Greenfly and other pest problems

28. June 2020 by Isabelle Van Groeningen
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Honigtau & Blattläuse © Isabelle Van Groeningen
Honigtau & Blattläuse

Flagge Deutschland für deutsche Übersetzung – zur deutschen Version – Gardening is more than going about smelling roses – like the greenfly. You are regularly confronted by enemies that are out to attack your plants. This season the pests seem to have been about in great numbers. There is little you can do about some of them, other than letting nature take its course and wait for it to pass. Sometimes you can give a gentle helping hand, that does not necessary involve the use of chemicals.


As I walk through my garden, I will often just squish greenfly or horrible black aphids that colonise my lovely plants. I will step on a slug that ventures onto the path. These may be small, but important actions that may prevent the situation developing into a major problem.

Keep a watchful eye out for your plants so you can intervene before the damage gets too severe. I did not, and have to face the consequences. One of my all-time favourite plants in my shady garden is the very elegantly structured Solomon’s Seal. This week I noticed I had missed the first signs of sawfly; whose larvae resemble grey caterpillars. They stripped my plants completely.

All that is left after just a few days intensive feeding are the main stems and some leafstalks. In past years I managed to pick off and destroy the young larvae and eggs as soon as I spotted the first damage. This year I somehow missed it. I will cut back the stems. I doubt they will produce new growth this season, but leaving them standing as a sad reminder is no option. Their elegant stems will be back next spring.

Box tree Caterpillar

A plant where vigilance is really important is box. Regularly checking your hedges or topiary will enable you to treat them as soon as a problem arises. At the Garden Academy we have set up a treatment programme that has enabled us to keep our hedges fit and healthy. Part of it is preventative, building up the strength of the plants, and thereby increase their resistance against Boxblight, but for the young caterpillars vigilance is important so we can apply the biological Bacillus thuringiensis before it is too late.

Buchsbaum-Zünsler - Junger Buxuszünsler © Isabelle Van Groeningen
Young Box tree Caterpillar

In my parent’s garden in Belgium, the boxplants have remained largely healthy, not thanks to a vigilant eye, but thanks to a sound ecosystem in the garden. We have observed birds, as well as other predatory insects such as wasps feeding on the caterpillars so that the pest populations are kept under control.

What do you have to do to create a garden with a happy, healthy balance of animals and insects that will support you in your daily struggles? Change your mindset. An immaculately tidy garden with lots of tidy bare soil, in which no weed is allowed or no leaf is left, is a recipe for disaster.

Establishing a healthy ecosystem

A variety of habitats with a wide mixture of different plants, including natives, are the start. A few “weeds” (mostly valuable native plants) tolerated in amongst your garden plants provide a feeding ground for many garden inhabitants.

Look after your birds. They are not only entertaining; they are very valuable. Provide food, water and nesting possibilities. They heavily rely on insects to feed their young and will repay your generosity with the systematic removal of pesky aphids and juicy caterpillars. Watch blackbirds picking through your borders, or blue tits flit from bush to bush: they are not there to smell your roses!


Blattläuse © Isabelle Van Groeningen

Where the new rose shoots have been touching my windows, myriads of tiny sticky droplets had been deposited by the greenfly that colonised the tender shoots a few weeks ago. Similarly, about a month ago, every plant in my garden was covered in a thin shiny film from the sugary excreta of greenfly that had obviously invaded the Oak above. I know this sticky problem from Lime trees, but it is the first time this has happened to our oak. There was nothing I could do: treating the problem (i.e. the greenfly) was out of the question, so I just had to grin and bear it. As if by magic, it has all disappeared. The greenfly on the roses have vanished. The invasion has been tackled by the numerous natural predators, be it birds or other insects like hoverflies, lace wings or ladybirds. In many cases, their larvae have the greatest appetite.

As with everything in nature, nothing is left to chance. Everything has its purpose. Even the irritatingly sticky mess is there for a reason: many insects, including bees, feed on the sugary substance.

What reassures me is that in most cases, plants will recover rapidly. There may be some disfigured leaves or stunted growing tips where sap-feeding insects damaged cells at a young stadium, these can easily be pinched out similarly to giving the plant a Chelsea chop (see Blog 24th May 2020: Chelsea Chop and the Flowershow).  Even in the case of exotic pests that arrived on our shores without their natural predators, our native inhabitants discover their gastronomic value sooner or later.

On the whole, a little patience, and a pinch of tolerance, will see you through the worst of it.

Artischocke - artichoke © Isabelle Van Groeningen
Artichoke – happy without greenflies…
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