Not too long ago, I posted some pictures of assorted plant discolorations and -figurations that were going on at work, and asked the internet in general for ideas about what was going on. Nothing clear emerged until very late in the game, where jean001, at Garden Web, said it looked like edema, which quickly became my favorite theory.
And then one of my co-workers talked to people from the plant diagnostic lab at Iowa State University (Ames, IA) and told me that they said it was probably mechanical damage, from being sprayed with pesticide right before shipping. Which was disappointing.
Well, I'm pleased to report that jean001 (and, to a lesser extent, I) has been vindicated: we received the official final report from Iowa State yesterday, and it reads, in part:
Microscopic examination revealed that the spots were caused by blistering of plant cells, not by damage from an insect or pathogen. We consulted with [redacted] and [redacted], both of whom said that the damage looked like edema, which is consistent with our microscopic observations. Edema occurs when plants take up more water than they can transpire through their leaves, and it can occur after humid, overcast weather, or occasionally in response to some chemicals.
So the official word from Iowa State is edema.
And this would be totally and completely awesome, if not for the fact that we have two new things going on now. One is, again, on a geranium, and my personal suspicion is, again, edema, though other theories have been proposed as well, some more far-fetched than others.
No insects, droppings, or webs were found on this leaf, nor do we have pest problems I'm aware of in the greenhouse except for fungus gnats and spider mites, and the spider mites are quite a ways away, as far as I've seen. Several of the geraniums in the general area of the one photographed are also doing this, but to a much lesser extent. General climate conditions recently: we've had a very springy spring so far, just like we had a pretty wintery winter. Occasional days with sun and highs in the 50s and 60s, but recently snow and upper 30s. It's been cold for the last couple days, which is a lot of why I suspect edema.
A second problem is on something completely different, which unfortunately I didn't bother to learn what plant we're talking about, but maybe it will suffice to say that the yellowing and bumpiness on the leaf in the center of the photo here is not how it's supposed to look. Again, no sign of bugs, and my tendency is to assume that we're overwatering, because there have been other plants that have had overwatering damage. (Catharanthus -- though nobody believes me when I say that's what it is -- and Ipomoea, as well as the Pelargonium addressed above. We're very worried about things drying out. More than we should be.) Though this is a different look, and so possibly a different problem.