In The Garden

red spider mite
red spider mite
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THE LATEST tips, advice and information crucial to maintaining your oasis of green space.

Radio panel tackles pests

SO MANY of us turn detective at this time of year, trying to identify the pests which have feasted on our flowers or decimated our crops.

But even the experts can get it wrong. Only last week at BBC Gardeners’ World Live in Birmingham, the panellists from BBC Radio 4’s Gardeners’ Question Time told one gardener that gypsy moth was likely to be the culprit behind the webbing which appeared on, and caterpillars which defoliated, his cotoneaster.

However, further investigation revealed it wasn’t likely to be the source of the problem, as these insects are so rare in this country.

RHS entomologist Andrew Salisbury reckons it’s much more likely to be the hawthorn webber moth, which is much more common in Britain.

The affected parts of the plant are covered in silk webbing produced by the caterpillars so, at first sight, it could be mistaken for the work of spiders.

The only control is to inspect plants for signs of webbing and damage in late spring and late summer. If the infestation is confined to a few shoots, prune them out. Otherwise, you may need to use an insecticide, such as pyrethrum.

Thankfully, many pest problems are easier to identify. Whitefly, for instance, are a familiar sight on ornamental plants and vegetables. These white-winged insects suck sap from underneath leaves and the foliage becomes coated with a black sooty mould.

Hanging sticky traps among plants and using organic sprays based on vegetable oils or fatty acids can minimise the problem.

Matthew Biggs, a panellist Gardeners’ Question Time, suggests: “One novel method of removal is to knock the leaves and suck up the whitefly with a vacuum cleaner as they fly up into the air.”

Another common problem is scale insects, the sap-suckers found on the leaves and stems of a range of plants, which hide under protective shells which vary in shape and colour.

Again, plants are weakened and ‘honeydew’ secretions on leaves become affected by a black sooty mould, particularly in damp weather.

To control scale insects on fruit trees and roses, treat them with an environmentally friendly winter wash in early winter. Ornamental plants can be sprayed with organic sprays.

Vine weevil is another scourge of gardeners, eating the roots of plants so that by the time the plants start to wilt, there’s no going back.

Adults are about 10mm (1/2in) long, black with pale orange spots. They hide in the dark during the day but move slowly on leaves at night, eating notches in leaf margins.

The plump white larvae mainly feed on the roots of containerised plants which simply wilt and die.

In spring and summer, take a torch in the garden to check plants, pick off adult weevils and crush them.

Encourage natural enemies. Vine weevils and their grubs are eaten by a variety of predators such as birds, frogs, toads, shrews, hedgehogs and predatory ground beetles.

A biological control of the larvae is available as a microscopic pathogenic nematode (Steinernema kraussei), which can be purchased from suppliers of biological controls.

Apply it in August or early September when the soil temperature is warm enough for the nematode to be effective (5-20C/41-68F) and before the vine weevil grubs have grown large enough to cause serious damage.

If your detective skills aren’t great and you’re struggling to identify the pests attacking your plants, cut off a piece of plant with the offending bug, pop it in a sealed container or bag and take it to your garden centre where staff should be able to help.

Best of the bunch — Campanula (bellflower)

These summer-flowering favourites come in a range of sizes and colours, but among the most popular are the Canterbury Bells (C. medium) and the milky bellflower, C. lactiflora, an upright, branching type which produces sprays of bell-shaped flowers from early summer to early autumn. Its flowers are in shades of white to pale blue, lilac-blue or violet and it grows to 1.5m (5ft).

If you want a smaller type, C. carpatica ‘Blaue Clips’ is a superb, compact campanula which flowers throughout summer, producing masses of blue, upright, bellflowers. It thrives in sun or shade and is ideal for rockeries, borders and pots.

Campanulas need a good moist and well-drained soil with plenty of organic matter mixed in. They can usually tolerate full sun as long as the soil is not dry, but generally semi-shade is preferred.

Good enough to eat — tending your tomatoes

Your tomatoes should be growing fast now, especially with the warm spring we had. Some will already be producing flowers and needing tying in to their stakes at regular intervals.

Regular watering - but not waterlogging - is vital. If you water spasmodically, drenching the plant one day and then leaving it to dry out, the fruits are likely to split at the bottom or you’ll get blossom-end rot, where the bottom of the fruit goes brown, hard and inedible. Water the soil, not the plant, as tomato leaves and stems hate getting wet.

Continue to pinch out any shoots that develop between stem and main branches, as they take up valuable energy from the developing fruit.

Cut off the top of plants, certainly of outdoor ones, when six trusses of fruit have begun to set, to help concentrate the plant’s energies.

Feed plants with a tomato feed high in potassium fertiliser when the plants are beginning to fruit.

Be warned that allowing your tomato plants to sit in cold water in a plant saucer is likely to make them vulnerable to fungal diseases such as tomato blight, the bane of every tomato grower’s life.

Three ways to ... Boost your raspberries

1. Bury new plants a little deeper than their previous soil level.

2. Water well in dry weather, especially while flowering and fruiting.

3. Propagate from healthy suckers growing away from the main plant.

What to do this week

Water hanging baskets and containers daily to stop them drying out and deadhead your bedding plants regularly.

Prune early-flowering shrubs such as lilac and deutzia which have finished flowering.

Make a sowing of winter-flowering pansies for a display next winter or spring.

Remove growing points from early peas which have finished flowering to concentrate energies on pod production.

Boost gladioli with a liquid feed.

Remove young green gooseberries for cooking or preserving, leaving enough to mature for dessert.

Cut back rock plants after flowering and trim trailing and invasive plants in the rock garden.

Deadhead roses to encourage repeat flowering unless the roses are being grown for the colour and profusion of their hips.

Take cuttings of carnations, fuchsias, herbs and shrubs to root in the greenhouse.

Sow turnips to produce a crop in autumn.

Make sure pond levels are kept topped up.