Agave edema

[Rob]

I read that at the agave summit 2, there was discussion on agave edema. Is there any correlation between edema and the mix materials? My east coast suppliers and I use a fair amount of bark in the mix and I am getting edema more than I use to on my A. americana medio picta alba as well as others and I am curious about others' experiences with the causes of edema.
Thanks,
Rob

[Tim Harvey]

I use a very lean mix of almost pure pumice, and experience it. Also plants bedded out in my pumice-amended clay soil get it too. Seems hard to correlate with growing medium.

T

[Allen Repashy]

It really doesn't seem to have a rhyme or reason to it..... hopefully with a lot of new feedback, and more testing by Matt, we can get to the bottom of it...

Rob..... Where did you READ about the Agave summit? I wasn't aware someone wrote about it

[Rob]

Hi Allen,
Tony Avent wrote a bit about it but with very little detail on the edema part. We have had an abnormally cool and wet summer and I think that has affected the succulents more than anything, It does seem that the A. americana medio picta alba has had more trouble than most of the other agaves we grow. Agave Joe hoak has also had lower leaf blocthes, circular, almost viral looking, but not quite. I have also had a lot of the more"blue patina" agaves have a lot of spotting in their color but not a lesion situation. This is based on plants under cover having no natural rainfall hitting them but subjected to higher levels of humidity and longer drying off times after watering.
Rob

[Allen Repashy]

I just discovered for the first time what some hard hail will do to an Agave. I have a hundred or so five gallon size plants that won't look respectable until they are 15 gallon size. kinda sucks when you have something ready to sell and don't want to grow it bigger.... There always seems to be some way for nature to remind us who is in charge......

[Matt Maggio]

First, let's not confuse correlation with causation.

Second, I'm convinced that edema, by its own description, does not account for all instances of related symptoms - namely sunken lesions, spotting, and in some cases, exudation of the cytosol (intracellular fluid) . My current theory on the cause of many of these symptoms involves a physiological disorder linked to photosynthesis. Many factors influence that process, soil properties and plant nutrition being no exception. Different soil textures, for example, can affect water relations with a plant. This in turn can affect stomata behavior, gas exchange, and therefore the efficiency of photosynthesis. Another thing that comes to mind: potassium is believed to be instrumental in the process of opening stomata - a potential link between nutrition and photosynthesis. My short answer is that soil properties, via their influence on photosynthesis, can enhance or detract from the severity of the disorder, but I see no root cause. I've seen agave cuttings with no roots and soil produce the same symptoms.

I'd be happy to explain my theory on this subject... but more tests are in order. Unfortunately, winter is the most difficult time to reproduce the symptoms during experiments because I have to battle cooler temperatures.

Matt

[Rob]

Hi Matt,
Thanks for the response. I assumed it was a multi- faceted problem and want to start narrowing down and changing the things that I can. It is frustrating and time consuming to grow from a pup to a 3-5 gallon plant only to have it the upper leaves have blemishes the season you try to sell it. I have not heard much on the nutrient requirements. Do you have any suggestions, bearing in mind that they are container grown in a northern climate?
Rob

[Matt Maggio]

Rob,

I'm no stranger to the feeling.

Concerning agave nutrition, I've stopped feeding for the winter here in Southern California, USDA Zone 9b. I won't resume again until days start averaging in the 70's or above, with nights above 45F. Sounds like you need to wait until the danger of frost has past. That should be close to when agaves start stirring.
Stick to a low nitrogen/high P-K formula such as 5-10-10 or 10-20-20. I'd been nursing a bag of Grow More 6-30-30. As a cautionary note, formulas such as these with high P often lack calcium and magnesium. This may be added by alternating with a fertilizer that contains such, bearing nitrogen levels and form in mind. The nitrate form is best, as opposed to ammonia, and should contribute 50% or greater of the total N. I had been alternating with a 13-2-13, containing 6% Ca and 3% Mg. You may also supplement with some gypsum and/or dolomite in the growing mix - test your irrigation water to see how much of these and other nutrients are already present. Agaves from limestone soils, such as A utahensis, seem to thrive best when copious amounts of calcium are added.

Matt

[Steve Steward]

Providing that drainage is good, I like to sprinkle in some kelp meal to most of my plants over the winter. The kelp protects roots some and decreases stress.

Steve

[Tim Harvey]

Steve, how does kelp meal protect roots, and what does it protect them against?

