Colletotrichum anthracnose

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Steph115
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Colletotrichum anthracnose

#1

Post by Steph115 »

I created a separate thread for this type of anthracnose because it sounds like it behaves differently. This may be old news to ya'll. Let me know if this should be combined with the existing anthracnose thread.

This is the pest that I believe plagued my first A. utahensis v. eborispina. I noticed the rings of spores forming near the base of the older leaves on the plant, following by increasingly rapid leaf retirement & eventual progression of the infection through the core. The ringed spores actually weren't obvious at first - it almost looked like the plant had sunburn near the bases of the leaves. Then the rings would appear after the leaves were completely done for. Below is a quote from the original description of Colletotrichum in A. utahensis by the Missouri Botanical Gardens:
In a short time many plants were found dying from a disease which first attacked the older leaves... The disease often has a striking appearance. The conidia of the fungus apparently germinate on the surface of the host and gain entrance through either the stomata or wounds. The tissues are penetrated by the mycelium in all directions, forming either a circular or elliptical spot which at first is darker in color than the adjacent tissues changing as the tissues die to either a brown or gray color. The adjacent tissues of the host under moist conditions turn brown and rot rapidly, the mycelium penetrating to all parts of the leaf
.

I recently acquired a larger A. utahensis v. eborispina with a small pup. I first noticed that the pup did not seem to be growing. The leaves of the core looked disproportionately small compared to the rest of the plant, but nothing else was amiss. Then I noticed the bleached, "sunburn" appearance near the base of some of the central leaves. In another few days, I noticed a small amount of brown liquid in the crown of the plant. It was on the top shelf and we had had no rain recently, so I figured something was up. The fluid was turbid & viscous when removed by a paper towel. Over the next day or so, there was obvious circumferential rot in the crown of the plant. I was able to remove the central leaves without any resistance whatsoever, and the entire core was mushy and rotted. The remaining leaves retired rapidly and the rings appeared (photo attached). I treated the plant with sulfur powder. I did not remove the pup because I wanted to disrupt the plant/spread spores as little as possible, as the mother plant appears to be doing very well without signs of infection. Also, a bulk of the infection appeared to be flush with the soil in the remaining crown of the plant and I fear doing more harm than good. So I dumped about a centimeter layer of sulfur powder in there and called it a day.

With some investigation, I identified the culprit as Colletotrichum anthracnose thanks to this tell-tale photo from the University of Arizona (pdf attached). Even more interesting, it sounds like this particular type of fungus primarily affects plants in cultivation & is particularly virulent in A. utahensis, as described by the Missouri Botanical Gardens (pdf attached).
The plants of the species A. Utahensis were the first to be diseased, and it is thought that the fungus was introduced into the greenhouse with this species. After a short time the disease spread to other species, none of which suffered so much as the original host.


This does appear to be fairly rampant among the A. utahensis I've seen in the nursery. I've only seen it in eborispina. The kaibabensis and nevadensis I have appear as yet unaffected.

Fortunately, the mother plant continues to have active growth without leaf retirement & no signs of infection. However I am very nervous & to be safe am planning on purchasing a copper fungicide ("Bordeaux Solution") which is what the authors recommend. Open to any suggestions ya'll might have. I know I probably need to remove the pup, but I'm just so scared to accidentally wound the mother plant or somehow promote the spread of infection. Maybe I'll remove it after treating?

A Disease of Cultivated Agaves due to Colletotrichum - Missouri Botanical Gardens

Problems and Pests of Agave, Aloe, Cactus, and Yucca - University of Arizona
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Viegener
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Re: Colletotrichum anthracnose

#2

Post by Viegener »

Ah, this happened to my Agave utahensis v. eborispina too. As I recall it was in the spring. What time of year was this?

I've decided not to grow any of the winter-dry agaves anymore. I love them all but the Southern California climate is not right for them. Gardeners here tend to have hubris because the climate is so good for so many plants, but not these...
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Steph115
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Re: Colletotrichum anthracnose

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Post by Steph115 »

Early-late summer for me. And I hear you - I'm starting to think that this may not be a good home for them either. I hope that I'm wrong though. These are my favorite agaves at the moment so I am going to see if I can treat them successfully & maybe even take them inside as others have suggested. I have a bright greenhouse window that should get enough sun and have lower humidity.

Otherwise, you know what they say... if you love something, set it free... :lol:
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Steph115
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Re: Colletotrichum anthracnose

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Post by Steph115 »

All right. I went ahead and treated all three by removing affected / retired leaves (leaving only the base/roots of the dead pup - painted all exposed surfaces with copper paste) and spraying well with copper fungicide. We'll see how this goes.
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Re: Colletotrichum anthracnose

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Post by Azuleja »

Good luck! I had no idea about that nasty fungus. Thanks for sharing what you learned. I have a couple recovering from a less severe infection. They seem okay but I think I'm going to overwinter them away from my main collection just in case.
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Re: Colletotrichum anthracnose

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Post by Steph115 »

Thanks Azul! And anytime. I hope you never have to know about this fungus! How are your utahensis doing?
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Re: Colletotrichum anthracnose

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Post by Stone Jaguar »

Steph:

Nice summary on this that should probably be dropped into relevant thread on this subforum?

