Slug it out
Tuesday 29th October 2013, 12:41PM GMT.
Imagine a Britain without vegetable patches, allotments or beautiful flower beds, where gardeners are unable to grow anything outside, knowing any plants will be ravaged by a foreign predator.
This is, admittedly, a worst case scenario, but still not an impossible one, says scientist Dr Ian Bedford, head of entomology in the John Innes Centre in Norwich. He is leading a group of scientists in a project to monitor sightings of the Spanish slug, Arion vulgaris, a particularly aggressive and large slug which breeds and eats at a faster rate than our native species and has so much slime on its body many native predators are put off.
The scientists launched a website, slugwatch.co.uk, a couple of weeks ago, asking people to report sightings. Within 10 days, there had been 18,000 visitors to the site and more than 800 submissions, some reporting the Spanish slugs, Dr Bedford confirms.
He says that the reports from the public may also give scientists an idea of whether ‘Arion vulgaris’ is breeding with native species to form a hybrid that combines the worst of the Spanish slug with the tolerance to frosts and cold from our own species.
This year has generally been a bad year for slugs. Late spring frosts killed off a lot of them, but this may just be offsetting the plague that could follow – we need late spring frosts and early winters to kill off juvenile slugs to keep numbers down.
Last year, however, was a different story as, following a mild spring and wet summer, Dr Bedford found Spanish slugs ravaging his own garden in Norfolk.
“The only vegetables which survived the onslaught were parsnips,” he recalls. “They attacked legumes, onions and chives. They ate broad beans, French beans and runner beans and were going to the top of the plants and eating them from the top downwards. I couldn’t get carrots past early germination stage and the same with lettuces and beetroot.
“All the potato foliage was eaten, although I did manage to harvest some potatoes, and the foliage of onions was also attacked, which resulted in very small onions.”
He had evidence of Spanish slugs eating snails and even working their way through dog faeces and eating dead animals such as mice.
Growing plants which slugs don’t like may provide some solution for domestic gardeners, though.
“The plants which don’t seem to get attacked by slugs are the ones which have high levels of plant oils, such as rosemary, which has high levels of camphor, and lavender,” explains Dr Bedford.
Other plants not favoured by slugs include azaleas, pieris, geraniums, mature shrubs and conifers, although Dr Bedford points out that last year Spanish slugs ate his buddleia and rudbeckias.
Contrary to reports, slug pellets will kill Spanish slugs but because of their voracious appetite they will eat a lot of slug pellets before they die, he notes.
It’s better to go on slug patrol early morning and at dusk, preferably after rain, as these huge slugs are highly visible, and pick them off before putting them into a bucket of water containing detergent which will cause them to sink, he advises. Then dispose of them and bleach the bucket to kill off any bacteria.
Winter digging may also help expose the eggs, which look like an off-white jelly about a quarter of the size of a pea. They are generally laid up to 5cm under the soil surface, or under logs and stones, or terracotta plant pots.
Slugs are nothing new to gardeners nationwide. On average a UK garden is home to more than 20,000 slugs and it is estimated that an acre of farmland can support more than 250,000 of the slippery creatures.
The RHS takes a more cautious approach regarding how great a threat the Spanish slug is to our gardens.
Guy Barter, head of RHS advisory service, says: “We are not clear what the threat is or how widespread it is likely to be. At this point there’s no reason to be anxious about it. We need more evidence.”
He notes that Spanish slugs, unless they are juveniles with two stripes down their back, are not easily distinguished from other slug types and believes it’s going to be difficult to identify Spanish slugs from the descriptions gleaned from visitors to slugwatch.com. He says confirmations will require dissection in adult slugs.
Still, now the rain has stopped, I shall venture into my garden, bucket in hand, searching for those slimy monsters… and perhaps you should do the same.
- Cyclamen hederifolium
Their stalks coil, bringing the developing seedpods to ground level, where they will self seed if left undisturbed. Autumn-flowering cyclamen should be planted in summer near the soil surface in well-drained soil which has been enriched with well-rotted leaf mould. They go ideally in dappled shade under trees and shrubs, where the ground will be dry during the summer months.
- Good enough to eat – Rhubarb
Unless you plan to use crowns for forcing on a regular basis, there’s no reason why a plantation can’t continue to grow for up to a decade and just a few crowns will give enough rhubarb to feed most families.
Rhubarb thrives on fairly heavy soil enriched with a heavy dressing of well rotted manure or compost. Ideally the pH should be slightly acidic. Crowns should be ready for planting any time from November through to March while ground conditions allow. They should be planted 90cm (3ft) apart in either direction, at a depth where the buds are not more than 5cm (2in) below the soil surface, and make sure you firm them down well.
During the first year a strong root system will be formed and it’s best not to harvest the sticks so that all food produced by the foliage is channelled towards building up the crown, thus allowing better cropping in subsequent years.
Although rhubarb is not a high-maintenance crop, keep the soil fertile by applying a top dressing of manure or compost in February and forking it into the soil surface, carefully avoiding damage to the crown.
- Top buy – Shed tidy
What to do this week
- Order seed catalogues so you can snap up all the varieties you want before they are sold out.
- Clean metal tools, removing soil and washing them thoroughly after use.
- Remove dirt and sap from secateurs using lubricant or household cleaner, wiping clean with a tissue.
- Remove submersible pumps and lights, cleaning filters and drying them off before storing.
- Complete the planting of all new evergreens, including conifers.
- Lift and store maincrop carrots and potatoes.
- Begin winter digging, adding well rotted organic matter to improve the soil.
- Divide and replant waterside plants such as astilbes and trollius.
- Finish planting up containers for the spring.
- Prune autumn-flowering deciduous shrubs over three years old as they finish flowering.
- Lilies for forcing can be brought into heat around 13 weeks before flower is required.
- Dry off achimenes and set under a bench until needed. In spring, they can be repotted.
- Feed winter cherries with a dilute solution of liquid manure.