Slugs and snails always become active when the night temperatures begin to rise towards the end of spring. Which in the UK is any time after mid-April. The first line of defence is to reach for the slug pellets and by the end of the summer millions of pellets weighing in at thousands of tons will have been scattered over the soil.
Slug pellets are classified as a pesticide and they need to be managed responsibly. I appreciate that this may sound a little over the top, but the cartons containing the slug pellets must always be locked away inside a secure store to prevent any possible threat or hazard to other humans or wildlife.
It should be remembered that slug pellets are a bait that is used to attract slugs and snails before poisoning them. And the most efficient and effective way to use pellets is to apply them to the soil before the tender young growth begins to appear on ornamental plants and edible crops. Once they have feasted on the real thing they will most likely ignore the pellets. The slime trails that slugs and snails lay down are scented to act as a guide to food or safety.
The active ingredient used in the production of the most commonly used slug pellets is metaldehyde. It is a selective pesticide that can used by gardeners to control slugs and snails over a wide variety of crops. Metaldehyde damages the mucus cells which results in the production of masses of slime eventually resulting in dehydration.
Metaldehyde is considered to represent a low risk to animals where it is consumed in small doses. However the main predators of slugs are hedgehogs they can kill up to 500 slugs per night. Alarmingly hedgehog numbers have fallen by more than a third since 2004, and have collapsed from more than 36,000,000 in the 1950’s to fewer than 1,000,000 today. A number of factors are likely to have contributed to this, including loss of hedgerows, a greater number of roads and increased house building in areas of the countryside. But it is probable that the increase of slug poison being used and the fact that slug predators are dying out are both linked to the decline.
Always follow the manufacturer’s instructions when using them. Don’t be tempted to scatter them liberally all over the surface of the soil or around the plants. The recommended application rate for metaldehyde based slug pellets is one pellet every 4 - 6 inches/10-15 cms. There is no advantage gained in leaving heaps of pellets under slates or pots. It only increases the risk of a poisonous dose to wildlife such as hedgehogs. There is also the risk of contamination of the soil.
Although metaldehyde is considered to be a low risk pesticide it is water soluble and has been entering field drains, water courses and reservoirs as a result of drainage or surface run off. Extreme care must be taken to prevent it reaching natural water supplies as it is virtually impossible to completely remove, even when using existing advanced water treatment processes. If we don’t take action to prevent this contamination then there is every likelihood that the use of metaldehyde will be restricted.
A report published by Natural England and the Environmental Agency in the summer of 2013 revealed that levels of metaldehyde were over the EU limit in a source of drinking water. The report identified the River Stour that supplies water to homes in Essex and Sussex and linked the contamination to the use of slug bait during the particularly wet summer of 2012. It has to be recorded that the Health Protection Agency states that there is no risk from the concentrations that have been detected in drinking water supplies so far. However, drinking metaldehyde isn’t good for you, neither is the pesticide good for the environment, nor pets.
To tackle this problem Water UK, a body set up to represent the water industry; along with farmers and growers have developed a successful voluntary approach to reduce the concentration of metaldehyde in rivers, reservoirs and drinking water over the past few years. If this voluntary approach isn’t effective in reducing the levels of metaldehyde it may be necessary to introduce tighter environmental restrictions, such as the enforcement of water protection zones which could provide powers to protect water at a local level – including the prohibition of harmful activities such as the use of slug control by gardeners because gardeners also share a common responsibility to ensure that the environment is protected from metaldehyde pollution.
The treatment of pesticides depends upon their physical and chemical properties. The characteristics of metaldehyde mean that it is not effectively removed using the normal treatment for pesticides that may be found in raw water. Its simple structure means that it cannot be broken down into more benign component parts by other water treatments. It is a very difficult compound to completely remove; even when using existing advanced water treatment processes.
The most sustainable solution is to prevent metaldehyde getting into any water courses in the first instance. There are a few steps that you can take to keep any risks to a minimum.
Listen to the five day weather forecast and don’t apply pellets if rain is imminent. Heavy rain may cause surface water to wash the slug pellets off the surface of the soil into nearby ponds, ditches and water courses.
Clear up any spills no matter how small they are. Don’t leave heaps of pellets lying on the surface of the soil where they can pose a risk to wildlife. Collect up and remove any packaging lying around where it can be damaged by adverse weather and also pose a risk to wildlife.
Wait until the daytime temperature is a minimum 10C/50F and 7C/42F by night before using slug pellets. If the surface of the soil is dry, water it lightly to encourage the slugs and snails.
Whenever and wherever we use chemicals in the garden we disrupt and damage the laws of nature. And there are times when we can’t repair the damage. It is far safer for humans, pets, wildlife and the environment if we look for and try to adopt safer methods of slug and snail control.