Sue Whigham shares experience and advice on how to deal with honey fungus
We’ve always had a part of the garden where I’d try out interesting shrubs only to find that they turned up their toes after a couple of years. Most disappointing was the Azara microphylla that never put on any fresh growth and got scrawnier and scrawnier. Actually, I think that it would have been a slightly disappointing shrub if it had survived as its relative, Azara serrata is much more exuberant and deliciously scented. Little did I know. There’s a lovely specimen at Great Dixter with its bright, bright yellow flowers just at the right height to immerse yourself in their fragrance as you pass.
So then we planted pittisporums, early flowering viburnums and all manner of other things. They’ve gone now and the only plants that are doing well are a medlar (great for showy autumn colour) and a healthy bay tree. Never mind, there is still a good show of oriental irises which we inherited.
Honey fungus tends not to touch perennials, luckily. And we’ve now got the perfect spot for a giant trampoline firmly secured to a trellis to save it from becoming airborne any time soon.
So what is the problem? Well, everything came to a head after the dry summer of 2021 when several mature, multi stemmed hornbeams started losing their leaves early, as well as suffering branch dieback. Then this year the leaves seemed to be smaller and generally sickly. A big patch of honey fungus mushrooms several feet away from one of the stricken trees confirmed the worst. The trees had most probably been harbouring honey fungus for years and the drought and the fungus combined to reduce the trees to shadows of their former selves. So three have now been felled. I’m trying to convince myself that, rather like after the 1987 storm, there’ll now be opportunities to make a few changes in the garden. Luckily, not all garden shrubs and trees will succumb to the fungus. There are some that don’t seem to be affected. One of these is box (Buxus) and thank goodness for that. Box has its own problems with both box blight and box tree moth caterpillars though. Repeated applications of TOPBUXUS ZenTari followed by TOPBUXUS Health-Mix sorted out the caterpillars this year and stopped them in their tracks. Wise though to use pheromone traps to catch the male moths in the spring and to nip any infestation in the bud. The added bonus of the traps is that they are specific to male box tree moths and will not attract or kill other moth species.
There are a number of honey fungus species native to the UK of which Armillaria gallica and Armeria mellea are the two usually found. Of course honey fungus is in most of our precious woodlands but doesn’t always cause too many problems in this sort of setting. The reason being that other fungi present compete with the honey fungus and restricts its progress. In a cultivated garden setting we are not so lucky as the honey fungus has less competition from other fungus and can run unabated through susceptible trees and shrubs. There is no ‘cure’ for it, either natural or chemical, but there are steps you can take to stop or weaken any possibility of further havoc.
I think that once mature trees are affected, there is a problem in that as it is spread from root to root, so it’s difficult to recognise before it is too late. Red or purple rhizomorphs maturing into what look a bit like black bootlaces are to be found in the root system of the tree and white mycelium can be found under the bark. Apparently the rhizomorphs can extend 30 metres from an infected plant, which is a worrying thought! There is a suggestion that you can sink a plastic barrier into the soil to a depth of eighteen inches with an inch or two above the soil if you think that you might have a chance to catch the fungus in time. Again, tricky if the trees that are affected are mature and thus their roots really extensive. I think that at that stage, you might have to live with it after removing as much of the affected plant as possible.
It is only later in the fungus’s progress that you will spot the clumps of large honey coloured mushrooms appearing in late summer. These are, of course, the final giveaway. They vary in size and shape and are very recognisable because of their size and by each mushroom having a white ring of tissue known as the annulus just under the cap.
Smaller trees and shrubs can be protected to some extent by thoroughly mulching and fertilising as well as watering regularly in dry summers. The other thing is to remember to add a good sprinkle of beneficial mycorrhizal fungi, naturally present in the soil, around the roots of new plantings (Rootgrow is easily available). Trees and shrubs planted a little too deeply with soil or compost piled up around their base are more likely to be damaged as the fungus can spread through their root collar. The advice too is to leave the ground fallow for up to a year before replanting after you have removed as much damaged material as you can.
Check whether any new plant you intend to introduce is capable of withstanding the fungus if you definitely know that you have it. The RHS, amongst others, publish a very comprehensive list of plants that are not affected. It would seem sensible to stick to those. The only one on the list that I would take issue with is the flowering quince. Ours seems to be about to succumb having battled through several seasons of poor growth and now a peeling bark – but you never know, it may be something else. And I’m sure that it might have preferred a less exposed spot. Another note to self.
Sue Whigham can be contacted on 07810 457948 for gardening advice and help in the sourcing and supply of interesting garden plants.
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