Curious,

T

[Rob]

Hi Tim,
It is interesting to hear that a pumice based mix yields the same results so that tends to lessen my medium theory. Matt, I just re-potted a lot of my smaller plants 3 weeks ago and all got 1 tablespoon of Osmocote 14-14-14, 3 month for a 6" pot. Given that they are greenhouse grown with a low of 55 degrees and a high that may reach the high 90s, they grow quite a bite over winter so I feel the need to feed. My water is high in pH, @ 7.9, much to the pain of my orchid crop. I get good growth with this system but still have the issues with tissue damage through out the year. I have increased air flow and plant hygiene and hope for better results. i will look furhter into the nutrient recommendations that you gave.
Thanks,
Rob

[Steve Steward]

Tim,

The kelp I use is something like 1-0-8 or 0-0-7 or close to one of those. The extra 'k' will decrease stress on roots, and promote at least some development when it's not too cold. Here in Tucson, our winters are generally mild to warm with short bursts of cold so my thinking is that any root protection will be good in conditions like that. I use it sparingly, and only in my potted plants.

There is also stuff about bioactivators in the kelp, but I'm not sure that does much in my cactus mixes that are lower in organics.

Steve

[Matt Maggio]

Ok,

I discovered this damage last week. The A. isthmensis and guadalajarana (first two) are from Poway, the titanota damage was noticed at Rancho Soledad. I know the plants in Poway had not been moved because they are mine. In addition, this happened in the outdoors. There was damage of the same age on other plants at both places... and a gang of usual suspects has emerged. As with a couple outdoor incidents last Fall/Winter, damage was most severe on guadalajarana, gypsophila, isthmensis, macroacantha, and many potatorum types. A pattern has also emerged with regards to the weather preceding obvious symptoms, in cases where the disorder has happened outdoors. Judging by the age of the latest symptoms, the damage coincided with an event spanning Thanksgiving day through the following weekend. In a period of three days, average daytime highs dropped between 20 and 30 degrees F throughout much of So Cal. Moreover, the San Diego region experienced a sudden onslaught of cloudy rainy weather, during daytime hours. I've ruled out heat stress because other heat sensitive plants nearby showed no stress. The damage had to have occurred because of the change. In Van Nuys, we had the drop in temps, but we were spared rain and overcast that Saturday. No damage to my agaves occurred in van Nuys... and I have many hundreds. In my observations last year the symptoms appeared after a sudden onslaught of cool cloudy weather. Therefore, I conclude that Climate Change is the likely culprit...
Seriously, I think that the sudden drop in temperature accompanied by lower light levels (clouds) is suddenly dropping the rate of photosynthesis...though I think light has more to do with it. With respects to light, a similar thing probably happens when a susceptible plant is suddenly moved into a dark enclosed space during the daytime. Again, I've had it happen under a wide range of temperatures. Why does the sudden drop in photosynthesis matter? For a CAM plant like an agave mild to warm temps should accompany the usual CAM cycle. I think a the amount of CO2 a plant takes in at night corresponds to how many "cylinders" it was firing on earlier in the day or the day before. In other words, there's a momentum. If the following day is much cloudier, or the inside of my van is much darker, the light energy required to run the Calvin Cycle in photosynthesis is reduced. The cycle slows, however, the release of CO2 gas inside the leaf from malic acid (CO2 concentrated in a solid/liquid?) occurs independently during the daytime. If this rate of release exceeds that which is being used in photosynthesis, excess CO2 gas could be building up within the leaf. Even though the weather is cooler and transpiration lower, I think the plant can't change its habit of closing stomata during the day quickly enough. The gas may just be trapped in the leaf because the stomata are shut, and the internal pressure may be enough to rupture the cells.

That's my current theory in a coconut shell. I think I'm going to take some agaves that had been used to mild sunny weather and stick them in dark refrigerator during daylight.

Matt

[agavegreg]

That's a lot to digest Matt. That's not fair, dredging up complicated topics from 30 years ago.

If I remember correctly, some Agaves can switch between CAM and C4? If so, are the ones that you have had the most trouble with only CAM, or do they switch depending on temperature and availability of water among other things. If that's the case, what mode were they in when the damage occurred?

[Matt Maggio]

I believe that the switching function is not species specific. Rather, it is a consequence of environmental factors such as temperature and soil moisture. I also believe that agaves switch to regular c3 photosynthesis. In fact, that's the pathway they really run on all the time after CO2 is realeased from malic acid. c4 photosynthesis is a separate adaptation on other plant families for hot, high light conditions. The cooler conditions that favor switching from CAM would not favor c4. I'll have to look into this further.

