Dear Orchid Doc...Why is my Masd. Dropping Healthy Leaves?

[SFOS Web Administrator]

> In November purchased two new masd and placed them together, away from my original collection. In December I noticed that one of them had dropped a few of the healthy leaves. When I picked the pot up, more fell. Within 2-3 days it was completely leafless. The other that was sitting next to it didn't have any symptoms until a week later. Again it was dead within days. I had taken one of these into the greenhouse in which I had purchased it with the fallen leaves to try and diagnose this problem. They had no solution.
>
> Now, my local greenhouse had just brought in a new shipment from Hawaii in which I could not resist. I've purchased 7 of them and confined them to a different area. This time I used snail killer pellets, added only one pellet per pot. This morning I've noticed that my MASD. princeps is experiencing the same problem the other two had in December.
>
> This time I've taken a mixture of rubbing alcohol and ivory soap and spayed the plant.
>
> Is this snails? It it contagious? How do I protect the others?
>
> In my collection I have over 100 plants, 14 of which are Masdevallias.
>
> Please Help!
> Janine

Dear Janine:

This problem in Masdevallias is almost never the result of an insect
infestation, so your spray will not be any help. Usually this is a
cultural problem. You don't give any indication of your growing
conditions or the specific species/hybrids you are growing, so I will
have to give general advice. Extremes of temperature, often cold can
cause this kind of leaf drop. Though many Masdevallias are cool to
cold growers, not all are (you do mention princeps which prefers to be
on the cool end of the intermediate range). A few nights of extreme
cold can make leaves drop like this, usually a few days after the cold
snap. Staying too wet during cool periods can also do this. Although
there are fungal conditions that cause severe leaf drop like this they
would be easily diagnosed by the appearance of yellow margined black
spots prior to the leaf fall.

Conversely exposure to too warm a temperature range (especially in
conjunction with too low a humidity, and/or drying too much between
watering) can cause leaves to drop suddenly. I have had cold growing
Masdevallias begin to do this after spending too long a time in the
house (so I could enjoy the flowers), losing over half their leaves
within a few days

All is not lost however, as sometimes they can drop all their leaves
and if not kept too wet thereafter, can produce new leaves from the
rhizomes.

Even the "warmth tolerant" Masdevallia hybrids and warmer growing
species do need to have a sufficient temperature drop at night (10-15
degrees F.) to remain healthy. And they all are demanding of very good
air circulation and a minimum of 50% relative humidity. A couple of
other possibilities could be high ethylene levels in the greenhouse
from a dirty or poorly vented propane heater, or a leak in natural gas
lines.

Hope this helps,
Dennis