Recurring black spots on Cattleya x Pot cross

[Skippersmom]

My location = ‘high plains’ USA. My orchids are outside May through October. Inside through the winter. I have several other Cattleyas that seem to do well, grow, flower, etc. They do not have the issues I describe below.

C. Sierra ‘LittleRiver’x Pot. Winners Circle x Pot. Ryo Iwata.

Gifted to me Oct. 2022. Blooms has wilted b4 my friend could get the plant to me. Popped up another flower around Jan/Feb. Seemed to be happy, doing great for several months thereafter.

Late spring 2023 it went out to the ‘cabana’. It shot up a new Vigorous pseudobulb/leaf. Suddenly started blackening at the tip moving down. [Pic 1] Thought it might be fungus, so treated w/ Cosan. The blackening was rapidly aggressive and I finally cut everything off before the black reached the rhizome.

Decided that if this was fungus (and since the rest of the plant seemed o.k.),… I pulled it out from the medium + sprayed everything w/ Cosan, [again] + and plopped into water for a couple weeks.

All good; happily it began to grow 3 new leaders. [Pics 2 & 3]. Now placed in new medium and pot. It has stayed indoors w/ indirect south exposure.

Around that time, researching this led me to consider that instead of black rot, that this could be Ca++ deficiency. One recommendation I found was for CAL-i-MAGic. So, that fall 2023, I also began once a month treatments with CAL-i-MAGic for several months. May-June-July, those leaders developed but were a little stunted/short. 2 actually bloomed (a single blossom). The 3rd one was stunted and started developing black at the tip & patchy throughout the leaf and pseudobulb. [pics 4&5]
(I had cut-back on the Ca++ supplement about April).

So the last 2 months I resumed the CALiMAGic and also sprayed again for fungus.
Fertilizer = RePotMe slow release granules since I got it. Weekly watering sessions = are rotated with CaliMAGic or ¼ strength balanced fertilizer or Superthrive.

About this time of year, I hit every plant, especially the ones that have been outdoors, with QuantumOrchid monthly.
So now this orchid –
*remains in the same pot,
*The bad stuff cut back and sealed,
* Has new shoots coming out,
*None of the original old pseudobulbs & leaves have this issue.

IF this is a Ca++ deficiency, then I could use help understanding how to better use the supplement. If this is something else, I appreciate guidance. This orchid is a fighter.
Thank you in advance for your thoughts and sharing your wisdom.

[estación seca]

Blackening Cattleya shoots are usually caused by too little water, insufficient calcium or too much sun. You won't have rot on Cattleyas unless your relative humidity is very high. Fungicides are rarely needed.

You're probably providing enough calcium. The plant is vigorous, and trying to grow. I think your problem is a combination of too much sun and not enough water. The roots with ring deformities could be thrips insect damage.

[Skippersmom]

Thank you for your reply.
Just for my own education, for Cattleyas, is a drench of CALiMAGic once a month enough?

Is there any benefit to a dusting of maybe a teaspoon of powdered oyster shell instead of the other solution.

[Leafmite]

Some Cattleyas have ancestors that get a constant source of Calcium due to where they grow and seem to need more Calcium than other Cattleyas...and this should be a constant source. I have tap water with a good amount of Calcium so I have been using this for the past few years and that has taken care of most of the Calcium issues.

If your plants are still outside, powdered milk/milk added to the watering can each time you water provides an easily absorbed source of Calcium. If your plants are indoors, Crushed oyster shell is a good for a slower release of Calcium. If you still have that Cali-magic, I would add a little every time you water and also used the crushed oyster shell. You seem to have one of those Cattleyas with ancestors that need more Calcium. Might as well get a couple of Angraecums to go with it!