Prune out any damaged branches in the spring.
Black spot particularly attacks roses and it is important
to keep them as healthy as possible so they can withstand attacks. Mulch
with a good thick layer of well rotted farmyard manure around the base
of the plants in the autumn and spring. It is also worth searching out
roses that show resistance to black spot.
Q. We have a strawberry tree (arbutus
unedo) which we planted about 7 years ago. The tree has
grown to about 18 feet, with abundant healthy foliage on the new
growth. However, the leaves seem to rapidly develop black spots
and die back, leaving only the most recent growth healthy and intact.
Any regrowth that occurs along the stem also seems to rapidly suffer
the same fate.
The supplier of the plant says that only the outermost layer
of leaves will remain in a normal specimen, but I think that the
tree is not entirely healthy, as indicated by the blackening of
the leaves. Any ideas what we can do?
The tree is in a sunny position, on slightly acid, clay soils.
The site is not waterlogged, as the tree is at the top of a bank,
adjacent to a pond.
A. I'd agree with you. Strawberry
trees are susceptible to "leaf spot" and it sounds quite
clearly that some infectious agent is responsible for what is happening.
I know of no case where plants lose leaves in the manner that you
describe by any normal means of dropping mature leaves.
I'd guess that the cause is bacterial similar to what happens
to roses with "black spot". The cure is not easy to administer
and the disease is quite resilient. The bacteria are usually spread
by water-borne rain-splash or insects. Not watering will help if
this is a contributory cause.
Remove all affected leaves and spray with Bordeaux mixture, remove
fallen diseased leaves from beneath the tree and dispose of by burning
or other means, but NOT on the compost heap. You may need to repeat
this treatment several times to eradiate the disease.
The other alternative is that the spots are fungal in origin,
in this case the spots appear to be concentric circles, close inspection
may show pin-prick sized fruiting bodies. The treatment is the same
but spray with benomyl or a copper-based fungicide.
Feedback - I didn't have enough Bordeaux mixture
to treat the tree when I looked in the shed, so I used a modern
systemic treatment that targets black spot. I used it at a fairly
high concentrations & drenched the entire tree, including all
the lower branches that had no leaves.. Within three or four days
a large number of 'budlets' have formed, even in those areas
which looked dead. So, I am going to repeat the treatment every
two weeks, which is the maximum rate that they recommend, although
I might reduce the concentration from now on.
I had almost given up hope, it looks like there may be a chance,
yet ( our gardener was full of doom about the prognosis! ). Thanks
for the help.... will keep you informed on progress.
Feedback 2 - I thought that I would give you an update
on our Strawberry Tree. Evidently, it is an Andrachnoides,
not Unedo, as I told you ( or so our gardener tells me).
Well, it was on the point of expiring, when I contacted you. You
suggested spraying with Bordeaux mixture, but I didn't have
enough - so I used Systhane from the Bio company. I have sprayed
at quite a high concentration, every three weeks. The results have
been really excellent. It seems to have stopped the fungus, are
whatever, in its tracks & the tree is shooting new, undamaged,
leaves throughout the branches. It really has been rescued 'in
the nick of time'. Thanks to your help, and a bit of serendipity,
it looks like it will be restored to full health...