Nail those snails, slice those slugs

 

It's time to fight back against the unfriendly forces that are creeping towards our plants, writes Jane Powers

All gardeners know that what we are doing is really a form of warfare. We may yammer on about nurturing seedlings, being creative with colour, making strong statements with architectural foliage and so on. But the fact remains that our efforts take place on a battlefield, where armies of critters hide in the trenches, float in by parachute or march relentlessly across our territory. These unfriendly forces are bent on destruction, mowing down our seedlings, blasting our colourful creations with germ warfare and stuffing our architectural foliage into their ever-hungry maws. And that is grounds for war.

As any successful campaigner will tell you, if you want to gain the upper hand, you must get to know your enemy and plan your attack. Now, at the start of the season, is the time to hold a council of war. First of all, there's no point wasting time on earwigs, woodlice and other slightly annoying invertebrates who do half-hearted vandalism to our plants. No, as I see it, most Irish gardeners must contend with five main opponents: molluscs, aphids, vine weevils, glasshouse pests and four-footed marauders.

SLUGS AND SNAILS

Let's take the worst first: molluscs, also known as gastropods (which translates rather graphically as "stomach foots"). But not all are harmful to plants. The enormous, greenish, camouflage-clothed slugs that hang out in the compost heap feed on fungi and rotting matter, and are not interested in living vegetation. It is the small and medium-sized slugs (and snails, of course) that are the culprits, attacking plants above and below ground.

The war with these blubbery battalions must be fought using many tactics: with barricades, traps, one-on-one combat, biological weapons, low cunning and, most importantly, enlisted allies. Barriers, for instance, may be erected around vulnerable plants or seedlings: these may be collars made from plastic bottles or copper (which repels slugs and snails); exclusionary rings of hostile material such as grit, wood ash, dried and crushed egg shells, dried grass clippings, coffee grounds or various off-the-shelf preparations. Pots may be girdled with petroleum jelly (messy) or copper tape. All blockades, however, must be continually maintained, and not all are effective in every garden.

Beer traps are useful in confined spaces: shove small containers of fresh beer into the soil, leaving a centimetre protruding so that ground beetles (good guys) don't fall in. Remove the corpses daily, and replace the beer every three days.

Hunting and destroying, especially early in the season, before they have bred reinforcements, is a good way of controlling slugs and snails. They are out and about when temperatures exceed five degrees, favouring moist and dark conditions. Continual night-time forays with scissors and head torch will eventually reduce numbers (as well as your squeamishness).

Ferramol, organic slug pellets based on iron phosphate, are harmless to non-molluscs. They are not as effective as traditional slug baits, but they can be used as part of a many-pronged battle plan. Biological control, in the form of the parasitic nematode Phasmarhabditis hermaphrodita (sold as Nemaslug), is expensive, but it is an option for small spaces or greenhouses.

Confusing the enemy is a valuable strategy: make vulnerable species such as hostas and lettuce less obvious by interplanting them with unpalatable plants. (This also confounds cabbage white butterflies and carrot flies.) Grow dark-leaved plants, such as red lettuces and other dusky vegetables, as these are less troubled by gastropods. And make the garden more welcoming to the birds, frogs, hedgehogs and ground beetles that are predators of molluscs by planting a diverse range of vegetation and making a wildlife pond. Enlist some ducks.

GREENFLY AND BLACKFLY

Friendly wildlife will also gobble up aphids - enemy number two. Known also as greenfly and blackfly, they multiply at an exponential rate, reaching maturity in days, when they give birth to another generation - without having been intimate with a male aphid. Males appear later in the season, as part of a life cycle that is too complex to unravel here. Aphids are sap suckers, weakening plants by drinking their life's blood, and often infecting them with diseases. What's more, they excrete excess sap as "honey dew" (a euphemism if ever there was one), which is a perfect medium for mould. They are fairly unsavoury beasts.

A vigilant thumb and forefinger will deal with early invasions (check under leaves and at the tips of new shoots), while more established encampments may be dispersed with a blast of the hose. Often, though, nature will send deliverance, in the shape of aphid-eating ladybirds, hoverflies and lacewings - which is why spraying with poisons is a bad idea. Aphids have short life cycles compared with their predators and recover from a chemical attack in double quick time. Garlic spray, however, is worth trying. It doesn't kill anything but imparts an unfamiliar character, which is reputed to befuddle pests.

SEE NO WEEVILS

And so to vine weevils, the scourge of the nursery trade. Peat-based composts offer an ideal habitat for the eggs and crescent-shaped, dirty white larvae, which munch through the roots of potted plants, killing them from the bottom up. The long-snouted adults are dull, browny-black, hump-backed insects that gnaw distinctive notches into the margins of leaves.

Non-peat-based composts offer less attractive conditions, while a layer of grit on the surface deters the weevils from laying eggs. In the garden susceptible plants, such as primulas and heucheras, should be surrounded with grit. A parasitic nematode, Steinernema kraussei, may be used from March onwards, when soil temperatures reach five degrees.

PESTS IN GLASSHOUSES

Glasshouse pests creep up when you're not looking, reproducing in the warm climate and flocking all over your plants. Red spider mites are the most insidious, being barely visible to the naked eye. By the time you notice the symptoms (mottled and dry-looking foliage, fine webbing), they've gained a serious foothold. Damping down or misting the glasshouse regularly helps prevent them (they can't survive moist conditions). But if you've got them, you can buy a predatory mite, Phytoseiulus persimilis, to dispatch them.

Whiteflies are little floaty sap suckers that waft up when you brush a leaf. French marigolds, in my experience, ward them off (you need about one plant per square metre). If you don't believe in marigolds, then the little predatory tropical wasp Encarsia formosa will do the job.

CATS

Finally, we must mention the garden saboteurs: other people's cats. The young seed bed, the freshly planted bulbs, the newly weeded patch - all of these provide soft, open soil for Felix's unlovely latrine.

Urban gardens suffer most, simply because there are more households (and hence more cats) in any given space. After extensive trials on our territory, we have found three solutions. A mulch of cocoa shells prevents cats digging (and needs replacing at least annually); and Renardine, a foul-smelling deterrent, is effective if you follow the instructions carefully.

If these fail, you can always follow Shakespeare's advice: "Cry, 'Havoc!' and let slip the dogs of war." A fearless hound will make feline visitors think twice about using your garden as a comfort stop. jpowers@irish-times.ie

WHERE TO GET YOUR WEAPONS

Ferramol slug pellets and garlic spray are available from Fruit Hill Farm, www.fruithillfarm.com, 027-50710

Nematodes and biological controls are available from Mr Middleton, 01-8731118, www.mrmiddleton.com

Cocoa shell is available from Norton's, 01-4540666, 48 Francis Street, Dublin 8

Renardine is available from selected garden centres and co-ops You can get more information on biological controls from www.nemasysinfo.com.