Wednesday, July 27, 2011

Question for the Hive Mind: a Reader's Dieffenbachia

A reader e-mailed me to ask about a Dieffenbachia problem, which turned out to be something I hadn't seen before. Neither Google nor my books helped, and the few theories I came up with are mostly not borne out by the facts of the case, so I'm hoping someone out there has experience with this and can at least provide an ID, if not tell the person how to fix whatever it is.

The most alarming symptom is the weird bumpiness around the leaf midribs, often with a brown or tan slightly corky/woody top. This is reported on almost all the leaves, particularly the oldest ones, and are getting larger over time. It looks like the bumps mostly appear on the top of the leaf, but in at least one case, the reader provided a photo showing the woody/corky thing happening on the underside of the leaf too.

When I saw this initially, I thought maybe edema, or mechanical damage, but I couldn't find anything that talked about edema even happening on Dieffenbachia, much less an illustration of it, and anyway the environment would seem to be wrong for edema, since as far as I can tell, the environmental conditions are normal indoor temperatures and humidity.

My own plants have bumps like this on the midribs of some of the leaves, which I assume is mechanical damage of some kind (I've seen the same thing on my Anthurium "hookeri" and Zamioculcas zamiifolia), but in those cases, I already know the plant's been banged around a little, and the bumps are centered on the midribs and stems (particularly in spots where the leaf or stem has been bent, twisted, or stretched) and don't appear on other parts of the leaf. The reader says that the plant has not sustained any mechanical injuries while this has been happening, nor are there pets that might be causing this.

The reader also reports that the new growth is pale, yellowish, and sometimes shriveled, with margin burns on some of the leaves. (I didn't really see this in the photos, but bad-looking leaves could have been groomed off, I suppose.)

This has apparently been happening since spring, and is accelerating as it goes on.

There might be something like an insect or mite on the leaves, but it's hard to tell for sure; it could be dust or water spots. There's no webbing or stippling like one would expect from spider mites, and the specks don't look big enough to be aphids. The color and size is right for maybe an early mealybug infestation, but mealybugs don't cause leaf swelling and margin burn, in my experience. Thrips might leave streaky brown spots like this, but they wouldn't cause leaf swelling, and they're not known to be a particular problem for dieffs.

I did an on-line search for dieffenbachias with broad mites or cyclamen mites (which I at least know can cause weirdly distorted foliage and a dusty appearance), but didn't come up with anything there: if they infest dieffs, it must not happen very often. (Also, my understanding is that cyclamen/broad mite damage is mostly the result of the mites feeding on the foliage while it's still developing, not something they do to mature, developed leaves, as in this case.)

So I am stumped. Not only do I not know how to fix the problem, I don't even have any good theories about what the problem is. So I'm hoping someone else might have some theories. Even wild guesses would be better than nothing, at this point.

I asked the reader a few questions, hoping to find support for one of my theories (didn't get any), and the Q&A is below:


Has anything fallen on the plant within the last few months, or has the plant itself been knocked over?
NO. I really am careful with them and I learned to give them time alone :)

Do you have a cat that might like to bat at the leaves, or is there anything else in the house that might pull at or twist the leaves sometimes?
NO ...and I'm a dog person :)

Is it in a spot where a lot of people passing by the plant would brush up against it?
NO, it's on a shelf in a dead-end balcony.

Have you had the plant for a long time, or is it fairly new?
Fairly new, I think this is the second year I got it as a little-thin-young stem, and the first year it grew thicker and stronger after repotting the upper-stronger part of the original plant.

Has it been exposed to any extremes in temperature?
Yes, I think so. There were some days last month when temperature approached 40C - 104F, but the problems started before that.

Does it stay inside year-round, or do you put it outside for part of the year?
Only in the closed balcony. No low temperatures in the winter.

Do you leave windows open during part of the year, and if so are the windows screened?
Yes, but not wide open. There is only glass-filtered sun, and yes I use shades when sun gets too strong (3-4 hours in the second part of the day).

How long ago did you first notice it, and has it gotten worse, better, or stayed the same since then?
This sping. At first there were only few bumps and small. Now there are present on almost every leafs (especially the old and mature ones) and seem to grow steadily.
The general aspect of the plant is worsening. Leaves wither and partially coil, the color is paler and yellowish, and almost all old leaves developed on their brims yellow-brown dead areas. (see the pic in the message before).

My impression is that there is a systemic problem that affect the whole plant. Something metabolic. Coming from an infection or infestation or the soil.
I have to mention that I used universal solid fertilizer from COMPO. One stick, once (made in Germany).


Any of this ring any bells? Anybody?


Liza said...

Is it possible that there's more than one problem going on? Because yellow or shriveled new growth suggests overwatering to me. It may be unrelated to the weird bumps.

