Cactus blight - orange spots

[fyzygy]

A cutting I recently received was blemish-free, but in a matter of weeks developed a few orange spots. These seem to have progressively worsened (i.e. deepened), and spread. What is this plant disease? And what should be done to eradicate it? Thinking I should cut it right back. 

Edited January 15, 2023 by fyzygy

[Strontium Dawg]

Looks like phoma or anthracnose, neither of which is good news. They're aggressive and spread readily to other plants if left unchecked.

I'd quarantine it if you can nd commence weekly treatment with Yates antirot.

You might save it, but in my experience it's very difficult to eliminate once established, and I just bin affected plants now.

[fyzygy]

Thanks Glaukus. I've never come across this before. Yes, when I google images of those diseases, both can look similar to what I've got here. 

All of my incoming plants are loosely quarantined (separate pots, physically segregated from the collection). I actually got a few cuts from the same vendor, but it was just this one that showed symptoms. Lack of vitality first of all, followed by 1 or 2 orange surface spots that spread, and deepened over time. 

What I ended up doing was cutting the tip (about an inch above the highest blemish). Assuming new growth from base (i.e. pups) would also be infected. 

I'm guessing the potting medium should probably be destroyed, rather than recycled?

 

 

[Justler]

This blog from Darren at Herbalitics might shed some light on your situation: Mealy Bugs as a Vector of Trichocereus Disease.

 

The picture in that blog looks similar to yours and his observations point to root mealy bugs as a potential cause and focus for treatment. 

 

"Mealybugs are known to be vectors of fungal disease on other species, as they tap into a plants roots and suck out sugars, which invariably attracts fungi. So could this be the cause of this disease and could control of mealybugs be an effective treatment, if not a cure all, for some of these spotting diseases?" (Darren, Herbalitics)

Edited January 16, 2023 by Justler
Added quote

[fyzygy]

9 hours ago, Justler said:

This blog from Darren at Herbalitics might shed some light on your situation: Mealy Bugs as a Vector of Trichocereus Disease.

 

Thanks Justler. I had noted that page, but I'm not 100% positive it's the same thing. If you look at my picture, alongside the larger crater-shaped cankers, there's some smaller scabbing that more resembles the root-mealybug effect. Those smaller scabs aren't much of a concern, personally. The larger, deeper ones look (to me) qualitatively different. Heating the rootball to a specific temperature is beyond my capabilities, but I might devise a saponin drench as a precaution (I've got plenty of soap aloe to experiment with).

 

[jahliveforever]

Honestly wouldn't worry too much, spray with systematic fungicide followed by mancozeb and give it plenty of light and air circulation and it will heal up fine. Good tip is dont soak with water before a really hot day

[fyzygy]

Thanks jahliveforever. Mancozeb sounds ... positively evil. At least on Wikipedia:

 

A major toxicological concern is ethylenethiourea (ETU), an industrial contaminant and a breakdown product of mancozeb and other EBDC pesticides. It has potential to cause goiter, a condition in which the thyroid gland is enlarged and has produced birth defects and cancer in experimental animals. ETU has been classified as a probable human carcinogen by the EPA.^[5] Mancozeb has been shown to have significant negative effects on beneficial root fungi - totally preventing spore germination at levels far below recommended dosage levels.^[6]

 

 

[Justler]

11 hours ago, fyzygy said:

Thanks Justler. I had noted that page, but I'm not 100% positive it's the same thing. If you look at my picture, alongside the larger crater-shaped cankers, there's some smaller scabbing that more resembles the root-mealybug effect. Those smaller scabs aren't much of a concern, personally. The larger, deeper ones look (to me) qualitatively different. Heating the rootball to a specific temperature is beyond my capabilities, but I might devise a saponin drench as a precaution (I've got plenty of soap aloe to experiment with).

 

 

Ah, fair point. I had assumed it was the same disease/concern and the deeper ones were just in a worse state. 

 

Regarding heating the root ball, if you or a friend had a sous vide you could set up a water bath at exact temperature (46 degrees in the article) to simplify the process. Would be a bit more challenging without one though. All the best with it.

[fyzygy]

I inspected the roots, and everything looks ... healthy as.