Sunflowers (Helianthus spp.) are annual and perennial flowering plants that are simple to grow and attract beneficial pollinators to a garden. Many varieties of sunflowers grow in all U.S. Department of Agriculture (USDA) plant hardiness zones, but not all perennial sunflowers are hardy in all USDA zones. A variety named perennial sunflower (Helianthus multiflorus "Flore-pleno"), for example, is hardy in USDA zones 4 to 10. Although sunflowers require little care and can perform double-duty as decorative flowers and bird feeders, they are a favorite food of slugs. Slugs reproduce quickly and create significant flower damage. Certain control methods, however, can prevent slugs from decimating sunflowers.
Although you might spot the slimy mollusks during the day, slugs are nocturnal creatures that tend to cause the bulk of their damage at night. Many colors and species of slugs exist. The most common type is the 3/4-inch long gray garden slug (Deroceras reticulatum), which range in color from pale yellow to black with brown spots. Slugs are male, female or hermaphrodite; the latter can fertilize itself. A single slug lays up to 500 eggs in its lifetime. The eggs hatch in spring and early summer. Slugs perform the most damage during late summer and fall but also feed on tender plant seedlings, which makes young sunflowers vulnerable to slugs.
Commercial Slug Baits
Commercial slug baits are available but often contain metaldehyde, which is toxic to children, dogs and cats. Also, the baits are not effective when used as the sole preventative method, and rain and sunlight decrease their chemicals' effectiveness. Alternative slug prevention methods, however, do not involve the use of harsh chemicals.
Soil Preparation and Watering Method
Before planting sunflowers, till the garden bed to destroy slug eggs that may be in the soil. Remove all debris, such as logs, leaves and stones, that provides hiding places for slugs, and plant sunflowers in areas that are away from slugs' usual hiding places. Consider using a drip-irrigation system instead of a sprinkler to water the plants; a drip-irrigation system decreases the humidity that attracts slugs. Place sunflowers near strong-scented herbs, which deter slugs.
Removal by Hand
Although handpicking slugs is not for the squeamish, it has the most effective results. Water plants in late afternoon to attract slugs, and handpick the slugs at night while wearing rubber gloves and using a flashlight to see the slugs. Place the slugs in a bowl with dish soap and water, which kills them, so they can be disposed of in a compost pile. Handpick slugs for three or four nights. Once the slug population has decreased significantly, do the task weekly.
Traps and Barriers
Place 1-by-12-by-15-inch wooden boards, flowerpots or upside-down melon rinds near sunflower plants. Slugs will congregate beneath those surfaces, where you can regularly collect and remove the slugs or crush them into the soil.
Copper deters slugs because it reacts with their slime, delivering an electrical shock to the creatures. Copper flashing or copper foil placed along the perimeter of sunflower plants provides protection against slugs for several years. Ensure the area you will surround with copper is free of slugs before adding the copper barriers.
Slugs and snails are attracted to beer. Place shallow bowls or cups of stale beer just below ground level with their tops above ground. Slugs will fall into and drown in the containers. Replace the beer every three days.
- Alternative Field Crops Manual; University of Wisconsin Cooperative Extension et al.
- University of California Integrated Pest Management Online: Snails and Slugs Management Guidelines
- Alabama Cooperative Extension System: Insect Pest Management in the Home Vegetable Garden
- Washington State University, Clark County Extension: Perennial Sunflower
- Photo Credit Shunsuke Yamamoto Photography/Digital Vision/Getty Images