As you can see, anthracnose is loosely used by a lot of people in horticulture as a catch-all term to identify certain types of leaf and stem blights caused by a half dozen or so genera of fungi. In this particular case, the authors of the papers you cite are referring to have positively identified the pathogen as one or more Colletorichum spp = a true anthracnose fungus.

Opinions vary as whether there are effective cures for anthracnose in evergreen ornamentals, with the body of evidence suggesting that suppression, rather than cure, is the best case scenario. Certainly you can control its spread with the right fungicides and improved environmental conditions. As I mentioned in the anthracnose thread here, my favorite "curative" (?) drench is Daconil (chlorothalonil) + Cleary's (thiophanate-methyl) at labeled rates. Please note that there are a number of states where these products are not labeled for non-professional use. IME, you cannot do much with severely impacted plants, but judicious leaf removal and treatment with a few fungicides labeled for anthracnose control are certainly helpful. I would also look to getting affected plant/s into a lighter, better drained mix once the disease spread has stopped.

I have been very fortunate with the handful of plants I have of the two eborispina clones I grow here. They get a lot of water during late spring, summer and early fall but are in an extremely bright spot under glass with excellent ventilation and planted in clay pots in ~75% pumice.

Good luck,

J
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Re: Colletotrichum anthracnose

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Post by Azuleja »

Steph, mine doesn't have any issues that I'm aware of. When I potted it, I added extra pumice to my normal agave mix, which is 55% inorganic. Hopefully it was enough.
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Re: Colletotrichum anthracnose

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Post by Steph115 »

Jag - thank you for your insights. I did read your thread on anthracnose and purchased Daconil in addition to the copper fungicide, with the potentially unrealistic the hope that since the mother plant isn't showing any signs of infection, I could avoid using the bigger gun if the copper controlled the colonization. However since I have it, I may opt for one drenching in an attempt to eradicate the soil of the pests in about a week or so. Regarding soil mixture: I did pot this plant up ever so slightly when I purchased it. However per others' experience with A. utahensis I attempted to disturb the roots as little as possible and simply added additional soil with a majority of perlite to the new pot. I think I will hold off on repotting unless I start to see them really go downhill.

Question for you about sun with these guys: you mention that you have yours in a very bright location. How bright is this? I had mine under my 40% shade cloth, partially because I thought my prior A. utahensis had succumbed in part to sunburn. However in hindsight I think the Colletotrichum was at fault the whole time. I'm wondering how much sun they can take in your experience. I've now moved them to my greenhouse window which is brighter and cooler, so hopefully less conducive to this pest in multiple ways.
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Re: Colletotrichum anthracnose

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Post by Stone Jaguar »

They will burn for sure if you're not careful. My under glass plants get full sun for most of the day all year long. Temps in that bay window almost always ~100 F during early afternoon for about half of the year, but with side panels open to permit airflow over the plants and plants sitting over humidity trays. Potted plant outside (colonial, not solitary) is fully exposed to sunshine from early morning through just after midday. As discussed in another post, I was rather surprised to see the leaf bases of these plants bleach almost to white earlier in the summer when first moved to a brighter spot. Much of the bleaching has since recovered, a few leaves did give up the ghost as the leaves constricted at burn sites.

I do acidify my irrigation water, add small amounts of encapsulated dolomite and gypsum to my soil mixes, and supplement feed CalMag at low rate (5 ml/gl) every fortnight or so during growing season...plants getting plenty of soluble micros while active. IME, this combo is particularly good to enhance color of glaucous/blue agaves and aloes.
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Steph115
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Re: Colletotrichum anthracnose

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Post by Steph115 »

Thanks so much for the tips Jag. I was also surprised about the leaf bleaching - I had no idea that's what was even going on until I posted photos here. None of my other agaves do anything even close to that. Good to know about the CalMag for blue/glaucous plants. I seem to acquire more and more of those =)
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Re: Colletotrichum anthracnose

#12

Post by Chimerico.AG »

Hello everyone,
I have the same problem on an A. Utahensis here in Italy. The fungus disease started to appear in the first days of spring, now I cutted a lot of leaves but there is still one single spot that is turning into a brown hole.
What do you think I can do?
Chlorothalonil products are now banned from the European community and for the thiophanate-methyl ones I need a card, so I'm asking if you've had any success with more common products like sulfur powder that is mentioned in the post or others.
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