bugs? fungus? eating my "orchid cactus"

Help, something is blistering my orchid cactus leaves. Picture is posted on alt.binaries.pictures.gardens. I've got two or three varieties of something Wife calls "orchid cactus" growing in the greenhouse. One (the most beautiful when it decides to bloom) has this blight that I can't seem to slow down. I don't want it to spread into the others until I learn something about control. Each little spot seems to start with a little watery blister, and then dry up into a much harder brown blister. I thought at first it was some kind of a bug inside the early stage blister. I popped one or two open and using a 10x glass looked for something squirming or with legs...... nothing I could identify. Is this ailment something anyone knows about? And also I'm sure that there is a better name for the plant than "orchid cactus"..... maybe some help there too!
Thanks in advance! Lynn (really rank amateur greenhouser)
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Your plants are epiphyllums, commonly known as orchid cacti. Your condition is rather common. While it could be caused by sucking insects, the spots are more commonly caused by either water left on the plants in full sun causing sunburn (water drops act as lenses magnifying the light to burn small round patches), or by overwatering at a time of the year when the temps are lower and the plant cannot use or get rid of excess water. Epiphyllums are rarely hit by fungi, at least on the "leaves" (stems). And the most common insect problem is mealybug which is easily seen. Give your plants a winter rest by reducing water and fertilizer especially if they're not in full sun or receiving full natural light, depending on your location. Good growing. Gary

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Thanks for all that good information. The overwatering and/or too much fertilizer is a condition that is quite possible. We used a LOT of water to keep the pot heavy enough to keep from falling off the shelf. Dumb, dumb, dumb gardening, I know...... perhaps lazy is also a factor. Thanks again! Lynn
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Water drops cannot act as a magnifying glass.
--

Travis in Shoreline (just North of Seattle) Washington
USDA Zone 8
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On Thu, 29 Dec 2005 08:09:48 GMT
[] ] ] Water drops cannot act as a magnifying glass. ]
Travis, you seem fond of unequivocal statements... I'm not sure if you're trolling or what, but a water drop certainly can act as a magnifying glass. Imagine the geometry of a drop, it's easy to see how it acts as a lens.
Don't take my word for it, google "water drop magnify physics" and follow any link, the first will do.
Just wanted to clear that up for anyone without a physics degree. :)
-E
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Emery Davis
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wrote:

Agreed, but one cannot burn the leaf or plant part it is resting on. It is far too close.
--

Travis in Shoreline (just North of Seattle) Washington
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wrote:

The water droplet myth explained so even those WITH a physics degree can understand ;) Still showing up in some popular garden literature is the notion that "day-watering" or water droplets can burn plants. The notion says that sunlight is "magnified by the water drop on the leaf to cause a leaf burn.
Anyone who ever burned ants, paper or anything else using a magnifying glass and the sun knows that the magnifying glass did not burn the ant if it were placed directly on the ant. Rather, it had to be held a distance (focal distance) from the ant to concentrate the sun's rays enough to burn the ant, paper, etc.
If this notion were true, all gardeners would cover all their plants prior to every rainstorm.
Farmers would not be able to prevent widespread "leafburn" after rain clouds gave way to sunshine. The root of this notion may have come from the effects of applying poor-quality water high in dissolved salts. As water drops evaporated from leaves,the salts left behind could cause a leaf burn. This will often happen if the water is from a tap hooked to a water softener system........and probably a lot of other reasons there would be high salt concentrations in the water that I'm sure if those who want to Google the hell out of the day, will be able to find.
The sun just came here Travis, wait 5 minutes and you'll probably get some too!
Val in Ballard (just south of Travis) Washington
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<snip>

It didn't last long.
--

Travis in Shoreline (just North of Seattle) Washington
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Sorry, Travis, but I partially disagree with you. While your general statement is true, there are specifics that can certainly vary. First, you do not have to be at the focal point for damage to occur, particularly over time. Heating of the tissue under the droplet can cause necrosis. Secondly, the water droplet may be almost spherical on hydrophobic waxy surfaces thus shortening the focal length. And thirdly, the thickness of the waxy layer can add more distance to the focal distance and in effect raise the focal point closer to the surface. While it's agreed that this is probably not the cause of this epiphyllum's problems, it's certainly not out of the realm of possibility, which you seem so certain of, for other cases. Gary
wrote:

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On Thu, 29 Dec 2005 08:09:48 GMT, "Travis M."
Nice to come back after a hiatus and find you still don't know shit from shinola!
http://www.google.com/search?hl=en&q=Water+drops+magnifying+glass
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wrote:

Water drops on a leaf for instance cannot magnify the suns rays and damage the leaf.
--

Travis in Shoreline (just North of Seattle) Washington
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Sounds like edema to me, and not unusual on thick-leaved plants. Check this out to see if this looks like your plant's problem: http://www.uwex.edu/ces/wihort/gardenfacts/XHT1116.pdf
Suzy O, Zone 5

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Thanks to everyone for all the help. This last one about edema, and the pictures on the "link" seem to fit quite well. I've pretty near stopped watering the one plant with the problem, and it has grown some new leaves (is that what they are called?) without the blistering. I'll try to be more aware in watering when it begins to heat up again here in NW Washington. Lynn

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