Tuesday 12 December 2017

Diarmuid Gavin: How to diagnose and tackle the most common garden problems

Leaves wilting? Bark discoloured? Crops failing? Our horticultural expert diagnoses the most common garden problems - and tells you how to treat them

Diarmuid Gavin checks on an applet tree. Photo: Fran Veale
Diarmuid Gavin checks on an applet tree. Photo: Fran Veale
Diarmuid Gavin at the garden he designed in Dundrum Town Centre. Photograph: ©Fran Veale
Help carrots by companion planting
Spraying for aphids

Gardening is about having fun and growing many different plants that have arrived on our shores from around the world. However, looking after a plot is not always easy - and plant problems make up the main questions gardeners with all levels of experience ask when they meet me.

Never are these issues more apparent than during the warm, muggy weather which midsummer in Ireland brings.

Thankfully, today it's much easier to identify gardening and plant problems and look for solutions yourself than in years gone by. The gardening community makes for a very active online resource. There are many websites dedicated to your gardening joys and issues - and it can be a good starting point if you have mysterious green problems.

Today, I am going to tackle three of the most frequent garden problems we have to deal with - generally revolving around the damage done by pests and diseases to plants.

Diarmuid Gavin checks on an applet tree. Photo: Fran Veale
Diarmuid Gavin checks on an applet tree. Photo: Fran Veale

I have my magnifying glass at the ready: it's time to take a close look at three of the top culprits: canker, black bean aphids and carrot root fly.


The first common garden problem is canker, which can affect apple trees, pears, mountain ash and hawthorn. One of the most popular apples, Cox's Orange Pippin, is particularly susceptible.

Canker is a fungus that finds its way into bits of damage on any of these trees. It could kill the tree. It's identified through little circular or oval sunken bits of dead and discoloured bark.

Remove the infected branch or twig at once using a very sharp, disinfected pruning saw. Burn all the infected material - don't put it anywhere near a compost heap, where the fungal spores can fester.

Prune your trees in dry weather and apply canker paint onto the cut surface.

If you do use chemicals - which I don't - spray with a preparation that contains copper, something like a Bordeaux mixture.

Black bean aphids

Spraying for aphids

These are nasty little things that don't only attack beans and peas. Every gardener will have seen them, but we mightn't be able to put a name to them.

If a soft plant in your garden - the beans or the peas or even ornamentals such as roses - are not doing well, if they are wilting a little bit, suffering from low production, leaf curling or if the foliage is yellowing, then have a good look. On the underside of leaves, you may find an infestation of these horrible creatures. They can be up to a couple of millimetres in length, are oval-shaped and black or dark olive green. They group together where the feeding is good and, as they suck the sap from the leaves vampire-like, they leak a kind of honey dew that drips on the foliage underneath, which then gets covered in a black mould.

And it gets worse. Once these aphids have decided there are too many of their friends on the one plant, some of them sprout wings and daintily fly off to start again on some new juicy foliage.

Their eggs are produced in the cooler months of the year and successfully overwinter. What's even worse is that when these rascals hatch, they themselves can produce five new live babies per day - which start sap-sucking immediately!

What can you do ? One of the friendlier chemicals these plants can be treated with is pyrethrin but there are also some simple and deeply satisfying methods of control.

For example, you can use your garden hose as a pistol - wash them away in your own jet stream. Pick off the infected bits of foliage, encourage ladybirds and create homes for birds, because many insect-loving species will have a field day with these dark delights.

Carrot root fly

Help carrots by companion planting

The final garden issue to tackle of today's trio is the carrot root fly. As the name suggests, these pests burrow through the soil and feed on the roots of carrots.

As they do this, they release a smell which attracts their friends. They also attack other plants, such as celery, parsley and parsnip.

They lay their eggs in soil near the carrot, and it's the larvae which emerge after a week that do the damage. You'll know you have them by a reddening of the carrot leaf and then the inevitable wilt. When you lift the root, you will see the tunnels they have burrowed.

You can help the problem by some companion planting - put in something else that smells not so nice to the larvae, such as garlic or onion. Remove the damaged plant to avoid spread.

You can choose a carrot variety such as Flyaway, which isn't so susceptible. Also, covering the crop with a barrier of horticultural fleece will help, because the flies that lay the larvae won't be able to land near the plant. But do tuck in the fleece.

Gardening will always be a challenge. Some crops will be successful, while others will provide food all right, but maybe not for you. The challenge is what makes it interesting!

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