| Q I
have a question regarding the side-effects of using an overconcentration of Physan on
my orchids. About a year ago, I treated my collection with a concentration of I tablespoon
per gallon of Physan. I have since learned that the proper mix is I teaspoon per gallon.
The plants showed no ill effects and, for the most part, have bloomed normally. This,
however is not true for my vandaceous plants. I have not had any successful bloom cycles
for any of these types of plants since the time I treated them. The bloom spikes will
begin normal development but as the buds are starting to get large enough to emerge from
the protective sheaths and.petioles, they blast and shrivel. It is possible that I am
wrong as to the cause, but the timing seems more than coincidence. Have you come across
any information or literature that may account for this with relation to the fungicides
and viricides contained in these products (RD20 and Physan)? If so, is this a permanent
mutation or just something the plants will have to grow out of their systems? A Physan and RD20 are names for exactly the same compound, largely quarterary ammonium chlorides, which are strong oxidizers. They are not systemic in any way, though if applied in too strong a concentration, they would certainly burn the plants. I think your symptoms may be coincidental, and sound much more like thrips to me. Thrips is commonly found on vandaceous orchids, and can only be controlled by dealing with it in the rest of your yard, as by the time it would cause damage to a flower spike, the damage would already be done. —Ned Nash. |
Reprinted, with permission, from "Orchids" - The Magazine of the American Orchid Society, May 2000.