Manitoba Agriculture, Food and Rural Initiatives
Slugs I
Slug egg |
 Slug on straw |
Slug on strawberry |
 Slug damage to strawberry |
Host Plants and Distribution
Depending upon the location, there may be several species of slugs that cause problems. The most commonly reported slug in the literature is the grey garden slug, Deroceras reticulatum. In Manitoba, the primary pest is the grey field slug, Deroceras laeve. Slugs are found in virtually all areas of North America, preferring humid environments. Host plants include a variety of horticultural and ornamental plants, but slugs will be discussed here as they relate to strawberries.
Biology
Life histories vary depending upon the species. The two species of Deroceras mentioned above have a similar life cycle. Adult marsh slugs are abundant immediately after snow melt, but quickly become scarce. Eggs are laid on damp soil and organic matter during June and July. During picking time (late June – early July), both eggs and larvae are present. Slugs reach a length of about 15 mm in Manitoba and vary in colour from white to brown to grey. In other regions there may be considerable variation. Slugs are smooth bodied and generally leave a slime trail behind, along the path they have travelled.
Symptoms and Damage
Signs of infestation include split and shredded leaves, slime trails and presence of slugs on berries. Slugs are most problematic in wet years or heavily irrigated fields. Damage is caused in two ways: first, by direct feeding damage to berries and second, by contamination of feces and the slime trails, which are cosmetically unappealing. Damage attributed to slugs is difficult to estimate because of the interaction of other factors, including poor weather conditions, diseases and other pests.
Scouting Techniques
Slugs will hide during periods of hot dry weather and may be difficult to find. To inspect for slug eggs, look under the straw layer between rows. Eggs will be visible as small, round, translucent balls.
Economic Thresholds
No thresholds have been established for this pest. Most years in the Prairies are sufficiently hot and dry during the summer to keep slug populations in check. In wet years, or in fields under heavy irrigation, 50 slugs per m2 is considered to be a heavily infested field.
For further information, contact your GO representative.