How do I know which mode? Excellent question. I'd have to observe the stomata under a microscope or submerge plants underwater to observe how many gas bubbles evolve from the plants. I can theorize because the plants had just emerged from warm temps in the 80s. I can also infer from studies done by Park S. Nobel on agave deserti that stomata closed during the day under similar temperatures. More experiments!!!

Matt

[Tim Harvey]

CO2 is pretty soluble in water, and is buffered by the bicarbonate ion system. I wonder how much a cell can cope with before it becomes a problem - could be quite a lot?

There is one straightforward experiment to try; pressurise a plant for a period then release that pressure rapidly. Same as a diver's bends - due to nitrogen bubble formation in that case. If you get similar looking damage then you know there's a connection.

I had plenty of Aloes show the same damage after the recent cooler weather, plus a few zapped by Mr. Frost himself.

T

[rpw]

Originally Posted by Rob

... Is there any correlation between edema and the mix materials? ... I am curious about others' experiences with the causes of edema.

That's a good question...

My understanding of edema is that it occurs when there is a sudden reduction in transpiration which creates an imbalance between water uptake and water loss with a subsequent overload of turgor pressure in leaf cells causing cells to burst and form water-soaked blisters. This can occur due to a closing of stomata caused by lack of sunlight from heavy overcast, or by a sudden change from warm dry air to cool moist air which drastically reduces the transpiration efficiency of the plant even if the stomata are open.

Actively growing plants are most likely to be affected, as are plants in warm moist soil. So back to the question about soil mix - how fast a mix drains and dries out can be a factor, as well as the time of year when plants are pushed with fertilizer. Anticipating a moist cold front and letting pots dry down to the wilting point in advance of the weather change, and avoiding watering during these times, may help to reduce the occurrence of edema in sensitive crops like geraniums for example.

But geraniums are easy compared to agaves - how does one wilt an agave? And would that work with an agave to prevent edema??
Most edema studies have been with commercial greenhouse crops and not with succulents or with CAM plants...
And what about plants that can switch CAM on and off, and do agaves do that???
In dicots edema is normally found on the lower leaf surface, but again agaves are different and show damage on both sides of the leaf.
And is this agave damage really just edema? It definitely looks like more than just edema, especially in Matt's photos...
Like Matt, I am not completely convinced, and it may be something more complex though edema or edema-causing conditions may be a factor...
I wonder if wild agaves ever exhibit the same damage - anyone know?

Peyton

P.S. The attached photo shows some damage on Aloe dichotoma caused by cool wet overcast conditions a month or two ago...

[agavegreg]

I have not seen the same damage on wild plants that I have had happen on my cultivated plants. The damage for me happens when I take plants indoors to give a talk, then back outside. They could be indoors for as little as 45-50 minutes, and they can show brown scarring the next day. It is not all plants and not all times of year. Plants kept dry show less damage than well watered plants.

Curiously, this does not seem to happen to plants being shipped through the mail.

[Matt Maggio]

Unfortunately, I've been thrown too many curve balls to be convinced that the problem is as easy as edema. Again, I've had occurrences on bareroot cuttings and drought stressed plants.
I'm passionate about solving this issue, and in that pursuit, appreciate all the observations from others on this forum. Keep the knowledge flowing.

Matt

[Boo Hollow]

Reading all of the environmental variables, they all point to fungal spore activation and resultant damage. The variation in leaf surface moisture coupled with temperature changes is ideal for fungal infections to set in as well as both viral and bacterial infections. The surface damage being present on the both the top and underside of leaves further supports that an external vs. internal causitive agent is at work.

The Agave edema theory begs one to ask the question, how does this occur with a plant's root uptake of water regualted by osmotic differential pressures. If a plant is "thirsty" due to higher differential pressure between the available soil water and the plant's needs, water is let into the root system. If the plant is turgid to capacity, the differential pressure is low and the rate of water flux it therefore low. Although there are plants that have been reported to suffer from over consumption of water to the point of bursting, I cannot find any references that link plants in the Lilaceae family to having this problem. At least not readily documented. It would take some funky activities for the cell wall to allow excess moisture to accumulate to the point of rupture. Has anyone considered that the temperature near the ground may become colder then the ambient and actually reach a freezing point? It does not take much for water to start expanding (ice formation being the worst case) as water is densest a bit above freezing and once below that point, it starts to reorder and expand as it crystalizes. The rapidity of the cell wall damage is what is perplexing.

