Quaternary amines, such as Physan, are strong detergents, which gives
them the ability to disintegrate cell membranes. The outer cell layers of
multicellular organisms, such as plants, have more resistance to this action than
single celled organisms, such as bacteria and fungi including single celled
spores. The use of quaternary amines against disease organisms depends on their
differential susceptibility to detergents, which means that it is indeed
concentration related. I have been using Physan at 2 tsp/gal for thirty years with
no problems; 2-4 drops/gal would be homeopathy, which very few plants
subscribe to. I use Physan particularly in conjunction with chemical fungicides; its
detergent properties help spread the fungicides evenly.
There are many applications for the disinfectant properties of quaternary
amines, which have little toxic effect on animals, and which give rise to
many trade names for equivalent substances. In addition to pool algaecide and
janitorial products, quaternary amines also find use to wash down dairy barns to
reduce the bacterial count in milk. Note the concentration in the particular
product you use for orchids. Physan and Consan are 20% solutions. Most pool
algicides are only 10% solutions, hence you might want to use such products
at 4 tsp/gal.
Bert Pressman
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the OrchidGuide Digest (OGD)
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