Metaldehyde

The metaldehyde used in De Sangosse pellets carries the Quality Control check: Meta quality

Mode of action

Metaldehyde is the only molluscicide available for use in agricultural crops in the UK.  It works by attacking and destroying the slug mucus producing cells.  This is don at three cell sites (membrane, nucleus and Goli apparatus) which limits the risk of Resistance.

Once the lethal dose has been ingested the slug tries to detoxify by exces mucus production, but this is irreversible and leads to slug immobilisation.  Once a slug cannot move, it cannot feed and will be exposed to drying leading to death.

There is a common misconception that because the obvious symptom is dehydration, the slug may recover by taking on ambient water. This is pure myth. Test results from Lonza (Triebskorn et al. 1998) have proved that metaldehyde irreversibly destroys the mucus producing membrane, thus disabling the slug's means of locomotion, skin protection and digestion, making it impossible for slugs to rehydrate and recover.

There is also a misunderstanding about the efficacy of metaldehyde in wet conditions. Again research has shown that mode of action is unaffected and in laboratory tests where excess water was introduced, no significant difference was recorded between wet and dry conditions. This means that slugs that have consumed a lethal dose of metaldehyde will NOT recover after heavy rainfall.

Furthermore, in temperature tests metaldehyde has been proven to work in conditions as low as 2°C, below those in which slugs are usually active. (Mallet and Bougaran, 1971)

As long as a pellet is visible it retains metaldehyde and activity.

Metaldehyde is the most commonly used molluscicide over the last 60 years.

Non target organisms

Studies have shown that metaldehyde based pellets if used correctly do not cause harm to:
Hedgehogs: Gemmeke H. 1995 Nachrichtenblatt des Deutshen pflanzenschutzdienstes 47:237-40
Bees: Speiser B. 2002 Encyclopedia of pest Management 506-508
Birds: Campbell LH & Cooke AS 1997 Joint Nature Conservation Committee 18pp
Game/rodents: Thompson JP et al 1995 Human & experimental Toxicology 14: 437-45
An animal repellent (Bitrex) is included in all the following products to deter domestic animals and field mammals from consuming slug pellets.

Beneficials
When implementing a control strategy growers and their advisers should be aware of beneficials that can help to protect the crop and keep slug levels manageable through natural means. When applying chemical control methods you should always be mindful of what effect it will have on creatures other than the targets. For further information on this take a look at the products section.
Hedgehog picture: Courtesy of Lonza

Predators
Most birds will eat slugs, as will hedgehogs, rats, shrews and badgers. Toads, newts and occasionally slow worms also include slugs in the diet. The slug is primarily nocturnal, feeding at night when it is cool and damp. Daytime feeding is rare, as the slug has no means of regulating water loss from its body. However the number os slugs eaten by the predator is usually too low to be an effective control strategy.

 

Carabids
Many species of ground beetle, known as carabids, will eat slugs. They are small black beetles and are found across the country in all conditions. Particularly fast moving, they are often seen scurrying across the ground. Of these beetles the violet ground beetle has shown to be the most voracious consuming maybe one or two slugs a day, while Pterostichus melanarius will eat one slug every two to three days. Pterostichus melanarius is the only significant carabid that lives in cereal crops.

Devil's coach horse (Staphylinus olens)
This creature belongs to a large group known as Staphylinidae that numbers in excess of 1000 species in Europe. It is quite capable of flying with larger ones usually flying by night. Devil's Coach Horse are predators and omnivorous scavengers, with slugs making up a major part of the diet.

 

Leatherjackets (Tipula spp.)
The larvae of the daddy long legs or craneflies. Leatherjackets hatch in grassland usually in September. They feed in the soil and underground and will come to the surface in moist, warm conditions. Activity is reduced in cold weather. Despite their beneficial effect on slug populations, leatherjackets themselves can become pests in large numbers, causing damage to young plants' root systems.

Environmental Concerns
When used responsibly and as directed on the label metaldehyde based slug pellets represent minimum risk to the environment and the user. However it is important that guidelines be followed as, with any agrochemical, misuse can put animals and creatures at unnecessary risk. For full information on use and storage of metaldehyde products please look at the safety data sheets or product labels and for information on using traps.
Activity by aerobic and anaerobic micro-organisms in soil cause metaldehyde to decompose quickly to acetaldehyde and subsequently to CO2 and H2O.