Helen Yemm on how to get rid of destructive ladybirds and overgrown nettles
This week Helen Yemm advises on how to deal with unwanted invaders of both the plant and insect variety, and saving a flowering favourite...
Fly away ladybird, make way for the rat-tailed maggot?
Last summer I involved my grandchildren in nurturing a brood of ladybird larvae, only to realise that I was rearing monsters – not the children, but the larvae. These turned out to be those of harlequin ladybirds, which are destroying our native ladybird population. What should I do in future?
Harlequins have been making murderous inroads for over a decade now and their progress is still being monitored. My personal view is that there is not a lot we gardeners can do. Frantically squashing a dozen or so hibernating harlequins that find their way into window crevices is not going to make a significant difference to the state of play.
What we are witnessing is “bio-homogenisation”, the displacement of a native species by a small number of highly successful invaders. It is a problem that vexes conservationists all over the world. Logging the progress of the harlequin ladybird helps in our basic understanding of the phenomenon, so you could perhaps do this with your grandchildren (see harlequin-survey.org).
This year, though, why not introduce them to some other less enthralling garden insects? The “snorkels” of ghastly-but-fascinating rat-tailed maggots can sometimes be found in stagnant rainwater before hatching into beneficial hoverflies. Then there are spooky black-and-shiny long-legged ground beetles that hide away in dark corners and scuttle about doing all manner of good. Or build a simple insect “lodge” with them. Above all, keep at it.
How can I get rid of nettles and brambles?
I am renovating an overgrown garden abundant in brambles and nettles. Is there anything I can use to control these and not harm nearby shrubs?
Gill Osborne, via email
If your nettle patches are relatively small, you might choose to deal with them without resorting to weedkillers. They are quite easy to fork out of the ground since their sideways-spreading roots are near the surface and their deeper, yellow roots will not regrow as long as you remove these pale-pinkish surface ones.
Once thoroughly dried off, the rooty debris can be composted. With older, more matted patches, clear off last year’s dead stems, allow them to reshoot to about 20cm, then dose them with Roundup, using a watering can rather than a sprayer to avoid “drift”. Protect foliage of your shrubs and any other wanted plants as necessary.
Roundup (glyphosate) kills all greenery, but does not spread in the soil so does not damage naked woody stems or underlying roots. Get rid of brambles by vigorously stabbing at their roots, severing them with a spade and destroying all the pink dormant buds to be found some 20cm below ground. It is tough but satisfying work. Or cut them down to about 30cm from the ground and carefully paint the remains with SBK Brushwood killer.
They will take several weeks to die. Meanwhile, the weedkiller (triclopyr) will take about six weeks to break down in the soil. Both these powerful chemicals are harmless to one and all after application once they are dry and, used carefully according to the manufacturer’s instructions, should not harm your existing shrubs.
My Daphnes dear: is it one down, one to go?
Two years ago one of my two thriving, four-year-old Daphne odora ‘Aureomarginata’ plants began to lose its leaves and develop distorted flower shoots and knobbly areas on the branches. I dug it up and disposed of it, but now the second one seems to be going the same way. Can I save it?
Judy Parsley, via email
Daphnes can be fussy beasts. The yellowing and dropping leaves that you describe are generally caused by drought or waterlogging, to both of which they are extremely sensitive. But this sounds to me more like a virus, to which some daphnes are also highly susceptible.
It is likely that the virus was passed on from one to the other, very possibly via sap-sucking insects of some sort. I know you don’t want to read this, but I think that you should kiss the second plant goodbye, clear up all the leafy debris and start again.
If you absolutely must replace one or both of them (I know I would be bereft without at least one in my garden) aim to plant them elsewhere, and even spray them preventively in spring, after the flowers have faded, with a contact and systemic insecticide such as Bug Clear Ultra. Then keep your green fingers crossed.
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Write; Helen Yemm, Gardening, The Daily Telegraph, 111 Buckingham Palace Rd, London SW1W 0DT
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Email; helen.yemm@telegraph.co.uk
Helen Yemm can answer questions only through this column
