As a miniature munching army crosses from the Continent, we need to be on guard against a major threat to our ancient woodlands

AS a gardener, it is hard enough to learn all the rudimentary basics of how to grow each particular variety of plant without having to learn (usually through bitter personal experience) how to control and eradicate every pest and disease that happens to pass by. Just when you think that you have it all under control in the garden and greenhouse, something else comes along to throw you all out of kilter.

Imagine then a pest that can not only strip the leaves off a mature garden tree overnight, but that can also bring you, the gardener, out in an allergic rash as you contemplate the damage. I am talking about a brand new terror campaign about to be waged in our own back gardens by the invading oak processionary moth.

The caterpillars of the moth are a pest not only because they eat large amounts of leaves on the oak tree, but also because their tiny barbed hairs detach from their bodies and contain a toxin which causes irritation to people and animalsf skin, nose, ears, eyes and throat. In extreme cases, it can cause anaphylactic shock.

The oak processionary moth (Thaumetopoea processionea) is a major defoliator (eats all the leaves) of oak in Europe.

The caterpillars feed on the foliage of many species of oaks, including English, Sessile and Turkey oaks. Hornbeam, hazel, beech, sweet chestnut and birch are also reported to be attacked, although mainly when growing next to severely defoliated oaks.

The oak processionary moth is a native species of central and southern Europe, where it is widely distributed, but its range has been expanding northwards, presumably in response to climate change and nursery importation. It is now firmly established in northern France and the Netherlands, and has been reported from southern Sweden.

More recently, colonies of larvae have been found in parts of London.

Eggs are laid from July to early September.

Each female lays between 100 and 200 eggs on twigs and small branches in the canopy. The eggs are deposited in rows in a single layer to make up a plaque. The plaques are covered with greyish scales and remain on the branches over the winter. The first stage larvae hatch from the eggs in April, which means that they will be coming out any minute now.

The newly-hatched larvae have a uniformly brown body and dark head. As they grow, they lighten in colour so by the time they are mature, they have a grey body and dark head. These older larvae have a single dark stripe running down the middle of the back and a whitish line along each side. Clumps of extremely long white hairs arise from reddish-orange warts (pinacula) along the length of the body.

Less easy to see are the many thousands of short hairs that also cover the larvae, but it is these short hairs that contain the irritant toxin. The hairs present on larger larvae contain an urticating defensive toxin, thaumetopoein, a chemical potentially harmful to humans. Contact with the hairs can provoke allergic reactions manifested as skin rashes, conjunctivitis and respiratory problems such as pharyngitis and asthma. Health problems can occur even if the larvae are not handled as the hairs break off readily and are dispersed in air currents.

Abandoned nests contain shed skins, pupal cases and vast numbers of detached hairs and should be treated with extreme caution.

The larvae feed together in groups and, when not feeding, they congregate in communal nests made of white silk webbing spun up under a branch or on the trunk. The larvae typically follow one another head-to-tail in long processions to and from the nest and from one feeding position to another.

If oak processionary moth becomes established in Britain it will pose a new and difficult management problem for arboriculturalists, local authorities, contractors and tree owners. The main biological insecticide approved for use against brown tail moth, Euproctis chrysorrhoea, is currently the subject of control measures because its larvae also have easily detached, extremely irritating hairs.

As a precautionary measure, from Monday onwards, all oak trees imported from EU member states will need to have a gplant passporth to confirm the trees have been grown in a nursery and in an area free from the pest.

NEW MEMBERS WANTED THE Durham and Northumberland Fuchsia Society has recently moved from Spennymoor Leisure Centre to the Locomotion Museum at Shildon, where they hope to be holding a series of beginner meetings aimed at anyone who thinks that they might be interested in learning more about fuchsias The first of these sessions will take place in early April and will introduce the secrets of growing successful fuchsia plants. There will be no attendance costs and all cuttings will be provided by current members. Meetings would then take place on a weekly basis right through to September.

The normal society meetings take place every third Tuesday at Bowburn Community Centre from 7.30pm.

Anyone who would like any more information or would like to have a chat with member Ray OfBrien can ring him on 0191-3750493, or email him on rayoray@ uwclub.net Brigid presents the BBC Tees Gardening show every Sunday from 1-2pm.

Questions can be answered on the day by emailing brigidpress@bbc.co.uk anytime during the week, or texting 07786-200-995 and phoning 01642- 225511 during the show. Written queries can be addressed to Brigid at East Durham & Houghall College, Houghall, Durham, DH1 3SG.

Jobs this week

FLOWER and vegetable seedlings sown earlier in the month will need pricking out or potting now. Remember to hold the seedlings by the leaf and not the stem. They may have a few leaves, but they only have one stem.

THE small and weak leaves of obvious weeds such as chickweed, nettles and thistle will be popping up in the borders. Take advantage of their vulnerability and pluck them from the soil before they have a chance to grow into vigorous thugs.

*Brigid presents the BBC Tees Gardening show every Sunday from 1-2pm.

Questions can be answered on the day by emailing brigidpress@bbc.co.uk anytime during the week, or texting 07786-200-995 and phoning 01642- 225511 during the show. Written queries can be addressed to Brigid at East Durham & Houghall College, Houghall, Durham, DH1 3SG.