Jamie wrote:

A little late in the day I've spotted some unusual, and localised,
plant death. I've lost a large bracken which I noticed not growing
beyond around April this year - it looks like it stalled. Around the
same time a 9 ft walnut sapling seems to have lost all its growth
and is just now starting to produce some new growth. Part of a grape
vine was growing thinly up the walnut branches and that has all
died - the rest seems normal though I need to check more closely.
And a nearby ash sapling has gone rather mutant in its limited
growth.

It does sound a bit like overspray from a weedkiller.

I did wonder if a late frost had done for the bracken, but the
then very early growth wasn't frost burnt; the area is near
to the house; and a second walnut close by is unaffected.

The malaise seems localised around the first walnut which was
just starting to make itself obvious above a 6 ft wall. It has
had a very small branch which was almost growing over the wall
cut off by the neighbour, and I suspect something rather more
drastic may have been done. Does anyone know of a likely place
to turn to, to test the plants and soil for various unfriendly
chemicals?

Look no further than the walnut tree itself. Their roots produce juglone
a herbicide that will kill or seriously discourage competitors
underneath. Having said that narcissi and grass grow OK under mine.

There may well be a list somewhere of plants that will grow under a
walnut tree. Certain species roots and harsh conditions will be worse.

Analysis for traces of unknown herbicide will be very expensive and
probably not return any useful information.

Regards,
Martin Brown