Slug Control
From Allotments4All
Common pests and how to deal with them
- Pest type: Mollusc
- Order: Stylommatophora
- Scientific name: Deroceras reticulatum
- English name: Field slug
Signs of infestation: The slugs are easily visible on soil and plants especially in the evening and early morning, and leave trails of shiny mucus.
Symptoms of infestation: Large ragged holes in soft leaves, with smaller stems cut through and pitted areas in soft fruits such as strawberries as a result of their rasping mouthparts. Plants may be completely eaten away.
Biology, reproduction and spread: The slug over-winters under debris and in the soil in the egg and adult stage, and within the crowns of plants as an adult. At 5oC the adult will slowly become active, and eggs will take three months to hatch, although they will hatch within three weeks at 20oC, and adult activity is most apparent in spring and autumn, during moist, warm, conditions. They produce mucus to assist their movement on the soil and on plants. Slugs are hermaphrodite, they need to mate, but all can lay 20-50 eggs. These can be found in the soil, at the edges of paths and under debris. There are around three generations a year, and adults may live for 2-3 years. They feed mostly at night, or in shady, damp conditions days, on all parts of plants at or just above soil level, prefer softer tissue, and move from plant to plant destroying crops. They prefer alkaline soils, above pH 7.0. As temperatures fall, they crawl to hibernate under debris and the surface of the soil.
Prevention and control treatments and methods.
Physical and cultural: Hand pick and destroy active slugs morning and evening. Check plants regularly for signs and symptoms of infestation. Copper strips, sharp sand, ashes and grit can be placed around choice plants as a deterrent. Encourage natural predators like frogs, toads, hedgehogs and birds by providing ponds and dense cover for habitats. Cultivation of the soil in very cold, dry weather exposes slugs and eggs, which may die or be eaten. Plants with woody stems tend not to suffer from slug attack, and Allium sp. tend to be unaffected. Traps filled with beer can be used, the slug is attracted to the beer, but cannot escape. Debris where slugs can hide should be removed.
Biological – together with benefits and limitations: Introduce a parasitic nematode such as Phasmorhabditis hermaphrodita. This is purchased as eggs that are mixed with water and applied to the soil. They need a minimum temperature of 5oC but are more active at around 20oC. They need moist soil conditions to move around in the soil, and enter the slug’s body releasing a bacterium. This causes the slug to stop feeding and eventually it dies. The benefit of using this method is that it is harmless to humans and other creatures, so crops can be eaten safely, and predators can eat the slugs. The nematodes will need to be applied repeatedly every six weeks for best effect.
Chemical: Apply slug pellets containing metaldehyde, or a soil drench containing aluminium sulphate.
Legislative: None
How the pest affects the health and vitality of the host plant: Leaves, stems and fruits are damaged or destroyed. If only small sections of leaf are damaged, the plant may recover, although growth may be stunted. Heavy infestations will kill the plant.
Contents
Using Coffee
Scientists have stumbled on a secret weapon against snails and slugs. They have discovered the garden pests are poisoned by caffeine.
A strong cup of coffee is enough to send the creatures into a writhing frenzy, followed soon by death.
Scientists think caffeine acts as a potent neurotoxin against the pests.
The finding may be of use to gardeners and commercial growers. Slugs and snails are notoriously difficult to deter from attacking plants.
The chemicals currently used to control them are not permitted as residues on food crops.
Caffeine - regarded as safer and more environmentally acceptable - could be very useful in pest control.
Special brew
The discovery was made by scientists at the US Department of Agriculture's Agricultural Research Service in Hawaii.
They were testing a caffeine spray against frog pests when they noticed slugs were dying.
Follow-up studies showed that a 1-2% caffeine spray was enough to kill snails and slugs.
Even at concentrations about 100 times weaker, the slugs lost their appetite.
A cup of instant coffee contains about 0.05% caffeine, while brewed coffee contains more.
Lead researcher Dr Robert Hollingsworth says because caffeine is a natural product and is classified by the US Food and Drug Administration as safe, "it has potential as an environmentally acceptable alternative toxicant for the control of slugs and snails on food crops."
Natural high
There is a catch. Caffeine at 2% concentrations can damage the foliage of plants or cause yellowing.
It may be possible to overcome this by mixing caffeine with a polymer, say the researchers, who report their findings in the journal Nature.
But not everybody is convinced that caffeine is environmentally friendly.
Dr David Bohan, of the UK agricultural research institute IACR-Rothamsted, told BBC News Online: "1-2% is a very high concentration of caffeine.
"That might be potentially damaging to plants and invertebrates other than slugs such as insects."
Physical Barrier Methods
Copper
Available as copper backed adhesive tape to stick around plant pots.
Egg Shells
Most effective if dried in the oven and crushed up prior to use.
Going on a bug hunt
If dissuasion isn’t working you may want to consider going on a ‘bug hunt’ to reduce slug numbers on your allotment. You will need to employ different methods depending on whether you intend going on a day time or a night time hunt. During the daytime, slugs hide away in cool, damp dark environments. So if you want to catch them you will need to reduce the numbers of inaccessible hiding places such as cracks in the soil and half filled bags of compost left out in the open. At the same time you will need to increase the number of slug hideaways which you can easily check during your daytime slug searches.
Dispensing slugs is not a pleasant experience, some people carry a small pair of garden scissors to simply cut them in half, others drop them into a small pot of salted water or paraffin. Alternatively you can skewer them on a needle or hatpin and put them into a dark plastic bag. Once dispensed into a dark plastic bag slugs will not be inclined to crawl up into the light. When you have collected all the slugs you can find, you can tie a knot in the bag and simply put it in the dustbin. You can increase the number of slugs you find by baiting favourite hiding places with favourite slug foods, like lettuce or cabbage leaves.
Night time hunts are most productive about an hour after dark. A head torch, popular with campers and climbers, is a particularly useful piece of equipment for night time hunts, since this ensures you have two hands free for wielding scissors or picking up slugs to drop into paraffin / strong salt solution.
Slug traps
Slugs love yeast,bran and milk.
