Slugs and snails - IPM Guidelines For Grains

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 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 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 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 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 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 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 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.