Things take a dark turn in the garden…

While moving turf and digging out new beds I’d noticed lots of very tough, long, dark roots all over the garden. They looked similar to the long tap roots of cinquefoil – the perennial weed Potentilla reptans. But I never saw any top growth. And these roots were mostly travelling horizontally, a few inches below the surface, rather than down. And they really were long – too long for cinquefoil. And then finally, I realised what a dolt I’d been. They’re not roots, but rhizomorphs – it’s the dreaded honey fungus (or as it’s also known, bootlace fungus, after the long, black rhizomorphs that grow out for great distances).

Rhizomorphs on a section of tree root

My only excuse for not realising sooner is that up until now, I’d never seen it before. The two dead trees we inherited in the garden should have been a good clue. Entering panic mode, they had to go; starting with the biggest, right in the centre of the garden…

That took some effort! I felt a bit guilty burning it, but I did at least wait until the wind was in the right direction, so that the smoke blew away across the fields, rather than back towards the neighbours. And the guidance is to burn infected material. Mind you, it was still smouldering late into the next day! I’m now trying to cut up what’s left for a more controlled burning experience.There are a couple of roots still there under the grass, heading out in different directions – we’ll need to lift the turf and dig them out too. I may hire a chain saw for the other dead tree!

There are, apparently, five different varieties of honey fungus, or Armillaria, only two of which are generally found in gardens. I think we have A. gallica, which has large, easily visible rhizomorphs. Thankfully, this is considered to be the less damaging variety. The other, more destructive variety, A. mellea, has rhizomorphs that are much less visible, so very difficult to find. Looking on the black side, I suppose this means we could have that too! Let’s hope not.

These evil rhizomorphs have spread across much of the garden…

There are no chemical treatments for Armillaria. The only things you can do are to dig out and destroy infected material (difficult, if not impossible), bury impermeable barriers to a depth of around half a metre around infected plants or stumps, or around healthy plants you want to protect (difficult, if not impossible) and to use plants that are less susceptible to honey fungus. But apparently no plants are immune, and the data around which are more, or less susceptible seems questionable. The RHS list, for instance, has Pyrus (pear) in the least susceptible group, and Choisya (mexican orange) in the most, whereas Gardening Which says exactly the opposite! And the RHS contradicts itself in different articles. In their defence, they do point out the problems in identifying susceptible species – those that are most reported are likely to be those that are most prevalent (and/or, most valued) in gardens.

So; what’s our plan to eradicate this pernicious enemy?

  • Remove the dead trees (including as much of the root system as possible),
  • Hold off with any more tree planting for now – hopefully by the autumn, deprived of their food source, most of the rhizomorphs will have died (good riddance!),
  • Cultivate (i.e.; dig over!) as much of the garden as is reasonably possible. Go through the ground with a fine-tooth comb (alright; a hand fork!) and pick out as much rhizomorph as possible,
  • Keep on digging down around the trees we’ve planted (but not too close; we don’t want to damage their roots) to head off any actively growing rhizomorphs,
  • Hope for the best!

The dry weather may well be helping us, drying out any rhizomorphs left in the ground.

It’s not all doom and gloom. The white lilac (Syringa) in the chicken run has just flowered, and looked (and smelt) a treat…

And the Iris sibirica we brought with us in pots is flourishing…

text & images © Graham Wright 2020