====== Rust Fungus (Anthracnose, Colletotrichum gloeosporioides) ======
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===== Description =====
Anthracnose is a fungal disease caused by the pathogen *Colletotrichum gloeosporioides*, commonly referred to by growers as "rust fungus." It causes localized lesions and rot on cacti, particularly under humid or wet conditions. While some plants can scab over and recover, severe infections can lead to progressive rot, making it a significant concern for collection management. It can also occur alongside pest infestations such as hard scale.

===== History & Origin =====
The identification of this pathogen on *Trichocereus* species is documented through community observations and expert diagnoses. The primary identification of *Colletotrichum gloeosporioides* in these discussions was provided by expert grower Gee Bee. It is a widespread fungal pathogen affecting various agricultural crops and ornamental plants, including cacti.

===== Cultivation Notes =====
Cultivation practices play a critical role in managing and preventing outbreaks:
* **Watering and Humidity:** Outbreaks are heavily driven by environmental factors, particularly heavy rain combined with heavy watering, which creates high humidity and saturated soil conditions. Rob Juterbock advises cutting back on watering intervals, noting that plants can grow out of the infection over time once environmental humidity decreases.
* **Surgical Excision:** Phil Mack suggests that for severe infections (where the tissue is actively rotting rather than scabbing), growers can cut the top 1 to 2 inches off the cactus. If the spots are already drying and turning tan, they are scabbing over and can be left to heal on their own.
* **Chemical Treatment Caution:** Michael Kießling warns that *Trichocereus* species are highly sensitive to sprays, which can cause severe phototoxic reactions and corking.

===== Community Discussion & Citations =====
//Analysis of the discussion.//

^ Date ^ Speaker ^ Confidence Score ^ Key Insight/Quote ^
| 2026-02-09 (approx) | Gee Bee | 10 | "#1 is anthracnose, Colletotrichum gloeosporioides. #3 is most likely Phomopsis/Phoma and 2 and 4 are unknown to me but fungal for sure. The biggest issue you have imho is the scale. That is a plague. Imidicloprid for the scale and various incantations and prayer offerings. Thiophanate methyl and Mancozeb for the anthracnose and Phoma/phomopsis, and the unknowns in 2 and 4 should also succumb to the Thiophanate and Mancozeb. But oh those hard scale." |
| 2026-04-27 (approx) | Gee Bee | 10 | "Anthracnose, Colletotrichum Gloeosporioidies" |
| 2026-03-02 (approx) | Tony Guajardo | 7 | "Did they start a color black, how much rain or watering has it had in the last 2 months and is it humid where you live? If so any of those might be the cause. I have over 600 cacti and this is pretty common for those reasons. I treat the with sulfur powder and the recovered just fine." |
| 2026-06-22 (approx) | Phil Mack | 6 | "Ok so you can cut the top or let it continue to turn gray. Think of it like a wound... its infected. Itll either heal itself and form a "scab" basically thatll look tan in color, which it looks like its already starting to do on one or 2 of them (edit:) or it will continue to rot." |
| 2026-04-27 (approx) | Rob Juterbock | 6 | "I've had this, I believe I saw it on mine after super heavy rain and before the rain I watered pretty heavy... most likely overwatered combined with environmental humidity. It grows out of it with time and cutting back on watering intervals" |
| 2026-02-16 (approx) | Michael Kießling | 7 | "Trichocereus plants are particularly sensitive to spray damage. Have you sprayed anything? I also had severe damage; they cause strong phototoxic reactions and corking." |

===== Credibility Notes =====
* **Gee Bee** is rated 10/10 as an expert override, providing precise scientific names (*Colletotrichum gloeosporioides*), specific chemical treatments (thiophanate-methyl, Mancozeb, propiconazole), and detailed pest identification (hard scale).
* **Tony Guajardo** is rated 7/10 due to his extensive cultivation experience (over 600 cacti) and consistent treatment advice.
* **Michael Kießling** is rated 7/10 as an experienced cultivator providing critical warnings regarding *Trichocereus* sensitivity to chemical sprays.
* **Phil Mack** and **Rob Juterbock** are rated 6/10 for providing detailed, practical observations on physical symptoms, scabbing, and environmental triggers that align with general botanical consensus.