Yucca problem

[Gee.S]

The odd material on the Y. aloifolia is dry and brittle, and can peel off in sheets. I blast it off, and it's back thick as before within a day or two. The plant has been in a general state of malaise and declining. I have doused it a few times with insecticidal soap to no effect. Treated with imidacloprid to no effect, then with BT, which is definitely helping. BT treatment has been three weeks so far, we're not done yet. Has anyone seen this malady, and does it have a name?

Yuck 005.JPG (53.61 KiB) Viewed 4800 times

Yuck 002.JPG (69.89 KiB) Viewed 4800 times

[Laura81]

Have you tried a fungus spray?

[Gee.S]

No, not a fungus. All we usually have to do to stop fungal infections here in the desert is withhold water.

[Laura81]

It almost looks like a salt coating on it.

[Gee.S]

Not sure what it is. I haven't tasted it, but my guess is it would taste sweet. Ruth Bancroft Garden has also had some unpleasant experience with this malady; that was my source of recommended treatment. Unfortunately, they don't know which creature is responsible any more than I do. It had my Y. aloifolia in such a state that spider mites and aphids descended on the weakened plant, though they are now long gone.

[Gee.S]

For the final entry (hopefully) in this little saga, this odd malady seems to have been successfully beaten down. I had to remove the largest trunk, as it was preventing access to some small trunks that were harboring the pathogen. Once done, things turned around quickly, and I have seen no trace of the odd crystalline material in three weeks. Also, cores are now growing green and healthy once again.

On a more dire note to Agavephiles. I do believe several of my Agaves were also infected. All plants shown were within spitting distance of the afflicted Yucca. And though none showed any trace of the crystalline material, leaf damage is suspiciously similar. I assume the culprit is microscopic, I have still not seen hide nor hair.

Yucca damage

Yucca damage 001.JPG (83.26 KiB) Viewed 4768 times

Yucca damage

Yucca damage 002.JPG (77.03 KiB) Viewed 4768 times

Agave damage

Yucca damage 003.JPG (64.62 KiB) Viewed 4768 times

Agave damage

Yucca damage 004.JPG (108.97 KiB) Viewed 4768 times

Agave damage

Yucca damage 006.JPG (88.18 KiB) Viewed 4768 times

[Spination]

Thanks Ron for directing my attention to this interesting thread.

I just so far scratched the surface of the crystal mystery, but it would appear that one not unlikely possibility is that the crystals are Cacium Oxalate, and apparently plants have the ability to form them sometimes as a defense mechanism.

http://aob.oxfordjournals.org/content/88/3/387.full.pdf" onclick="window.open(this.href);return false;

Although the study linked may not be entirely applicable to the precise problem experienced, it does establish the idea that the crystals are a secretion of the plant, associated with a defense.

Although this study presupposes the crystal formation as a defense to herbivore grazing, I don't see why a similar mechanism couldn't be triggered by certain plant species in defense to an unseen pest such as the dreaded eriophyid mite.

I'm going to investigate this much more than the cursory searching done so far, but it will have to wait. I am computer/internet OD'd for today.

[mcvansoest]

If BT worked it must have been some kind of caterpillar or worm, because that is what BT treats for. I wonder if Spination has the crystal figured out - Agaves, Yuccas, and many cacti are known for calcium oxalate and oxalic acid as part of their defense mechanisms - it is what gives some people incredible skin reactions when exposed to Agave juice (me for example when dealing with the big weberi carcasses). I would not ingest it!

Could be that in the variegated Agave salmiana the damage was just that more extensive so as to not look similar? Or it is weakened because of it and gets some other affliction (any chance it was a little on the wet side?).

To me the damage on the agave and yucca leaves looks like spider mite damage, maybe exacerbated by whatever was afflicting the yucca that got killed by the BT. Not sure that BT would kill spider mites.

[Gee.S]

Must have been a very small worm, I never saw hide nor hair. I wonder if some manner of nematode was the culprit.

