Yellow Spots forming on Myrtillocacti

[Saguaro123]

I noticed these yellowish-orange spots forming on my Myrtillocacti during the past week. The spots are not mushy. I think it's because of the cold weather, as our nightly lows have been in the mid to upper 30s. However, my understanding of most Myrtillocacti is that they're hardy to the mid 20s (please correct me if I'm wrong.)

Are the spots something I should worry about? Is there a way to stop them from forming and spreading? The first plant is a short spined form of M. cochal and the other is a monstrose form of M. geometrizans

[tumamoc]

Looks like spider mites damage
spider mites

[iann]

Lows in the upper 30's indoors? Myrtillocactus may be hardy to the mid 20s (or they may not!), but that would be in arid conditions for a very brief period with considerably warmer days. I think mature plants are also more resilient to freezing, young ones not so much. In more humid conditions, or simply because Myrtillocactus are not that hardy, orange or brown patches can be formed in the cold. That could be what you're seeing if they suddenly showed up after a cold night or two (or even a few weeks later).

I don't think this is mite damage. That tends to be more widespread and with a mottled appearance, eventually merging to wider areas of scarring, not forming in somewhat isolated patches like this.

[Saguaro123]

Lows in the upper 30's indoors? Myrtillocactus may be hardy to the mid 20s (or they may not!)

The myrtillocacti were outside in a shaded patio and protected from the rain. Then, they were brought into the garage after observing the orange spots. I think it's because of the cold weather because they were outside when our nightly lows started to drop. However, I should also check if any spider mites are present.

The orange spots stopped forming on the M. 'fukurokuryuzinboku,' but the orange spots on the M. cochal are continuing to grow. Would it eventually turn into rot, or would they harden and turn brown after giving it more warmth?

[Ksenija87]

Hi Saguaro,

I don't know the english name of it, but from the symptoms I think it could be Elmintosporiosi (that's the italian name of it ). It's a micromushroom that infects the cacti at a temperature between 16-30°C (= 60-86 F), especially when cacti are all very close in a same closed area (like your balcony, if I understood it right). Anyway: to be 100% sure, I suggest you to find one of these products and spary the cactus but more important the soil all around:

Mancozeb, chinosol, captan

Let me know if you've troble finding these, and I'll ask my father for the name of the main active principles, so the main stuff that makes things work
My bests!
Francesca

[Saguaro123]

Hello Francesca,

I don't think there's a name for the fungus in English, but it is from the genus helminthosporium. I figured it was a fungal infection because the spots on the monstrose form seem to match the symptoms of various spot leaf diseases caused by fungi. I'll go to my local hardware store tomorrow to see if they sell any of the fungicides listed.

Thank you so much for your diagnosis!

Regards,
Byron

[Ksenija87]

Hi Byron, you're very welcome! Let's stay updated on the fungicides-search.
My bests!

Francesca

[Saguaro123]

I was not able to find the fungicides listed at the local hardware store, so I decided to go with a bottle of Neem Oil extract. I applied it on the Myrtillocacti yesterday, and I hope it works. It probably takes a week to see if the fungicide cured the fungal infection, right?

[Ksenija87]

Exactly, with natural products it takes a little longer. No surprise you didn't find them. The active principle is anyway manganese ethylenebis(dithiocarbamate) (polymeric) complex with zinc salt. So basically manganese+zinc salt. It could also be possible that the US have forbidden the product because it's highly toxic (sadly like every pesticide). I must say the manncozeb family (including the other two I mentioned you) is very effective. You can also simply try a powder mixture of verdigris and a dash of additional sulphur to be spread on the soil. It's always a simply and almost natural way to disinfect the soil, but it should be repeated at least once a week for problems like yours.
How many degrees do you have now?
My bests! Francesca

[greenknight]

Fungicides only prevent fungal infections, they don't cure them. If it is a fungus, it might stop any new spots from forming.

Helminthosporium would turn dark and rot within a few days. If that's not happening, most likely it's just scabs caused by cold, humid conditions. Some species are prone to that, but it's only a cosmetic problem.

[Saguaro123]

How many degrees do you have now?

Our daily highs have been anywhere between 50 and 60 degrees Fahrenheit while our nightly lows have been below freezing on a clear night to about 45 degrees Fahrenheit when it's cloudy or raining.

The yellow spots are starting to harden, so I guess that's a sign that the fungicide is working. It is possible that there's no fungus to begin with though.

[Pushrestart]

Want to add my Myrtillocacti was doing something similar I included some photos in my thread, I honestly have kept it isolated and will try to withhold water till Spring. I believe it is some kind of opportunistic fungi as the yellowed areas are sunken in and tough meanwhile the rest of the plant is somewhat squishy but not soft or rotting. My concern is the 'white-ish' rings. Its also very hard to properly treat something like this in the winter since watering should be kept to bare minimums and being outdoors and spraying toxic chemicals is difficult.
http://www.cactiguide.com/forum/viewtop ... 24&t=36591" onclick="window.open(this.href);return false;

[Ksenija87]

Sorry for late answer, busy days at work
@Spence: everyone has its method, of course. When I see something weirdo going on (like fungi or cochineal), I like to disinfect the soil, that may carry some bacteria inside. I don't think it damages the cacti, it's a sort of prevention against a bigger spreading of the
@Byron: it's definitely working. From the temperature I'm more and more convinced it's elmintosporiosi. Keep anyway an eye on your Myrtillocacti, to ensure that the spots don't become soft and spongy. In that case, it means it's rotting.
@Pushreaster: hi, I suppose you have the same disease on your cacti like Spence's. Since he's having good results with Neem oil, you could try that on you M. too. As I previously said, I like in these cases to disinfect the soil with verdigris or with some fungicides (the list it's up above, in some posts). They contain as active principle manganese ethylenebis( dithiocarbamate) (polymeric) complex with zinc salt, even though I know Spence couldn't find any of them.
Bests guys!
Francesca