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Garden pest problem? Launch the predators

by John Dean

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Lacewing credit: nutmeg66

It can be war in the garden when it comes to pests but as more people realise the damage done by chemicals, they’re turning to friendlier forms of combat.

One of the best solutions is to let nature fight your battles. There’s a whole army of beneficial bugs and other animals that eat garden pests such as aphids, vine weevils, slugs and snails so it’s worth doing as much as you can to attract them to the garden.

Ben Raskin, Head of Horticulture at the Soil Association (www.soilassociation.org) , says: “Such an approach is a cornerstone of organic growing and can be very effective.”

“In small gardens, planting to attract predators can be absolutely brilliant. Where the approach struggles is with larger, commercial-size sites where predators cannot handle the scale of the problem.”

Plant for predators: get rid of aphids

Hoverflies such as the marmalade fly are some of the most useful insects to attract because their larvae are enthusiastic eaters of aphids, the tiny green or black bugs that descend on plants, sucking their sap and stunting their growth. Lacewings meanwhile can deal with a whole range of pests.

“The carnivorous larvae will eat aphids, mealybugs, thrips, caterpillars, immature white flies and pest insect eggs,” says Celia Hammond, London Wildlife Trust’s Southwark Area Manager who is based at the Centre for Wildlife Gardening (www.wildlondon.org.uk). Although as larvae they eat bugs, when they become adults, hoverflies and some common green lacewings feed on pollen and nectar and so they can be tempted into the garden by certain plants. Try plants with umbrella-like flowers such as fennel, dill, angelica, cow parsley and wild carrot or those with daisy-type blooms such as dyer’s chamomile and ox-eye daisy. “The flat, open nature of the flowers makes pollen and nectar readily available to hoverflies, most of which have relatively short mouthparts,” says Andrew Halstead, Principal Entomologist at RHS Garden Wisley (www.rhs.org.uk).

Lacewings, and another aphid predator, ladybirds, can also be encouraged into the garden by providing homes for their winter hibernation. “You can make your garden or allotment ladybird-friendly by growing herbaceous perennials and shrubs and not cutting them all down in the winter so that ladybirds have somewhere to hibernate,” says Hammond. There are also ladybird and lacewing hotels available to buy.

Using plants to control pests is an approach that has been practised in vegetable gardens for many years. Some flowers are used to attract beneficial bugs or to lure pests away from prize crops while others are chosen for their potential pest-repelling powers.

Sue Berger, author of Allotment Gardening: An Organic Guide for Beginners (www.backlanenotebook.wordpress.com), says: “My favourite companion plant is the nasturtium. I sow the dwarf nasturtium Alaska Series, which has very lovely mottled green and cream leaves that look great even before the brilliant orange flowers appear. I sow these around the base of broad beans which are prone to blackfly. The nasturtiums attract this aphid from the plants, gathering it on the undersides of their leaves.

Pot marigold credit: Arthur Chapman

“Pot marigold is a key companion plant and helps to attract bees, butterflies and hoverflies to the vegetable patch. The French marigold helps to deter whitefly so I surround the edges of the brassica bed with these traditional cottage garden flowers.

“Other strong-smelling plants, such as mint and garlic, may repel pests that are attracted to plants by their scent, thereby keeping them away from nearby vegetables.

Guy Barter, Chief Horticultural Adviser at the Royal Horticultural Society, is a little more cautious about the efficacy of this approach however. He says: “Companion planting with marigolds is often favoured. We are not entirely convinced by this, but it is attractive and probably does good in some cases.”

Homes for heroes: make habitats for slug, snail and vine weevil hunters

While slugs and snails chomp their way through any available greenery, vine weevils also produce grubs that eat the roots of plants, causing them to wilt and die. They can be a particular problem in containers.

Luckily though, frogs, toads, hedgehogs and predatory ground beetles eat all of these pests and providing the environments they like is one of the best ways to attract them.

All you need to encourage frogs and toads to visit is a small pond. This will also attract dragonflies which hoover up small insects.

Hedgehog credit: WillBurton2

It’s important that hedgehogs have good nesting sites so provide a pile of leaves in a quiet corner or perhaps a purpose-built hedgehog house if you can. Before you do this though, it’s worth making sure that hedgehogs can get into the garden – they need 15cm square gaps at the bottom of boundaries.

Attracting predatory ground beetles, such as the violet ground beetle, is a good idea as they have immense appetites and can eat their way through a large number of slugs, snails and vine weevils. Introducing a log pile, leaf litter or just a small pile of broken crocks and stones into the garden is a good way to encourage them because many are nocturnal and so need somewhere dark to hide during the day. There are also plenty of other invertebrates that are happy to chomp their way through a range of pests. “There are many species of parasitic wasp that develop inside and eventually kill garden pests. Other general predators found in gardens are centipedes, spiders, staphylinid or rove beetles and anthocorid bugs. Add to that all the viruses, bacteria and fungi that can infect and kill pests, it makes you wonder why there are any!” says Halstead.

Thrush with broken snail shell credit: greensnapper2011

Birds are also pretty effective at dealing with all sorts of pests. Thrushes enjoy snails while starlings and crows are particularly partial to leatherjackets, which can kill off grass as well as small plants in flower beds and vegetable plots. Tits meanwhile are brilliant for eating smaller insects such as aphids, caterpillars and leaf miner grubs. Nesting boxes and feeders are worth providing and, according to some recent research at the University of Reading, there’s no danger that the extra food will spoil their appetites. You can read more about attracting birds into urban gardens here.

Bats hoover up many small insects too and a bat box is a good idea.

As well as creating new habitats, it’s worth thinking about preserving the ones you’ve got. Cutting back perennials in the autumn, for example, may take out hibernating insects so it‘s best to wait until the spring. Many insects hibernate in grass tussocks so it’s also worth leaving a corner of the lawn untouched if you can.

The main requirement for this approach to pest control though is patience. “It can be disheartening for a first-time gardener who has this blank canvas to work with because the pests tend to move in first. However, in time, the garden will establish a natural balance and the predators will come,” says Mr Raskin.

Bring in the bugs

If beneficial bugs and other animals haven’t arrived in sufficient numbers to get the pest problem under control, it’s possible to buy in nematodes – microscopic worms that occur naturally in the soil and prey on common pests.

There are all sorts of varieties, including those that prey on slugs, vine weevils, leatherjackets and chafer grubs. There are many suppliers who can advise on the best way to go about introductions.

Traps and barriers can also be useful. For vine weevil problems in container gardens, insect barrier glue can be used around pots. Barter says: “Many gardeners use slug and snail traps, which in small gardens can catch many molluscs. Barriers, whether copper or drying to keep out slugs, or mesh to exclude insects, can also be used.”

He has words of encouragement too: “Because organic gardeners use compost and avoid heavy feeding, plants grown by organic methods tend to be less susceptible to pests and diseases than plants grown by other means, which greatly helps control.”

Useful web links:

http://apps.rhs.org.uk/advicesearch/profile.aspx?pid=506

 

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