Up to this year we had a row of some 20 Phlox along the side of the
decking. They were planted in the 8” gap between the decking and the
East-facing 8’ stone gabions that support the ground beyond our property.
They grew profusely and bore a myriad of flowers each summer, visited
especially by moths and butterflies. This area gets a lot of sun to early
afternoon, and is a sun-trap, it can be warm even on a snowy day. In summer
it can be very hot. Each year after flowering the Phlox are cut back and
then left.

This year most of the Phlox failed to thrive, and some have died. Digging
one up revealed a white fungus around the roots, of a thin stringy
appearance, with small clumps of it located around the roots. There is no
fungus on the stems or leaves. Also planted in this area are a couple of
Spring-flowering Clematis Montana Wilsonii which grow well, and one of
these is located half way along the row of Phlox, which are book-ended by
two 6’ tall Taxus.

When these houses were built some 20 years ago, it is believed that the
builder used sub-soil to form the gardens. Most owners have not developed
their gardens, some have been covered in weed-control fabric since the
original owners moved in. The clay soil remains in very poor condition
despite all attempts to improve it; any new shrubs take at least two years
to ‘find their feet’ and start growing. Whenever the soil was disturbed,
our garden would smell of Armillatox for some days; this went on for some
years. We haven’t found fungus anywhere else.

Location is South Devon, the garden runs East to West.

My questions are…

What fungus is this?
What methods of treatment are available?
Which treatments are most successful?
Will the fungus spread to other plants?
What precautions to avoid spread should be taken?

TIA for any guidance with this issue.

--
Spike

On 15 Aug 2023 11:08:38 GMT, Spike <aero.spike@btinternet.invalid>
wrote:

>Up to this year we had a row of some 20 Phlox along the side of the
>decking. They were planted in the 8” gap between the decking and the
>East-facing 8’ stone gabions that support the ground beyond our property.
>They grew profusely and bore a myriad of flowers each summer, visited
>especially by moths and butterflies. This area gets a lot of sun to early
>afternoon, and is a sun-trap, it can be warm even on a snowy day. In summer
>it can be very hot. Each year after flowering the Phlox are cut back and
>then left.
>
>This year most of the Phlox failed to thrive, and some have died. Digging
>one up revealed a white fungus around the roots, of a thin stringy
>appearance, with small clumps of it located around the roots. There is no
>fungus on the stems or leaves. Also planted in this area are a couple of
>Spring-flowering Clematis Montana Wilsonii which grow well, and one of
>these is located half way along the row of Phlox, which are book-ended by
>two 6’ tall Taxus.
>
>When these houses were built some 20 years ago, it is believed that the
>builder used sub-soil to form the gardens. Most owners have not developed
>their gardens, some have been covered in weed-control fabric since the
>original owners moved in. The clay soil remains in very poor condition
>despite all attempts to improve it; any new shrubs take at least two years
>to ‘find their feet’ and start growing. Whenever the soil was disturbed,
>our garden would smell of Armillatox for some days; this went on for some
>years. We haven’t found fungus anywhere else.
>
>Location is South Devon, the garden runs East to West.
>
>My questions are…
>
>What fungus is this?
>What methods of treatment are available?
>Which treatments are most successful?
>Will the fungus spread to other plants?
>What precautions to avoid spread should be taken?
>
>TIA for any guidance with this issue.

Not all root fungi are harmful. Many are beneficial to both plant and
the fungus. Known as Mycorrhizal fungi. I don't know if phlox benefit
though. https://www.rhs.org.uk/biodiversity/mycorrhizal-fungi But
remember, it was a very dry early summer.

--
Chris

Gardening in West Cornwall, very mild, sheltered
from the West, but open to the North and East.

Chris Hogg <me@privacy.net> wrote:
> On 15 Aug 2023 11:08:38 GMT, Spike <aero.spike@btinternet.invalid>
> wrote:

<snip>

>> This year most of the Phlox failed to thrive, and some have died. Digging
>> one up revealed a white fungus around the roots, of a thin stringy
>> appearance, with small clumps of it located around the roots. There is no
>> fungus on the stems or leaves. Also planted in this area are a couple of
>> Spring-flowering Clematis Montana Wilsonii which grow well, and one of
>> these is located half way along the row of Phlox, which are book-ended by
>> two 6’ tall Taxus.

<snip>

>> My questions are…
>> What fungus is this?
>> What methods of treatment are available?
>> Which treatments are most successful?
>> Will the fungus spread to other plants?
>> What precautions to avoid spread should be taken?

>> TIA for any guidance with this issue.

> Not all root fungi are harmful. Many are beneficial to both plant and
> the fungus. Known as Mycorrhizal fungi. I don't know if phlox benefit
> though. https://www.rhs.org.uk/biodiversity/mycorrhizal-fungi

> But remember, it was a very dry early summer.

Many thanks for the interesting link.

It would seem that the section headed ‘Endomycorrhiza (mycorrhiza living
within a plant)’ might apply to what we found on the Phlox roots, which may
have suffered from a very dry April.

Mrs Spike is a keen user of mycorrhizal fungi, but we can’t remember if it
was applied when the Phlox went in.

--
Spike