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Steve[_2_] · 01-11-2008, 02:21 AM posted to rec.gardens.orchids

wrote:
I have a Cattleya that I bought as a bare root plantlet almost 5 years
ago. It has taken
a long time to get going, but is now growing well and sending its
first flower shoot. It
was probably too dry and underfed in previous years, because it (along
with my phals)
has responded very well to finer bark medium and a heavier feeding
regime. I'm now
using 200 ppm N in a weekly soak with made with a 20-20-20 + trace
elements fertiliser.

One of the Cattleya's leaves is black at the tip and it's
progressing. There is now maybe
15 mm of dry black leaf at the tip and then a band of chlorosis of 3
or 4 mm wide. Can
anyone offer an educated gues on whether this is due to salinity, lack
of Ca, a virus, or
something else? The fertiliser I'm using doesn't contain Ca, but the
water is very hard,
containing an average of 276 ppm of total hardness as CaCO3 according
to the water
company.

Leo

It's not a virus.
Lack of Ca is unlikely with that water hardness. Low Ca usually shows up
as a dead spot near, but not at,the leaf tip. It shows up when the 2
halves of the leaf are still folded together, before the leaf opens up
flat. It usually starts growing bacteria which can kill the entire leaf
unless the bad part is cut off.
Salinity, or just too much fertilizer combined with the natural hardness
of the water could be the problem. This is not a problem I ever have to
deal with (super soft water here) but I believe it starts right at the
leaf tip on a leaf that is more mature than what I described above with
Ca deficiency.
What ever started it, it sounds like it now has a fungus working it's
way down the leaf. Cut off the bad part down past where it looks normal
and watch to be sure you stopped it.
Speaking of fungus, you described it as dry black, as opposed to wet and
rotted. That makes me picture antrhacnose. Anthracnose is more likely to
start at the leaf tips on thin leaved orchids like Oncidiums. Also it
usually starts out as spots and ends up dry tan/brown with a distinct
yellow line between the dead part and the green part. I'm not sure if
anthracnose affects Cattleyas but I sometimes have a Catt that gets a
dry brown leaf tip that may be it. I don't believe I've often seen dry
and black but sometimes I have.

Maybe something there will give you some ideas.

Steve in the Adirondacks