live in Te Horo about 60 km north of Wellington. The weather has
been wet and humid over the last few weeks. I have four long lines
of silver birch trees bordering a driveway about 40 of them.
They are dropping lots of leaves and the leaves are yellowed with
brown spots rather like the black spot infecting my roses. Is this
a blight? It's not very practical to spray as they are very tall
and large, well-established trees.
birches tend to be as tough as old boots. They do, however, get
a leaf spot disease a lot like the symptoms you describe, but this
usually occurs in autumn when they are supposed to lose their leaves,
and it does them little harm. It sounds like the wet weather has
caused a disease outbreak and the leaf-drop.
Perhaps the trees are
not completely happy? While silver birches usually do well in either
wet or dry soils, a sudden change, perhaps due to lack of drainage,
could trigger an attack.
As you say, spraying
is not very practical, but you could reduce the amount of fungal
spores present in the area by removing dead leaves and branches
from around your trees. You could also get an arborist to carefully
prune your trees to let a little more airflow occur.
by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor
of Resource Management.
with permission from NZOOM Home and Garden content,
from the previous
The views expressed here are not necessarily those of the RNZIH