Slugs and Snails

Classification and Description:  Slugs and snails are not insects, but rather gastropods.  Snails can be distinguished from slugs by the presence of a shell.  Several species of slugs and snails can occasionally be found in cotton fields.  Many of the snails found in cotton are detritivores and normally do not feed on plants. 

Hosts, Life History, and Distribution:  Plant feeding slugs and snails generally have a wide host range, and most species are widely distributed throughout Tennessee.  Slugs feed primarily at night.  They overwinter as eggs or "larvae".  Slugs may be seen early in the morning, especially on cool and cloudy days.  Reflective slug trails can sometimes be seen on plants with the help of the morning sun.  Once the sunshine hits, slugs head for cover.  During midday, slugs may be found 1-inch deep, under plant debris or in cracks or crevices.

Pest Status and Injury:   Even though snails can sometimes be present in large numbers, they rarely if ever cause economic injury to cotton.  In contrast, many slugs (e.g., marsh slug) will feed on cotton and other crops.  Slugs feed by making irregularly-shaped holes, normally along the leaf margins.  Severe feeding may result in "cut plants" reminiscent to that caused by cutworms.  Heavy infestations are uncommon but can cause significant stand loss.

Slug injury is primarily an early-season phenomenon.  Good growing conditions and dry weather help to alleviate potential damage.  Both slug and snail populations tend to be much higher in no-till fields.  Recent history suggests that most severe slug infestations are found in fields rotated from corn or sorghum.  Slug damage also tends to be greater in low areas of fields.  The worst damage seems to be in fields, or parts of fields, where the seed furrow did not completely close because of wet conditions at planting.  This essentially creates a slug "highway" that concentrates their activity in the row.

Management Considerations and Thresholds:  Unfortunately, there are not any insecticides that provide satisfactory control of slug infestation.  Metaldehyde is the active ingredient used in baits (e.g., Deadline MP) for control of snails and slugs, but these baits may not be economically feasible or readily available for field-scale applications.  Some literature indicates that the application of fertilizer, essentially "salting" the slugs, may suppress infestations.  Data from the Midwest suggests that "aggressive" row cleaners, which keep the seed furrow relatively clean of debris, will also reduce slug injury to the emerging crop.  If baits, insecticides or fertilizer are used for slug control, applications late in the day or even at night may increase the chances of success.

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