I grow Viburnum opulus mainly for its autumn colour and scarlet berries and don't take much notice of it at this time of year. However, I was shocked to notice that the shrub has completely nibbled leaves – some have small holes and others are reduced almost to shreds. I can't see anything actually doing the damage – has it done the deed and flown away? What action should I take if any? Veronica Gray, via email
The leaf nibbling and shredding is the work of the grubs of a nasty pest, the viburnum beetle that also commonly attacks the popular evergreen Viburnum tinus. These larvae may have vanished from view but they are not far away – pupating in the soil beneath the shrub. They will emerge in a month or so as hungry adult beetles and feed on the foliage of the host shrub until early autumn and deposit their eggs on its woody stems. These will over-winter and hatch next spring, and so the merry-go-round continues – unless you take action, that is.
There is not a lot you can do at the moment – I am told that lightly cultivating the soil beneath the shrubs to disturb and reveal the pupae is tempting, but not necessarily effective unless perhaps you have a hopelessly tame robin virtually sitting on your shoulder while you do it. To save your shrub (since repeated attacks that go unchecked could kill it), and in an attempt to interrupt the life-cycle of the beetle, you should try to catch the adults as, or even before, they do damage in late summer. I suggest spraying with a systemic and contact spray containing thiacloprid – Provado Ultimate Bug Killer Ready Mixed. Next spring, as the leaves unfurl, have another go with the spray bottle in case you missed a few, giving rise to a new generation of larvae. This is one you can win, with a bit of effort.
Almost as a post script to the above, I will mention another grubby little number, the gooseberry sawfly larvae which, to emailer Janice Sayer's horror, has stripped the leaves off her fruit bushes. These are, if anything, worse than the viburnum beetle, no fewer than three generations being active during a single growing season.
An eagle eye, followed by hand-picking of the grubs (which are hard to spot since they start on the undersides of leaves at the base of bushes and work upwards from April onwards), is recommended. Or spraying with thiacloprid (Ultimate Bug Killer) as mentioned above. Janice should now feed her bushes with a general fertiliser and give them a big drink to help them recover.
Reverting to type
Five years ago, I planted a fuchsia with pretty pink, cream and grey-green leaves. I cut it back each spring (as advised by you a long time ago), which makes it a neat, side-spreading bush. However, although it still flowers well, it is gradually becoming less interesting because more and more of the shoots are turning up with green leaves, even though I cut them back as I believe you should. Chloe Bartram, via email
Variegated and coloured-leaved plants such as this are basically attractive ''freaks'' that have been propagated for their freakishness. With some, it would seem, the process is fragile and the plants are capable of reverting to their original green state.
Variegated acers, euonymus and eleagnus are some of the worst offenders that spring to mind – and of course, this beautiful fuchsia is pretty tricky – but other shrubs seem to be fine. I have never had a problem with a variegated pittosporum reverting. The green shoots are naturally more vigorous than coloured shoots since they contain more chlorophyll, and will thus eventually start to dominate the plants and take over.
Cutting reverted green shoots in these circumstances sometimes makes the problem worse, since if you prune out only half the offending branch, it may immediately make more new all-green shoots from the axils of lower leaves. The safer course of action is to cut cleanly back to the main stem from which the reverted shoots come. However, in the case of your fuchsia you may find that it has gone too far. It may be simpler to replace it. You could try propagating from some of the remaining coloured stems (nip off a few soft, flower-less shoots in late summer, remove lower leaves, pot them in a very sandy compost and keep them covered and in the shade). Or, simpler if you haven't the time/inclination/aptitude/facilities to fuss over cuttings and you have a couple of brass farthings to spare, you could simply dig up the old plant, buy a new one and armed with this information, keep an eye open for the first sign of reversion in future.
The all-powerful ant
As things hot up in the garden, I tend to get letters and emails about ants: ants taking up residence under lawns and leaving unsightly mounds of soil (poor David Bostock and Mr and Mrs Laughton), ants invading pots of Fiona Campbell's ornamentals and shrubs and ants taking up residence in compost heaps.
Something must be done, you say, but what? Ants are the Superpower, the garden Master Race, outnumbering us by about a squillion to one, yet the damage they cause is not that great. They annoy the lawn perfectionists, who can find themselves spending a lot of time with a brush or besom trying to disperse the mounds, and ants can cause wilting and eventual death of the occasional plant by shifting soil around between plant roots which they don't much appreciate. Ants prefer to make their homes in dry soil, so watering invaded pots every day for a few days may send them to find somewhere else to live. Stirring compost heaps regularly may do the same. As the Laughtons have found out, you are on a hiding to nothing using ordinary ''domestic'' ant killer outside, so for those desperate to get the upperish hand, there is a biological control from Nemasys called No Ants, available from, among others suppliers, Green Gardener (01603 715096; www.greengardener.co.uk ).
Bits and bobs
Bridget Clark remembers that I mentioned a type of copper ''paint'' that you can apply to timber-edged veg beds (among other things) to stop slugs and snails, and asks if I could repeat the details. The product is Copperbed and as far as I know is only available from the manufacturers (0845 225 2118; www.copperbed.co.uk). Julie Henson's mother was told once by an old-school gardener that you could not use molehill soil on a veg patch because it is poisonous. Is this true? I should imagine that this idea came about when moles were ''dealt with'' by putting worms treated with strychnine into their runs. This practice is now outlawed. Molehill soil, being deeply excavated by our pesky little velvet-coated friends, is wonderfully weed-seed-free and commonly used by canny gardeners as an ingredient for potting composts.
Steve Smowton has an invasive grass messing up a clump of saxifrage. The problem worsens as the season progresses and instead of pulling out cleanly the grass snaps off. Is there a solution, he asks? It sounds as though this could be the dreaded couch grass that spreads via invasive snappy rhizomes. Couch is more easily removed if the invaded plant is dug up completely and the white rhizomes pulled out backwards, as it were, via the underside of the affected plant. Steve does not tell me much about the variety of saxifrage and some tend to have the kind of root system that falls apart when dug up, so the whole cleansing adventure could come unstuck. But I thought the basic technique with couch grass was worth mentioning nevertheless.
- Write to Thorny Problems at firstname.lastname@example.org or Gardening, The Daily Telegraph, 111 Buckingham Palace Road, London SW1W 0DT. Helen Yemm can answer questions only through this column.