sometimes is not the easiest of places to grow herbs so I have been
most proud of my bay tree which has been battling the elements and
coming through with flying colours. However, I have noticed that
it has become ill. Of the three main branches, two have leaves on
it which seem to have paled. There are indistinct yellow splotches
(23 mm) covering the entire leaf except at the base which looks
normal. Some, but not all, have tiny black spots on them. Apart
from this, the plant overall is healthy and has a quantity of new
shoots emerging. I surmised that this could be one of a few things:
- A mineral deficiency.
In response to this I have been giving it feeds of worm liquid
- An infestation of
thrips or black spot?
- The cat has been
using it for oneses.
the Bay or Sweet Laurel (Laurus nobilis) should grow well
in Dunedin, as long as it is protected from frosts and strong winds.
It sounds like you have been doing all the right things if it has
been growing so well for so long. However, the symptoms you
describe suggest that all is not well with your bay tree.
I think it is unlikely that a mineral deficiency is causing the
problem, and your addition of worm liquid should deal with that
anyway. It is more likely to be a disease or insect pest.
I can think of several possibilities:
The first is an attack
from scale insects. They usually cause yellow blotches on
the leaves and stems and you see small brown, black or grey bumps
on the undersides of the leaves and stems. If there are only
a few, then gently wipe them off with a cloth or cotton bud dipped
in soapy water. Destroy any that you remove. If it is
a heavy infestation, then you could spray with white oil or an insecticide
which specifically targets scale.
Another possibility is
thrips, as you suggested. The symptoms don't quite sound like
thrips, which usually cause silvering of the leaves and leave their
"poos" behind as deposits on the leaves. Treatment is usually
by insecticide, such as carbaryl or diazinon.
leaves are caused by a disease. One possibility is mildew,
but this usually is visible as tiny grey threads. Treatment
is by an appropriate fungicide. There is also an algal leaf
spot, which is quite common in some native plants and will attack
bay trees. This is usually found in light-supressed plants,
so check that your bay tree is getting enough sun. It would
also be a good idea to make sure that your tree has good drainage
as bay laurels do not like wet feet.
Good luck with your tree,
and remember, if using sprays read the instructions and follow them,
and do not use any leaves from the tree for a period of time.
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