contagious rot in Cattleya new growth

[Ray]

I am going to be a "nay-sayer" again on the calcium deficiency.

As it grows, all plant tissue needs a steady supply of calcium. Unlike most other nutrients, calcium is not well transported within the plant - once absorbed and used, it is "locked down" - so old tissues cannot supply it to newly-growing ones.

That being the case, the classic symptom of calcium deficiency is the blackening (death) of new growths as they emerge from the plant. In these photos, it is apparently that they grew fine and then contracted an issue. This could only be a calcium deficiency if it had been adequately supplied, and then stopped altogether when the growths were partially mature.

[SundayGardener]

I also have this problem with my cattleyas. Or perhaps two problems. One is that the new growths have new leaves coming out that are black. The other is overall blackening of leaves.

There should be plenty of calcium in my water, since I switched to tap water for the catts and we have hard water with a lot of lime. I also added oyster shell as a top dressing to the pots. In two cases, adding additional calcium did resolve the issue, and the leaves went back to a normal color.

I really doubt that I am overwatering in the sense of watering too frequently, since typically I am advised that I am underwatering. However, I may be overwatering in the sense of providing too much water at the times when I do water. Depending on a given plant's schedule, like the original poster, I will water once a week, and I might let the plant soak. I tend not to do this in the winter because it doesn't work well, especially not for catts, which I don't let sit in water for longer than 10 minutes. It is convenient for me though, because it takes longer to repeatedly drench a plant one by one. With soaking, I can have multiple plants in their respective private tubs, then drain them and it's usually more efficient (for me, maybe not great for the plants). When I don't soak, I drench, which is what is usually recommended--to imitate rainfall. But I find it hard to water from the top without spashing and getting leaves wet. In any case, I have noticed that I have symptoms of plants getting too much water at one time--a variation of overwatering?

Then there is what looks like brown spot, but it doesn't respond to the recommended treatments. So it is frustrating, for sure. I cleared and wiped down an entire shelf with Physan to disinfect the growing area, but it's about guaranteed that any plant that I put on that shelf will develop spots, typically on the youngest growths.

Not to derail, just saying that I have tried bumping calcium with some success, have switched water and changed up how I water, and continue to seek answers. Also, I have several catts that receive the same care as the others and are located on the "danger shelf" and have absolutely no problems whatsoever.

[Orchid Whisperer]

Originally Posted by Ray

I am going to be a "nay-sayer" again on the calcium deficiency.

As it grows, all plant tissue needs a steady supply of calcium. Unlike most other nutrients, calcium is not well transported within the plant - once absorbed and used, it is "locked down" - so old tissues cannot supply it to newly-growing ones.

That being the case, the classic symptom of calcium deficiency is the blackening (death) of new growths as they emerge from the plant. In these photos, it is apparently that they grew fine and then contracted an issue. This could only be a calcium deficiency if it had been adequately supplied, and then stopped altogether when the growths were partially mature.

Wrong again.

This evening I will post a presentation given this past weekend at the Northeast Georgia Orchid Society. Not my presentation, but one developed by one of our members (professional horticulturalist, master's degree). A part of his presentation focused on Ca deficiency, the symptoms look like the OPs problem. Could easily be caused by very high puriity water, lacking Ca. Easily corrected.

Before we go there . . . not caused by too much K either.

[Ray]

Originally Posted by Orchid Whisperer

Wrong again.

Now THAT made me laugh out loud!