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Species Page

common garden snail

Cornu aspersum
This information is part of a full datasheet available in the Crop Protection Compendium (CPC). Find out more information on how to access the CPC.
©CAB International. Published under a CC-BY-NC-SA 4.0 licence.

Distribution

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Extent
Invasive
Origin
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Host plants / species affected

Main hosts

show all species affected
Actinidia chinensis (Chinese gooseberry)
Allium cepa (onion)
Beta vulgaris (beetroot)
Brassica oleracea var. capitata (cabbage)
Brassica sp.
Capsicum (peppers)
Citrus
Fragaria ananassa (strawberry)
Lactuca sativa (lettuce)
Persea americana (avocado)
Phaseolus vulgaris (common bean)
Polyphagous (polyphagous)
Prunus armeniaca (apricot)
Pyrus communis (European pear)
Ribes nigrum (blackcurrant)
Solanum lycopersicum (tomato)
Zea mays (maize)

List of symptoms / signs

Fruit - discoloration
Fruit - extensive mould
Fruit - external feeding
Fruit - lesions: scab or pitting
Growing point - external feeding
Growing point - lesions
Inflorescence - external feeding
Inflorescence - lesions; flecking; streaks (not Poaceae)
Leaves - external feeding
Leaves - rot
Roots - external feeding
Stems - external feeding
Stems - gummosis or resinosis
Vegetative organs - external feeding
Whole plant - external feeding

Symptoms

C. aspersum causes extensive damage in orchards (creating holes in fruit and leaves) and to vegetable crops, garden flowers and cereals.

In California, USA, populations established in citrus groves feed essentially on the foliage of young citrus and also on ripe fruits, creating small holes allowing the entry of fungi and decay of the fruit (see Pictures). Larger holes result in fruit dropping from the tree or being rejected for consumption during sorting and packing (Reuther et al., 1989; Sakovich, 2002).

In South African viticultural regions, C. aspersum feeds essentially on the developing foliar buds and young leaves of the vines. In kiwifruit vineyards (California, New Zealand), damage occurs on the flowers, not the fully developed fruit, since snails consume only the sepal tissue around the receptacle area. Damage to the sepals can be detrimental by increasing the development of the fungus Botrytis cinerea during cold storage of fruits, and moreover, the slime trail mucus stimulates germination of B. cinerea conidia (Michailides and Elmer, 2000).

Prevention and control

Prevention

SPS Measures

The Canadian Food Inspection Agency (CFIA, 2014) considers C. aspersum to be a plant pest and have quarantines established for preventing the importation of the snail in plant and soil matter. The United States Department of Agriculture requires a permit to import snails (or slugs) into the USA and between states within the USA from APHIS, Animal Plant Health and Inspection Service (APHIS, 2002).

Public Awareness

APHIS (2009) encourages people using C. aspersum in classrooms, nature facilities, or keeping them as pets to turn them in voluntarily. Some US states have created an ‘invasive species hotline' (e.g. Oregon, Hawaii, Michigan) for early detection of potential pest invaders. Residents of the state of Hawaii are asked to be on the lookout for this pest and to call a resident agricultural specialist on their respective island if they see this snail. It is currently recorded on only two of the Hawaiian Islands (Cowie, 1997; Cowie et al., 2008)

Containment/Zoning

In the USA, APHIS has produced containment guidelines to assist a researcher, educator, or commercial entity to design, build, maintain and operate a facility for rearing nonindigenous snails in the USA, including C. aspersum (APHIS, 2002), the non-respect of which is subject to civil and/or criminal penalties and loss of permits.

Control

Physical/Mechanical and Cultural Control

Handpicking with subsequent destruction of animals is the oldest method of control of pest molluscs. Even though it is time intensive, it can be effective as C. aspersum is gregarious and can be found in huge numbers under snail traps. Other places around susceptible plants where snails can hide during daily or seasonal dormancy, such as boards, debris and dense cover such as ivy, branches growing near the ground, stones, must be removed (Barker and Watts, 2002; Dreistadt et al., 2004).

Physical barriers such as continuous lines of wood ash, sand or diatomaceous earth can be effective for short-term control but their effectiveness is drastically reduced once they become wet (Davis et al., 2004; Dreistadt et al., 2004). Lines of lime and copper sulphate or copper screen are repellent to snails and can be used to prevent movement into an area. Various other organic and inorganic substances have been used as barriers to prevent snails getting access to plants. These barriers have proved to be moderately successful, and their effectiveness is greatly improved as part of an IPM approach along with pit-fall traps and hand collecting.

Containers filled with beer attract slugs and snails, but beer must be replaced regularly to be effective.