For those whom might really want to answer the problem, Ann Chase at Chase Horticultural Research accepts samples for diagnosis (although it costs a bit). Maybe a collection amongst the Forum members to fund an analysis??? Allen could be the treasurer to fund the research. Any ideas???

[sroberts]

Hi all,

Although I live in Modesto in central California, I lived by Morro Bay for a couple of years and moved back to Modesto in July of 2009.

I loaded up about half of my plants in a U-Haul and they were in there from late afternoon till early afternoon the next day. I unloaded them into my backyard under a shade tree until I could get some shade cloth up about a week later.

3 or 4 days after their U-Haul trip many of my Agave plants had the markings like what's seen in post #13. Naturally I was devastated. I never knew what caused this but just assumed they stressed out on the move and the hotter climate in the central valley.

All of the plants have new good growth on them now but it will take a few years to grow all the bad leaves out.

Interesting reading on this topic!

Steve

[Matt Maggio]

Boo,

That won't be necessary... in so far as disease diagnosis is concerned. The problem is incontrovertibly abiotic. If you don't believe me, take a few Aloes or Agaves and place them in a dark room or in a vehicle from late morning to early afternoon, not overnight. You can do this on cool or warm day, in fact you may even leave the AC on or the windows cracked... it's not the heat that matters AS MUCH as the darkness (or poor light quality) and somewhat stagnant conditions. Don't wait until winter because you're less likely to induce the disorder at that time. Perform some experiments like this, then tell us what you observe.

I'm not trying to be condescending because it seems you haven't encountered this problem before. I don't pretend to have all the answers on this matter, but have countless observations under a variety of environmental conditions coupled with strong knowledge of plant physiology. Literature in direct reference to this disorder is pretty much nonexistent for the same reason literature on nutrient disorders of succulents is lacking - the plants we're dealing with are just not of that much economic importance - no offense to all the growers out there. The only thing that comes close to the subject is a few paragraphs on the San Marcos Grower's website. Heck, not even the gentleman who "wrote the book" on the physiology of CAM plants, Dr. Park S. Nobel, knew about this disorder when I asked him. However, after explaining to him the same theory as my earlier post, he thinks my theory is quite plausible.

Again, I believe the problem has to do with gas exerting internal pressure, the source of which being trapped CO2 Gas stored in cells as Malate from the previous night's "dark reactions" (Agaves and Aloes being CAM plants). When the plants are placed in conditions of poor light quality and air circulation the next day, the rate of photosynthesis and gas diffusion into the atmosphere drops dramatically, while the CO2 that gets released within cells as a result of PEP carboxylase enzyme activity on malate builds up. This enzyme activity, as DR. Nobel has told me directly, can in fact occur in a circadian rhythm fashion independently of its use in the light dependent reactions that would otherwise fix the CO2 back into sugars. Furthermore, if this were simply a fluid turgor pressure issue, I would not be observing the same symptoms on both wet plants, dry plants, and bareroot cuttings. Finally here, I think that the leaf morphology of succulent monocots doesn't aid matters. One finds a thick, waxy cuticle atop a spongy mesophyll, which allows the gas to become more easily trapped.

Also, you're less likely to induce the disorder in winter because agaves and aloes can switch to normal C3 photsynthesis under prolonged periods of cool humid weather. This would place the stomata open during the daylight hours, allowing gas to vent. Interestingly, the problem can occur in winter when the weather fluctuates wildly between warm - Santa Ana wind conditions as they're known in SoCal - and cool damp conditions. This probably goes back to the plants having a circadian rhythm, and being "confused" by the sudden changes from warm sunny to cool cloudy. You'll notice that agaves and aloes mostly inhabit climates that are more stable from day to day (not necessarily from day to night), and aren't really subjected in nature to sudden hot drying winds following cool cloudy weather. One exception would be the Berg winds in some Aloe habitat of South Africa, but those habitat plants are in the ground. We should compare plants in the ground to plants in the ground... lookin' like a fool with your plants in the ground

Assuming all the above were not the case, both the timing and nature of observable symptoms rule out any pathogen. There are a whole host of reasons, no pun intended, but I'll only name a few. Most pathogenic fungi for one require free moisture on the leaves for at least several hours for the spores to germinate and infect the tissue, only then does the damage become visible days later. The symptoms we're concerned with can easily become visible in 45 minutes, and one can sometimes see cytoplasm bubbling from the stomata pores. Under no circumstance were the plants wet on the leaf surfaces. Secondly, there is no rot or blackened tissue, only sunken water-soaked lesions that become dry and necrotic in about a week. Finally, foliar disease symptoms will usually be more random over an entire plant. These symptoms have a peculiar pattern. They usually occur on newly matured leaves, beginning a third of the way down from the leaf tip.

