Slug Management in Vegetables

Frequent rainfall and excessive soil moisture in the fall and early spring can bring some unusual problems for vegetable gardeners and farmers – slugs are one of them (pictures show slugs infesting cabbages in Central Alabama). Slug build-up is also favored by the presence of high organic matter in heavy (clay) soil; organic matter not serves as a food source but also provides shelter from the environment and natural predators.
slug on cabbage leaf
Slug on cabbages in central Alabama

While slugs are invertebrate animals with soft bodies, snails have a hard shell that covers most of the body. Attack from slugs seem to occur at various stages of vegetable crops with high intensity in the late stages of crops that can lead to direct feeding damage and crop contamination. Slugs are very common on brassica crops grown during cooler weather in Alabama and several slugs may hide inside the maturing crop. Many crops have zero tolerance for slug contamination which may lead to crop disaster. In recent years, we have experienced slug activity in cabbage fields along with the yellowmargined leaf beetles resulting in complex pest outbreaks. Literature suggests that female slugs lay eggs in soil in small batches in damp areas; immature stages seem to have a limited foraging distance with repeated feeding in certain areas over several days.

Slug monitoring:  Some publications suggest using upturned plastic pots baited with chicken feed or other cereal based food (including malted beverages) as a way of attracting slugs early in the season for general population assessment. Unfortunately, using a number of slug traps with baits is often a cumbersome process and producers often get surprised when slugs appear on the crop. BioCare Slug Trap is a commercial vegetable-extract based slug trap that may be sufficient to monitor or trap out slugs in small areas.

Cultural tactics:  Manage surface residues and till the soil when necessary to prevent slug buildup. Drain waterlogged areas in and around crop fields when possible, or use abrasive materials such as sand in wet areas not under crop production. Limit irrigation or overhead watering during weather with frequent rainfall – use a soil moisture meter or other devices to accurately determine crop irrigation needs. Since slugs seem to like certain crops (e.g., soft-leaf brassicas), crop rotation, early planting, and timely harvest may help reduce the overall population levels.

Natural enemies:  Ground-dwelling carabid beetles are aggressive predators of slugs, but not sufficient to provide control in the environmental conditions that favor slugs in the first place. Nemaslug, sold commercially by BASF in the Eurpoean market, is an organic control option that uses endoparasitic nematodes to destroy slugs.

Molluscicides: Slugs are not insects; so many insecticides do not provide control. Commercial snail and slug-control materials typically contain:

  • Iron phosphate (e.g., Sluggo by Montery, OMRI-certified; Bonide Slug Magic for Gardens),
  • Volatile oil blend (Monterey All Natural Snail & Slug Spray),
  • Diatomaceous earth with amorphous silica (Perma-Guard Crawling Insect Control)
  • Bait premix of iron phosphate and spinosad (Bug-N-Sluggo by Certis, Monterey Sluggo Plus)
  • Sulfur (Bug-Geta by Ortho)
  • Metaldehyde (Southern Ag Snail & Slug Bait, Deadline Mini-Pellets)
    slugs on cabbage - ayanava majumdar.JPG
    cabbages infested with slugs

     

    The drawbacks for some of the listed formulations is the high cost, low availability, and restricted crop uses. Multiple applications of products may also be needed for sustained effect. Always read the product label and/or consult the manufacturer before using molluscicides on high-value crops, since field research-data is very limited for many products. Check the OMRI symbol for organic farming use. Contact Alabama Extension Regional Extension Agent for correct pest identification and development of IPM plan.  

References:

Ayanava Majumdar,

Extension Entomologist & State SARE Program Coordinator