Bordeaux mixture (a copper sulphate and hydrated lime mixture) can be brushed on tree trunks to repel snails, one treatment should last about a year (Dreistadt et al., 2004). Thin copper sheets can also be wrapped around tree trunks to prevent snails from climbing into the canopy (Davis et al., 2004; Dreistadt et al., 2004). Du Toit and Brink (1993) tested treatments for the control of C. aspersum in citrus trees in South Africa, including chemical control using copper sulphate, metaldehyde and copper oxychloride, but the only treatment that reduced snails to an average of less than two per tree after 29 weeks was a copper strip around the stem preventing snails from climbing up it. The strips were 0.127 mm thick and 50 mm wide, and were fastened 500 mm from the ground with a paper-clip. They were still effective 12 months after application, and are recommended as a long-term control method. Removal of the lower branches of trees by pruning can minimize the contact of the foliage with the ground and help to reduce the number of C. aspersum on the trees. In California, skirt-pruning associated with copper sheets on the trunk and handpicking of snails stopped by this barrier can be very effective (Sakovich, 2002); and although no longer practised, running cultivation equipment through an orchard several times a year contributed to control of C. aspersum through destruction of buried egg clutches and snails buried in the ground (Sakovich, 2002).

Biological Control

As terrestrial molluscs have many natural enemies, there has been strong interest in the biological control of C. aspersum using other, predatory snails (e.g. Fisher and Orth, 1985). However, as most of these predatory snails are not host-specific, they are not appropriate to use in control programmes in which effects on non-target species are of concern (Cowie, 2001: Barker and Watts, 2002).

There have been several attempts to develop biological control of C. aspersum in California, South Africa and New Zealand, which began with the introduction of predaceous snails (Euglandina roseaGonaxis sp.) and beetles during the 1950s and early 1960s (for more information see Fisher and Orth, 1985; Barker and Efford, 2004). These efforts were largely unsuccessful, although one staphylinid beetle (Staphylinus (Ocypus) olens) showed potential; however, the use of this species as a biological control in orchards has not been actively pursued (Sakovich, 2002). In 1966, however, another (opportunistic) predaceous snail, the decollate snail Rumina decollata (of European origin) was found to have invaded California (see Pictures). Experimental releases of R. decollata in southern California citrus orchards were begun in 1975 and, in most cases, resulted in complete control (displacement) of C. aspersum (Fisher and Orth, 1985). Rumina decollata is now used to control C. aspersum in some 20,000 ha of citrus in southern California, but is currently permitted only in certain Californian counties (Dreistadt et al., 2004). As this predatory snail consumes young to half-grown snails, control is achieved only in 4-6 years. Sakovich (2002) recommended first using molluscicidal baits to reduce the population, and then combining skirt-pruning and copper barriers with introduction of R. decollata. Once control by R. decollata is achieved, maintenance of copper barriers can cease, R. decollata can be harvested and transferred to new areas. However, Cowie (2001) expressed concern regarding both the effectiveness of R. decollata in control of C. aspersum, its potential impacts on native (even endangered) species and its potential as a garden plant pest.

A study by Altieri et al. (1982) was carried out in a daisy field in northern California to determine the effectiveness of the indigenous coleopterous predator Scaphinotus striatopunctatus in the biological control of C. aspersum. Release of the predator in the field under light metal sheets, together with colonization by garter snakes (Thamnophis elegans) from an adjacent field, resulted in a significant reduction in snail populations.

In South Africa, the native predacious gastropod Natalina cafra was investigated as a potential biological control agent against C. aspersum, with special attention to the possibility of establishing a viable population of the natural enemy in captivity (Joubert, 1993), but this approach seems not to have been implemented.

Research by the Entomology Division of the Plant Protection Department, Cukurova University, Turkey, on the importation of predators and parasitoids as biological control agents (mainly for citrus pests) included the coccinellid Hippodamia convergens as a potential predator of C. aspersum (Uygun and Sekeroglu, 1987).

Ducks, chickens or guinea fowl can provide long-term control in citrus orchards and vineyards, if an appropriate breed is chosen and properly cared for. Growers take the animals each morning into the orchard for as little as half an hour to scavenge for food. This solution can be very effective but involves extra labour in managing the animals and protecting them from predators (Sakovich, 2002; Davis et al., 2004).

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:

Impact

In general, there is very little information on the economic damage terrestrial snails and slugs cause to vegetable crops and fruit trees. It has been estimated that Spanish farmers apply 2500 tonnes of molluscicides a year, at a cost of 1000 millions pesetas (£5 million) (Castiellejo et al., 1996). Annual control costs in California, USA, are estimated to exceed US$7 million. In fruit farming, up to 50% of the harvest has been lost as fruit damaged by snails is affected by Monilia fungi (Stringer, 1969; Stringer and Morgan, 1969).