Matt

[agavegreg]

About 2 weeks ago, Mark from B&B Cactus in Tucson went over to So Cal and picked up some agaves among other things. He sprayed the agaves with an anti-transpirant before putting them in the van and heading back to Tucson. None of the agaves showed the type of damage normally expected in a situation like that.

[Boo Hollow]

Originally Posted by Matt Maggio

Boo,

That won't be necessary... in so far as disease diagnosis is concerned. The problem is incontrovertibly abiotic. Matt

Matt - Thanks for the extended explanation. What I find/found perplexing was the differential water pressure resulting in the cell wall rupture in the Agaves. So I would assume the physiologic damage would be where the root pressure and transpirational pressue exceeds the capability/capacity of the stomatal openings and although the guard cells open up wider under increased water pressure (stomatal pore opening to allow transpiration) that they just cannot allow sufficient water to escape to relieve the rapid pressure buildup within the cells?? It is readily apparent in leaves with thin cross sections, but the thicker cuticle and leaf structure of the agaves is where I get lost.

I had sent a note to Park and am looking forward to his reponse. He is out of the country until October 4, but it shows he did read my email this morning. I am hoping that he has some more recent info that may not yet be published.

Regarding whether or not the surface of the leaf is wet or not, I would tend to think that since there is a differential temperature between the leaves and the surrounding environment, especially when placed within let's say a car trunk, that this cause surface condensation and physiosorbtion of available air moisture, which is really all it takes for a fungal infection to acheive the right temp and moisture levels of sporulation to occur. My experience, albeit limited in fungal pathology, is that the fungal growth can be readily in progress well before any readily visibile (with the naked eye) indications of its presence are detected and soon after optimized conditions present themselves, does one see the bloom or apparent damage.

In getting back to my original response that it is not a sunburn response, I still stand by that conclusion. Whether the damage is abiotic or not is the question. The darkening of the tissues to a black state is what is most perplexing within the short time duration from initiation to detection, and is why I would think it to be more a biotic response vs. purely physiological response. Your thoughts on this discoloration would be appreciated. All of the photographs of Oedema (Edema) show light brown to rustly pustules and none of them show the dark brown and black tissue coloration.

[Matt Maggio]

These are my most recent and compelling examples of the Monocot disorder. The damage is about three months old and occurred while these plants were kept inside a dimly lit room for several daylight hours during a plant show(I have witnesses). I would be interested to hear from anyone who has had this happen to their show plants while on display in similar environments.

Notice the dark patches... my best explanation is that these are tannin precipitates which form after the cell vacuoles have emptied their contents. The damage usually shows-up white to cream-colored before progressing to darker tones.

I don't think root pressure is a key parameter here. I think the pressure is originating internally within the cells, for the reasons I explained concerning CAM photosynthesis. Now, why in doesn't one usually see this disorder on plants with thin leaves where one might expect? It is because, in my view, that most plants with thin leaves are not CAM plants. However, most thin leaved bromeliads are. I have had this disorder occur on Aechmea and Neoregelia, both under conditions of transport during the day. So, I think being a CAM plant is the first problem. The second is having a thick waxy cuticle, which works fine for trapping moisture, but is not so good for allowing gas to escape when needed most... better reach for the Beano Third, it is my knowledge that increased CO2 concentration within the leaf can trigger the stomata to close(stay closed in this case). It's the plant's way of saying... "when". But this could compound the problem. Tim Harvey pointed out to me that the plants have a bicarbonate buffering system within the cytoplasm that should absorb some of the gaseous CO2, but this could be getting overloaded.

Greg - it's interesting that an anti-transpirant was involved in the case you mentioned. I would need to know more... what time of day was it for instance?

I welcome everyone's comments and critiques on this subject. I'm as determined to reach the bottom of this as anyone else!

Matt