Slugs and snails

Slugs and snails are predominantly pests in the southern and western regions. Snails are not a problem in the northern region, however dam­ag­ing slug pop­u­la­tions have been reported in seedling crops in north­ern NSW and south­ern Queens­land in recent years.

Increased slug and snail activ­ity may be due to the increase in zero/minimum till and stub­ble reten­tion prac­tices because the organic con­tent of pad­docks increases under such sys­tems, pro­vid­ing an increased food source espe­cially to young slugs and snails.

Other risk fac­tors include pro­longed wet weather, trash blan­kets, weedy fal­lows and a pre­vi­ous his­tory of slugs and snails. Slugs and snails are best con­trolled before the crop is planted.

Species Distinguishing features Characteristic damage Seasonal occurrence Other characteristics

Slugs

Grey field or reticulated slug Deroceras reticulatum

Grey field slug

Image: Michael Nash, SARDI

Light grey to fawn with dark brown mottling. 35 to 50 mm long. Produces a white mucus Rasping of leaves (complete areas of crop may be missing) Autumn to spring when conditions are moist especially when soil moisture greater than 25% Resident pest. Surface active, but seeks moist refuge in soil macro-pores.
Black keeled slug Milax gagates

black keeled slug

Image: Michael Nash, SARDI

Black or brown with a ridge continuing from its saddle all the way down its back to the tip of the tail. 40 to 60 mm long. Rasping of leaves (complete areas of crop may be missing), and hollowed out grains All year round  if conditions are moist, but generally later in the season in colder regions
  • Burrows so cereal/maize crops fail to emerge
  • Prefers sandy soil in high rainfall areas (>550 mm), heavier soils in low rainfall areas (<500 mm).
  • Surface active (feeding), but seeks moist refuge in soil macro-pores
Brown field slug Deroceras invadens or D. laeve

Brown field slug

Image: Michael Nash, SARDI

  • 25 to 35 mm long, and usually brown all over with no distinct  markings.
  • Produces a clear mucus
  • Rasping of leaves
  • Leaves a shredded appearance
All year round  if conditions are moist
  • Prefers warmer conditions and pastures.
  • Less damaging than grey field and black keeled slugs

Snails

Vineyard or common white snail Cernuella virgata

Vineyard or common white snail

Image: Michael Nash, SARDI

  • Coiled white shell with or without a brown band around the spiral.
  • Mature shell diameter between 12-20 mm.
  • Open, circular umbilicus*.
  • Under magnification regular straight scratches or etchings can be seen across the shell

 

Shredded leaves where populations are high.

Found up in the crop prior to harvest.

  • Active after autumn rainfall
  • Breeding occurs once conditions are moist (usually late autumn to spring).
  • Mainly a contaminant of grain.
  • Congregates on summer weeds and up off the ground on stubble.
White Italian snail Theba pisana

White italian snail

Image: Michael Nash, SARDI

  • Mature snails have coiled white shells with broken brown bands running around the spiral.
  • Some individuals lack the banding and are white.
  • Mature shell diameter between 12-20 mm.
  • Semi-circular or partly closed umbilicus*.
  • Under magnification cross hatched scratches can be seen on the shell.
Shredded leaves where populations are high.

Found up in the crop prior to harvest.

  • Active after autumn rainfall.
  • Breeding occurs once conditions are moist (usually late autumn to spring).
  • Mainly a contaminant of grain.
  • Congregates on summer weeds and up off the ground on stubble.
Conical or pointed snail Cochlicella acuta

Conical snail

Image: Michael Nash, SARDI

  • Fawn, grey or brown.
  • Mature snails have a shell length of up to 18 mm.
  • The ratio of the shell length to its diameter at the base is always greater than two.
Shredded leaves where populations are high.

Found up in the crop prior to harvest.

  • Active after autumn rainfall.
  • Breeding occurs once conditions are moist (usually winter to spring).
  • Mainly a contaminant of grain.
  • Can be found over summer on and in stubble and at the base of summer weeds.
Small pointed snail Prietocella barbara

Small pointed snail

Image: Michael Nash, SARDI

  • Fawn, grey or brown.
  • Mature shell size of 8-10 mm.
  • The ratio of its shell length to its diameter at the base is always two or less.
Shredded leaves where populations are high.

Found  up in the crop prior to harvest.

  • Active after autumn rainfall.
  • Breeding occurs once conditions are moist (usually winter to spring).
  • A contaminant of grain, especially hard to screen from canola grain as the same size.
  • Mainly found over summer at the base of summer weeds and stubble.
  • Similar to slugs will go into soil macropores.
  • Especially difficult to control with bait a current label rates.

*Umbilicus – a depression on the bottom (dorsal) side of the shell, where the whorls have moved apart as the snail has grown. The shape and the diameter of the umbilicus is usually a species-specific character.