets. When ingested, iron phosphate disrupts the slug’s digestive tissue, causing them to stop feeding and eventually die.
It is important to note that many iron phosphate products contain a chelating agent, often EDTA, which enhances iron uptake in the slug. This may also increase the risk of toxicity to non-target organisms like earthworms, dogs, and other wildlife if consumed in large quantities. Gardeners should use these baits sparingly and always follow label directions to mitigate risks.
Biological controls offer a highly specific method of population reduction. The nematode Phasmarhabditis hermaphrodita is a microscopic, parasitic worm commercially available for slug control. These nematodes are applied to the soil where they actively seek out and enter the slug’s body, releasing symbiotic bacteria that stop the slug from feeding and ultimately lead to its death within a week or more. This biological agent is safe for mammals, birds, and insects, as it only targets mollusks.