Bruce Musgrove wrote:
I spotted this on one of my orchids while watering them and was wondering
what it was.

First, it is a dead leaf. No seriously, cut it off as close to the
plant as you can. If it is infecting the plant you want to remove it
with a quickness to keep it from the heart of the plant. A small pin
hole or crack in the leaf can absorb and transport the chemical
treatment. It looked as if the plant tried to seal off the damaged
area, but failed. If it (the plant) perceives it as a threat, it will
abort the entire leaf. How long have you had this orchid? If it was a
recent acquisition there may have been some physical damage that you
were unaware. Plants from department stores and resellers get handled
a lot, often by people that don't know or care.

Could this be a burn mark from water sitting on the leaf in
the sun?

Probably. When the leaves fall in my area, it changes the light
intensity through the sunny windows. A drop of water, in this case oil
from the soap will scald the leaves because it acts like a lens and
concentrates the light more. When the water evaporates it will leave a
drop of the pure soap. It will also conduct heat and cold more.

I did spray with Safer brand inseciticidal soap last week at the
end of the day. Maybe I put it back in the window to soon?

Why? Did you have an infestation? If so what was the pest?

You really have to watch oil based products when spraying. Some
products shouldn't be used on orchids at all, or used at a reduced
concentration. Even pure neem recommends a balance of detergent in the
mix to keep the oil in solution. Keep it stirred or shake the sprayer
to prevent it from separating. Don't spray all the way to the bottom
of the bottle. If it separates, there is too high a concentration at
the bottom of the sprayer. That applies to poorly dissolved plant food
that settles.

I looked in the Ortho books and could not find anything similar.

Ortho is selling chemicals. They won't show damage caused by improper
use. Not to say you didn't follow the instructions and have good
intentions, just that their products may not be tested on or
recommended for orchids, maybe that particular orchid was more
sensitive than your others, or the concentration changed as you
sprayed.

Honestly, if you can find an orchid society in your area, you may want
to do so. They can be a lot of fun and an amazing source of
information. Keep in mind, they aren't A.A. They are enablers,
everyone will have something different, and you will want more for
yourself. If the members can agree on an order, the group discounts
from growers' catalogs can be a benefit plus the larger the order the
more balanced the cost of shipping.

Orchids at box stores get handled a lot. They are packed, shipped,
distributed, shipped again. Unpacked and put on shelves with other
tropicals or outside in garden departments. Employees and customers
handle them. They may be inappropriately potted and incorrectly
watered. The staff may or may not be knowledgeable, more than likely
not. You have to look at the plant carefully, not just the blooms. It
may take years for a Catt, Onc, or Den to "outgrow" the damage. Phals,
because of their monopodial growth may NEVER recover.

However most of the purchases are impulse. Why did you buy it,
"Because it was there, pretty, and I had $15, or it was marked down
because the blooms had faded, the plant looked healthy, and I have
time." Been there, done that, and sometimes still do it. Everyone
starts someplace.

Best wishes, Happy growing