I sprayed the Yucca and all the neighboring plants with Avid and insecticidal soap. That cleared that aspect of this episode up pronto.

And no, the Agave was not on the wet side. It was getting fried like the rest of my Agavaceae charges.

[Agavemonger]

I have to agree with Mcvansoest; This looks like spider mite damage. I say it looks like it; not that that is necessarily what it is! Spider mites are usually more prevalent in greenhouse situations or low air movement situations. I wouldn't count out eriophyoid mites; they are quite fond of Yuccas. However, the damage on your Agaves doesn't look like mite damage. None of the damage looks like worm damage to me. Worms are easy to spot, and quickly get larger in most instances, plus they leave telltale droppings that are distinctive.

Take a real close look at the undersides of the leaves with a ten times lens and see if you see any pests; at least that is where I would be absolutely sure of first before I jump to other possibilities. It certainly looks like insect damage to me.

In some regards, this reminds me a lot of the problems The Killer was experiencing last winter. Daniel, does this look similar to you?

I should state that I am only discussing the spotting damage; the waxy exudate at the start of the post is something I don't recognize at all.

Oh, and Ron, what is "BT" ? Can't figure it out!

The Monger

[Gee.S]

Please read Post #5. Spider mites showed up, as did aphids. But these were scavengers that showed up after the kill, so to speak. So you guys are probably right, in that spider mites spread to adjoining Agaves rather than the primary pathogen.

Nematode worms would not be easy to spot, just a shot in the dark. Someone over at Bancroft must know what this is. I understand they lost a fair number of Yuccas to the same malady before a patron recognized it and steered them toward a cure.

BT = Bacillus thuringiensis.

[Spination]

So, now having spent hours looking for information or anyone's similar experience posted online, I now only have more questions that when I started.

In studying more about calcium oxalate, it appears that it's a crystal formation which forms INside the plant, so that doesn't sound right then looking at the pictures, unless it can be released somehow though cellular damage caused by mites, for example. And, these crystals deposits can be quite pervasive, in terms of the statement that the crystal can accrue up to 80% of the dry weight of the plant. In that case, it's not like it would be a tiny microscopic amount of crystal!

When I read the description, and viewed the pics, some key points were noted.
"dry and brittle, peel off in sheets...blast it off, and back thick within a day or two..." and that no insect was observed.
Regimens: Insecticidal soap, imidacloprid, and BT treatment "3 weeks so far".

Question 1... Is the crystal-like deposit from the plant, or from from another source? I think picture 1 is telling. In examining the clump of crystal in the center, it has the look of something that was exuded from the leaf, and the blob appears to have a coagulated appearance, and a "tail" underneath which seems to indicate solidification after from dripping from the main deposit. Right above the formation, the leaf itself has a patch with a ruptured look to it, and it appears the white deposit bled from that area, forming a crystal deposit that is seemingly mineralized. I did some reading too regarding "biomineralization" within plants (again - "withIN") Anyway, I feel like I answered my own question through examination of the photo, it looks to me like the deposit originated from inside the plant.
If so, then again it could anyway indicate a crystal structure such as calcium oxalate, as there are no other listed such crystalline structures visible associated with plant physiology. However, it would then be some sort of very rare event, as it does not seem to have been reported elsewhere online.
More on calcium oxalate
http://www.plantphysiology.org/content/124/3/1097.full" onclick="window.open(this.href);return false;
And plant Volatiles, released in response to insect feeding activity
http://www.plantphysiol.org/content/121/2/325.full" onclick="window.open(this.href);return false;

The only other possible white crystalline-like structures which have been associated with plants:

frost - easy to eliminate without consideration for obvious reasons

And (for the sake of levity), I can rule out certain visible surface crystals formed by certain plants since I'm sure your Yucca wasn't hybridized with cannabis. lol

Guttation - which can cause minerals left behind when fluids evaporate. Person described ""white deposits" "like perlite, crunchy" ???
http://www.walterreeves.com/gardening-q ... s-on-tips/" onclick="window.open(this.href);return false;

Deposits left from overhead irrigation, from "hard water". I'm dismissing that due to assumptions I'm making on the irrigation of your plants.

