Cattleya seedlings black patches

[My Green Pets]

These were totally fine when they were growing in sphagnum. I moved them to better gro bark mix in November and have been battling blackening leaves ever since. I started spraying fungicide recently and doused them all in Physan 20 today.

What am I doing wrong? Someone's going to say something about calcium, I just know it









Meanwhile, mounted seedlings growing right along, no issues whatsoever.

[Whimgrinder]

I've read several reviews that suggest the mix encourages some pathogenic fungi growth. But how true that is I cannot say.

[wintergirl]

I use Better Grow for all my catts and I don't have black spots. Of coarse I have egg shells in all my pots

[silken]

It probably is a fungal or bacterial growth but having enough calcium helps them not to succumb to such things. I think more nutrients might be available when in moss than in bark and so maybe had enough calcium then but not now. Didn't want to disappoint you on your expectation that calcium would get mentioned!

[NYCorchidman]

That possible black rot (pythium) is best to be cut away as soon as you see them as they tend to move quite fast killing the plant.

The other picture looks like the beginning of anthrocnoce. Also must be cut away.

Do not splash water onto other plants.
Try isolate the affected ones until they no longer show symptoms.

These are not calcium deficiency, which usually shows up on the newly developing leaf near the tip or on the upper edge.

Physan 20 won't do anything to these diseases.

[My Green Pets]

Ok, so I am putting a plan into action:

1. Spectricide Immunox Multi-Use Fungicide will be used to deter growth of pathogenic fungi.
2. Well water with "Very High" levels of Cal (100 ppm) and Mag (45 ppm) will be used on the plants. I will mix this 50/50 with tap water.
3. Crossing all my bits! (phrase learned from an English friend )

[Becky15349]

I agree - this is systemic fungus. Such a bummer. I would say cut off the affected areas and hope for the best. Maybe this growing media isn't ideal, I've never used it myself - I just stick with large chunk douglas fir bark.

[WhiteRabbit]

I've used better gro bark (not the mix), and haven't had any issues with it

[Orchid Whisperer]

I use the Better Gro orchid bark (fairly certain it's Douglas for bark) with good results. Cut away black when it appears, make sure plants get calcium when actively growing, hopefully your problems will diminish.

[My Green Pets]

I just called the water company and they said our tap has between 50 and 100 parts per million of calcium. Isn't that enough? Surely not so low as to cause deficiency symptoms. (?)

I am starting to feel like the moisture and cool temperatures are to blame. Although like I mentioned before, the mounted plants have no issues. Of course they dry out faster, even in cool temps.