Sluggin' it out
Slugs are a major problem in gardens all over the world. We aim to demonstrate some of their likes and dislikes. Just how effective are 'deterrents'?
Our story of the slug is in three sections:
In most situations 100% long-term control of slugs is not possible. They are active for most of the year, they hide during the day, there can be up to 200 or more per square metre, they eat almost anything, they can survive in the soil for long periods of dry weather and can surprisingly quickly find protection under any plant or other debris when they need to. Some are large, easily seen and can be picked off plants and destroyed others are very small. Therefore before you start, assess the situation in different areas of the garden and decide your control strategy. You have the following options:
Common sense, low cost 'cultural' methods:
- grow plants which slugs dislike - but note that, apart from evergreen species, slugs eat almost anything - see our tests.
- clear away anything around or near to plants which could provide cover for slugs during the day.
- as soon as you plant anything use a torch after darkness falls, check in and around plants and remove and destroy any slugs found (but some can be very small and will be difficult to find)
- if plants need water, apply it early in the day, not as usually recommended in the evening. Aim to allow the soil surface to dry out before darkness falls.
Slug pellets offer the quickest and most effective method of controlling slugs of all sizes in many if not most situations. Used properly high levels of control can be achieved and risks to wildlife will be negligible.
So to maximise the benefits:
- Read the product label and particularly note the area treated.
- Apply pellets sparingly - a pack will normally treat a very large area.
- Do not leave pellets in heaps. Its wasteful, a slug only needs to ingest a small part of one pellet before being affected. Heaped pellets are also more likely to be found and eaten by pets or wildlife.
- Apply pellets late in the day. If plants need water, apply water early in the day and allow soil surface to dry out before using pellets. Avoid re-watering after spreading pellets for as long as possible as it tends to cause them to disintegrate and become less effective.
- Slugs eat fast and can cause damage very quickly - spread pellets sparingly around seedlings as they emerge and round transplants, eg cabbages and lettuces.
- In periods of continuous wet weather, apply pellets sparingly but frequently, possibly every 4 to 5 days.
If you do not like using chemicals, try drenching the soil with nematodes. For more information on the availability and use of nematodes for controlling slugs - www.nemasysinfo.com
Physical barriers such as sharp sand, crushed glass etc sound simple and obvious do they do any more than delay damage a few minutes. You can forget about using holly leaves as a barrier. Slugs can glide over broken glass are even reputed to be able to slide along a razor blade. We checked this out using a Japanese steel pruning saw and found that a slug will easily slide over the razor sharp edge and sharp pointed teeth!
More on control methods will be added in due course.
Slugs eat most plants. It is claimed however that some plants are resistant to slugs. Various barrier materials and repellents are available. By holding slugs in a small 'arena' it should be possible to test which plants they prefer and which materials act as repellents, deterrents or as barriers. In these Fantasy Gardening games we explain what is under test and you can see if you can predict what happens.
Test 1: large lettuce leaf overnight - how much left in the morning?
To make sure our slugs are really active, we put a large Romaine lettuce leaf into our test 'arena' and left it overnight to find out the capacity of slugs to clean up. The result shows just how much damage slugs can do in a few hours.
Test 2: stinging nettle leaves overnight - surely not to their taste?
Stinging nettle leaves were set out and left overnight. Looks like they will eat stinging nettle but perhaps not quite as willingly as lettuce!
Test 3: ranking plants for resistance to slugs
From our initial tests it seemed that there are very few plants which slugs will not eat. But they clearly have preferences? Various claims are made that they avoid or dislike agapanthus, azaleas, bamboo, begonias, cyclamen, ferns, foxglove, daffodils, evergreens, fuschias, impatiens, ivy, parsley, sanseveria, sunflowers, taxus sp, lavender, mullein, rock rose, lambs ear and viola. Contrary to these claims comfrey, impatiens flowers, parsley and sunflower leaves were eaten in our test and the flowers of daffodils were seen to be very attractive to slugs (so it depends what choice you offer).
For example, if you offer slugs a choice between leaves of lemon-scented geranium and aster and the preference is clearly aster. Offer a choice of rhubarb and lettuce and lettuce is clearly a preference.With a choice of rhubarb, comfrey and lettuce, lettuce again disappears first but both comfrey and rhubarb will get eaten. Later still and it seems that, given the choice, slugs will leave rhubarb and take the comfrey.
Plants appear to fall into one of four categories:
1 Will quickly eat a large quantity, highly attractive to slugs.
2 Will eat, but tend to leave some or take more time.
3 Reluctant to eat any.
4 Will not touch.
It may not of course be as simple as this. Perhaps damage by slugs depends on the age of the plant, different parts of the plant may be more palatable than others and there may be differences in palatability between varieties within a plant species. However, we decided to conduct a series of simple tests where we are using a small arena to offer slugs different plants or different plant parts, usually as a choice between the test plant material and a lettuce or cabbage leaf which we know is palatable to see just what happens. The results of these tests are summarised below:
|Will not touch||laurel leaf (young and old)
rhododendron leaf (young and old)
|Reluctant to eat but will try some||rhubarb leaves (young and old)
|Will eat but not quickly or completely||comfrey
|Readily eat, usually quickly||lettuce (cos and cabbage types) leaves
Test 4: Slugs and coffee
From Hilo in Hawaii comes the story that coffee can be used to control slugs and snails. Well, Sainsbury's Medium Roast Instant Coffee strong, black (without sugar) was sprayed on to Little Gem lettuce leaves to no effect. So we made some Lavazza Gold Italian coffee with likewise no effect when sprayed onto lettuce leaves. As a further check the Lavazza coffee grounds were dried, spread out and a nasturtium leaf laid on the layer of coffee grounds with other leaves as an easier option to feed on. Shortly after the leaves were laid out the scene changed. The next day all leaves had gone.
Eventually all the coffee grounds were eaten by the slugs with no immediate effect - but all that caffeine? Well, they are normally active at night so perhaps a good dose of caffeine makes little difference. So, back to the drawing board to find a really effective deterrent?
|Speed||in July 1993, Candy Johnson from Kings Lynn in the UK claimed to have the world snail racing champion when it covered 13 inches in 2 minutes 29 seconds. That's 8 metres in an hour. So slugs can travel several metres each night in search of food. A few strategically placed slug pellets or traps between cover and precious plants could reduce damage.|
|Appetite||Slugs can eat several times their body weight in plant material each day.|
|Life History||slugs lay 3 to 50 eggs each time and a total of up to 500 each year. Small slugs emerge from the eggs and grow rapidly in size in favourable conditions. They usually live for one to six years.|
|Teeth||it is often claimed that slugs have 27, 000 teeth. It is more like a rasp which is effective not only on leaves but on cardboard and, if necessary, other slugs.|
|Slime||The slime left by a slug gives off a scent which it can use to retrace its journey and help it revisit a tasty food source.|
|Strength||slugs are tough. They can move 50 times their own weight horizontally and lift 9 times their own weight vertically. This means they can easily move objects to provide protection for themselves.|
|Size||The Banana Slug in the USA reaches up to 10 inches long but is fortunately not usually a pest of gardens (unless someone knows differently?).|
|Diet||slugs eat plants, insects, fungi, worms, each other and can digest paper and cardboard (anything based on cellulose).|
Despite their low-life image, slugs are interesting creatures so there will be more to follow in this section in due course………….