Monday, March 21, 2011

slugs, every gardeners enemy!

Slugs and snails are molluscs, the same as oysters and clams (a bit of trivia there!). They are comparable in structure except that the snail is protected by a hard, calcareous shell that makes it less susceptible than slugs to dry conditions and sun exposure. When adverse living conditions confront snails, they react by sealing the opening of the shell with a mucus sheet, which soon hardens to a leathery texture. The snails can then become inactive and have the ability to remain in this condition for up to 4 years.
Slugs range in size from 0.5 to 20cm in length, depending on species and age, with colour variations of dark brown and black to light gray. Slugs and snails are creatures that slither along on a path of mucus. This mucus dries out and can be seen in the daytime as a shiny trail over leaves, fruit and soil. The discovery of these "slime trails" may be the only way of determining their being there, as slugs and snails by and large feed at night. Sporadically they come out of their hiding places and feed in the evening or on dreary days. For this reason, many growers do not attribute the obvious damage to slugs and snails, as the pests themselves are not observable. When trails and damage are observed, the slugs and snails can often be found on the ground close to the injured plants, hiding under decaying plant debris, stones, clods of soil, or logs.
Slugs and snails feed on the lower leaves of numerous plants particularly in the areas between the veins. Juvenile slugs and snails damage plants by rasping away the exterior tissue, while adults eat holes through the leaves, nip off tender shoots or cause total annihilation of seedlings. Damage to the leaves, along with blustery weather, time and again causes leaves to shred. Compost piles, drain pipes, litter heaps,  greenhouses, well walls and uncultivated areas with dense plant growth, provide ideal sites in which the gray garden slug, gray field slug and snails are capable of overwintering in all developmental stages.
Slugs and snails feed on plants such as Hostas,petunia, zinnia, salvia, lily-of-the-valley, bean, the fruit of tomato and strawberries, lettuce, Brussels sprouts, cabbage, pepper and many other young vegetables we’re growing really.
These molluscs are more troublesome:
 During prolonged periods of wet, overcast weather. In crops with a dense protective canopy. In gardens that are heavily mulched and/or surrounded by tall grass and weeds.
 In areas containing debris such as decaying leaves, poles, boards and logs. Limited control of slugs and snails can be obtained by adjusting the above situations where possible. If damage persists, chemical control may be necessary. It is important to note that a combination of control methods is much more effective in reducing population levels.
Cultural Control Methods
Hygiene - hygiene can be highly beneficial in controlling populations of slugs and snails. It involves the removal of all materials that could provide daytime hiding places and ideal egg laying sites, such as plant debris, dense plant growth, rocks, boards, and logs. This is especially important in shaded areas near trees and buildings. The use of mulches should be avoided in any of these sites. Tall or densely growing plants may need to be thinned to allow for more air movement and light penetration and therefore, drier environmental conditions.
Barriers - Slugs and snails avoid crawling over any dry abrasive material such as gravel, sharp sand, wood ashes, diatomaceous earth, or lime. The increased production of mucus required to free themselves of these materials exhausts them and soon causes death. A 30-45cm  band of any one of these inert materials spread along borders or between rows of plants would be a beneficial repellent.
Fly screening, the green windbreak material, approximately 10cm wide will also provide a successful barrier against slugs and snails. This screening should be partially imbedded in the soil for support to a depth of 5cm and completely surround the plant. When using the screening on a cold frame, it should be tacked across the top of the frame leaving the cut edges of the screen sharp.
Traps - Traps are a successful method of control in small areas, boards, bark, or a comparable material at least 15cm square can be positioned in the garden close to those plants which are susceptible to slug and snail assault. These traps should be checked each morning so the slugs and snails can be removed from beneath them and destroyed. even though handpicking is labour intensive, one hour of doing so will give a noticeable reduction in populations.
Stale beer placed in a container, to a depth of about 2.5cm is extremely attractive to slugs and snails. These containers can be sunk into the soil so that the top edge is at ground level and placed 3 m apart throughout the garden. The slugs and snails will crawl into this container and drown. These traps should be put out early in the evening when feeding activity begins and emptied regularly as slugs and snails accumulate.
Natural Predators - Slugs and snails have natural enemies such as toads and several species of ground beetles and their larvae, wild birds and ducks, with the toad being the most important. It is highly beneficial to encourage such predators to reside in your garden to maintain a natural balance.
Control Methods
Chemical Control - Molluscicides such as metaldehyde or methiocarb are available in bait form for use in the control of slugs and snails. Baits are sold under several trade names in garden supply and hardware stores. Metaldehyde is registered for use in vegetable crops, while Methiocarb can be used on ornamentals and lawns only. Follow label direction to ensure safety and efficacy of each product. There are 'safe' baits you can use based on higher concentrations of iron phosphate that will only harm snails. These go under names like 'Escar-go' and 'Sluggo'.
Diatomaceous earth is a powder that will scratch snails and slugs causing them to loose moisture and die.
Copper repels slugs and snails so if you can surround an area with copper, you can discourage invasions.
Nemaslug,(available from Mr Middletons in Dublin, or at onlinev outlets) Phasmarhabditis hermaphrodita (a member of the Phylum Nematoda family)
Nematodes are the latest and it seems the most effective way of controlling slugs, this beats the chemical alternatives easily. Nematodes are tiny organisms, so small they are invisible to the eye. They are naturally occurring organisms which are harmless to you, your kids, wildlife and your plants.
The idea is to them in plastic packages, put them into a watering can, add water and then water the areas affected by slugs. The little nematodes then enter the slugs and release bacteria which slowly kills the slug. Even better news is that the nematodes then multiply and go in search of more slugs! It does work -however the soil temperatures have to be warm.
I’ll try and write a bit about other common pests, diseases and possible solutions when I get a bit of time,
I hope this has been helpful,Andy


The Secret Gardener said...

Great piece Andy and for those with a slug/snail hatred a great little book is 'The little book of slugs' by Allan Shepherd and Suzanne Galant

This has over 70 different ways to combat these pests without any suggestion of toxic pellets.

Simon said...

My beds are surrounded by paths made up of pine needles, stone and ash. That does help as a barrier. sell a bio-slug pellet made up with Ferramol, made in Ireland.
Lamping slugs at night - i.e. going out with a torch and a knife at dusk is pretty effective, for everyone you kill, it stops hundreds.
To improve traps, put them away from crops but bait with dried catfood - this also attracts hedgehogs
I also spray my pathways with home made weedkiller, this contains salt so is a good deterrent during dryer spells