Sap, sugars from Yucca leaves? doubtful. Searching for all kinds of maladies concerning Yucca, I can find no other mention of any such occurrences.

Mealybugs - no insect activity perceived, and could they cause repeated deposits like that in a couple of days? Not likely.
http://www.gardeningknowhow.com/plant-p ... ontrol.htm" onclick="window.open(this.href);return false;

Powdery Mildew - "The fungus Oidium species causes the formation of a white, powdery growth or dry, brown, papery leaf spots. Initial infections usually come from fungi surviving in dead and decaying plant materials or from airborne spores from wild or cultivated hosts out-of-doors." Doesn't seem to fit the situation either.
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7493.html" onclick="window.open(this.href);return false;

Then, there is the question of the SUBSEQUENT leaf damage to the Yucca, and nearby agave - as in, 2 different problems. Hence, my 2nd question...Is the initial exuded material necessarily directly connected to subsequent leaf damage noted? Could the initial crystal deposit have been the result of a rare, but natural response to unseen mite activity, and the subsequent and similar looking leaf damage on all the plants in the area have been caused by the various treatments?
So, were the agaves situated nearby the Yucca treated as indicated (precaution?) in tandem?
The reasoning is simple. Could the "cure" have been part of the subsequently perceived damage to agave?
1. Insecticidal soap. 2. Imidacloprid 3. BT
That's a lot of "remedy" for a plant to deal with, whether there was an initial ailment or not, and couldn't all of that have an effect of the leaves?

Also, Bacillus thuringiensis, as a bacterial insecticide (and was it applied by overhead irrigation - and if so, was an adjuvant used?, or granular form treatment of the soil itself?) I guess I'm wondering what effect foliar applied bacterium would have on the plant itself, or if it's completely benign to the plant...and any effect an adjuvant might have had, if used. I did read "Bt is susceptible to degradation by sunlight" - could that cause any defect to the leaves?
http://www.ext.colostate.edu/pubs/insect/05556.html" onclick="window.open(this.href);return false;

So, I'm thinking along the lines that the Yucca could well have had a mite problem, for instance, but treatments of all the plants might have caused a subsequent similar noticed effect of all the treated plants. In conjunction to that, what possible effect the total combination of all those chemicals/treatments might have had on the plants as well.

As mentioned initially....more questions than answers. Missing is any analysis of the crystal-like substance. We can only guess from pictures.

I still can't believe I couldn't find one single other reference online to a similar event, the crystals are a mystery. I'm amazed you were actually able to find out the RBG had a similar problem. That they couldn't figure it out speaks volumes too (supporting the idea of a rare and unusual event).

[Gee.S]

Again, spider mites and aphids subsequently descended on the infested/weakened plant, causing the leaf damage. Please read Post #5.

I used BT (+ Spreader Sticker) weekly as a foliar spray. I also sprayed other Yuccas at risk (information provided by Ruth Bancroft, who also provided that the pathogen did not spread to any other plants in their collection, save aforementioned susceptible Yuccas), and adjacent Agaves for safe measure. It had an obvious if not immediate impact on the pathogen. Several weeks into treatment, it was gone -- until it returned in Spring because I hadn't sprayed the Yucca cores I could not see. Well before BT treatmnent, I applied imidacloprid (catchall), Insecticidal soap (aphids) and Avid (spider mites) -- once each. Avid is wicked effective on spider mites, which have attacked other Yuccas in my yard from time to time, particularly Y. rostrata. Crystalline material and general malaise continued without pause until subsequent BT treatment. The primary pathogen appeared to be restricted to the cores, as that is the only place the crystalline material appeared. So again, something very small. As I'm sure you know, Yucca cores are easy to infiltrate when compared to Agave cores. Just give one a slap to separate a core into 20-30 developing leaves. Did the same beastie destroy my salmiana variegate? No clue -- maybe, the two plants were in close proximity.

