I agree on the insecticides. But we do have one very nasty fungus running
around in south Florida that (without benefit of scientific evidence, just
based on personal experience) looks to me to have developed resistance.
Commonly called "Thai crud" and other nasty names. Symptoms are rough black
diamond-shaped lesions on foliage. Proper name appears to be either
Phyllosticta or Guignardia (depending on the stage in the life cycle??? --
that one boggles me). Primarily affects vandas. It used to be controllable
with Physan, now the only thing we have in the cabinet that will touch it is
Dithane M-45 (expensive and makes a big mess). So we rotate our fungicides
because we don't want anything else to become that nasty and hard to kill.

I am a firm believer in NOT doing preventive sprayings of insecticides,
but I have never heard of resistance buildup in lower life forms. My
understanding is that because they reproduce asexually, there is no
opportunity to pass on traits. Algae can reproduce sexually or
asexually, but I've not heard of a resistant strain...

For true. But for those with more plants than they can keep a close eye on,
or have room to space out properly (which I think is almost everyone here
G) ...
In fifteen years, I haven't seen any harm to plants from a monthly fungicide
spray (barring mixing/application errors). Kenni

Also keep in mind that good air flow around the plants is the number one,
best way to prevent fungal and bacterial infections.

"Kye" wrote in message
...
Wasn't there a thread AGES back about this being detrimental to the
general health of plants???