Outside of a strange water issue, I have no idea. I've never had a pest issue with Dieffenbachias, and I've never seen bumps like those.

I hope your reader continues to take photos and document what's going on, so others can learn from his plant.

Linda said...

My theory is that it's a combination of things, as Liza said.

Leaf margin burning could be indicative of fluoride damage, which Diefs are especially sensitive to. Looks like leaf tips may be burnt too, although hard to tell, but that's also a symptom. Didn't find anything listing lesions, scabs or corkiness on the midrib as a symptom though.

The pale and deformed new leaves probably indicate nutritional issues, I'm thinking something like B or K, since the overall color looks reasonable. Also didn't find much incriminating regarding the scabbing, although most of what's out there pertains to field crops, not tropicals grown indoors. This is where I'd start, though.

The plant looks stretched, indicating it's being grown in low light (this is coming from the perspective of a Floridian--we grow these things as outdoor landscape plants, so this may be typical of houseplant versions of Dief).

Justin said...

Where's Dr. House when you need him?!

Paul said...

Psyllid damage, maybe? That seems likely for a balcony plant and fits the damage description. I suggest a systemic pesticide. If it does nothing, the problem is viral or bacterial...pretty certain it's not a fungal issue, either.

mr_subjunctive said...


Certainly could be multiple problems at once, though my understanding is that the symptoms all started more or less at the same time, after about a year of normal health, so any theory would have to account for that.

Also, he tells me by e-mail "I trained myself not to act 'overprotecting'.
I tend to need to be around my plants every day to prone and water them, but I solved this urge by educating myself not to.
So, because I'm afraid to lose plants because of overloving (overwatering), my plants usually get water when the earth is really dry or even when they show signs of lacking the water.
That was also the case with dieffenbachia. She received for several months probably a little less water than she needed. Probably... not sure."

Liza and Linda:

Water quality could be part of it, though again, one has to explain why the same water wasn't a problem for a year before this. The reader says (by e-mail again) that he uses water from a public well for watering his plants, which is potable (also used by other people for drinking and cooking).


The growers' guide says that "lack of potassium tends to appear as necrotic lesions in the older foliage," which might fit. Boron not so much: "Lack of boron will appear as longitudinal ribbing in the new leaves -- without adequate boron the leaves have some difficulty unfurling."

I think it looks pretty healthy for an indoor plant, myself. Maybe a little stretched, but I've noticed that Dieffenbachia varieties that are in the same place inside vary in how stretched they look. I'm thinking that maybe some cultivars are just more prone to stretch than others.


Of course! It's lupus!

No, wait. . . .

Anonymous said...

What's the tall aloe like plant in the group shot? I've been looking for one for a while.

Aralia said...

Some pests can cause swelling like that when they suck the sap from the plant.

Carol Ann said...

When in doubt, repot. Yes, it could be a bug. Thrips and some mites can do a lot of damage with very few bugs. Could be a fungus. Dumping the plant out of its pot and examining its roots can tell you a lot. Trim any dead roots; if there are a lot of dead roots, repot in a smaller pot and water very carefully until the plant gets re-established. If there's no improvement, take a leaf to the local agricultural extension agent for a diagnosis.

Cris Bratu said...

Thank you all for your input! I will keep you posted on the progress.

Louise said...

Hi Guys,

Just discovered your thread whils looking for an answer to what I believe is the same problem.

I have just discovered lesions on the leaves of my Spathiphyllums. They seem to be focussed on the mid ribs near to the petioles.

On the top of the leaf the leisions are raised and dark green. More established lesions look to be turning a tan colour. On the underside of the leaf everything looks normal apart from the fact that the leaf dimples into the leisions.

Cutting the lesions apart there was no discolouration of the tissue inside and it was only a couple of times thicker than standard tissue. The tissue still seems to be functioning as generally, the infected leaves were all still green to the margins.

I have around 50 plants with about 40% of leaves are affected. The plants have been growing in the same conditions & location for a couple of years. I have only just noticed this issue now but it may have been around for a little while - with so many plants it wasn't obvious to see at first.

The spaths are planted in an internal greenwall - so the growing conditions are consistent all year.

Mechanical damage does not seem like a possibility as some of the plants are only accessible via a ladder and still affected.

I could see no evidence of any sort of pest on the leaves, stems or surrounds. The leaf tissue was not broken on the surface. The damage seemed to occur from within the plants but does seem to be spreading to other plants. Pathogen issue in soil?

About 5% of the Spath's leaves seem to be affected by fluoride/humidity issues but I could see no specific correlation between these issues.

Overall, the Spaths have been flowering for the last couple of months. Although they are holding their own they do not seem to be flourishing. There is new growth on some plants but not much.

I hope this helps someone to identify this issue for both myself & the original poster. Thanks