I suspect you're on the right track in regard to calcium oxalate, as evidenced by the impressive volume of material being produced both within and on the cores.

[Spination]

Right. I wasn't implying that aphids or spider mites were the problem, I got that. I was listing all the various things which I could find that could cause any kind of white buildup to appear on the leaves, and trying to apply a process of elimination. I felt that after the process, i was left where I started, as far as the possibility of calcium oxalate being the white substance.

As far as the leaf damage which became apparent later, my thinking on that split from there (appearance of white crust) regarding possible consequences of all the treatments.
So; Insecticidal Soap, Imidacloprid, Avid, Sticker Spreader, and BT. That's a lot of chemicals applied to all the plants in the immediate area of the affected Yucca, in presumably short succession. Did the agave plants pictured show any damage when you initially saw the apparent Yucca malady, or did the leaf damage on them appear afterwards subsequent to the various treatments?

The reason I mention it is because I see there is a one month lapse between the initial pictures of the Yucca, and the later pictures of the Yucca leaves, and the agaves. Clearly, there is a big difference between the Yucca leaves before and after, but I don't know if there was any visible situation with the agaves noticed before all the treatments were effected.

[Gee.S]

Agave damage came later from spider mites, and aphids in the case of the last pic. Leaf damage was not from chemical treatment, and was no worse at the time the second pic set was taken. This all went on for many months. I did not seek outside remedy until my own bag of chemical wonderment was exhausted. Had I not lucked upon a remedy, I'm sure the Yucca would have perished some time ago.

[Agavemonger]

Could the exudate be bleeding caused by Agave weevil larvae? Even though the beetles would most likely be inside the rhizomes or trunk area, sometimes plants bleed in other places when severely attacked! I know that these weevils actually seem to prefer Yuccas even over Agaves!

Also, I have had problems in the past with Imidacloprid being sprayed on plants. The chemical will severely burn Draceana cores, so much so that many of the leaves in the core burn, and hence many, many unfolding leaves have severely burned tips. It basically made the plants a mess for a year or so, and seemed to also affect their vigor. Brent Wigand showed me significant damage to many other plants at his home that seemed to have happened right after Imidacloprid use. We both are quite careful with concentration ratio control, so I don't think it was from using too much of the chemical. The Draceanas were on a side of the house that gets bright light but no direct sunlight. My other plants seemed unaffected.

Ron, were the Agave leaves burned on the afternoon sun side? Perhaps the combination of chemical residue and a bright (hot?) day caused the Imidacloprid to burn the plants.

Anyway, I have quit using Imidacloprid as a foliar spray. I guess I can use up the rest of it controlling ants under the benches.

The Monger

[Gee.S]

Imidacloprid was applied as a soil drench. I had never heard of it being used in any other manner. And this was months before learning of the BT cure.

And no, that is not burn. I live in AZ and know what burn looks like. Also, I have yet to lose a plant to Agave weevils (knock on wood). Leaf spotting/damage was from aphids and spider mites, as you had previously surmised. Always trust your first instinct.

[Gee.S]

I discovered the culprit for this infestation a few years ago (well, sort of...). The culprit was a small moth, no more than an inch across. More specifically, the moth's caterpillars, which, like the moths, are nocturnal. I went out with a flashlight sometime after midnight one evening, and found the Y. aloifolia in question covered in tiny little white inchworms. I did not see same anywhere else on my property. They were eradicated some 3-4 years ago, and have not returned.

[Meangreen94z]

Good to know. I’m growing a number of Yucca from seed right now. Including standard Aloifolia and the dwarf purple form.

[Gee.S]

If you ever see it, grab some BT. One issue that prolonged this thing was that I didn't stop to think (or read) that BT has a shelf life. So I was at times, using ineffective product.