Black pseudobulbs
 

I have had blackening pseudobulbs that eventually blackened up the new leaf. I have cut that off and treated with sulfur powder. I read somewhere in the forum of two other things that would work systemically. I can’t locate that post but one was phos. I purchased that and would like to use it as a drench on all of my orchids but don’t have any idea of how to mix it. The instructions are all for citrus fruit, but and veggie application. Can anyone tell me how to mix it for watering orchids?

We need more information. Pseudobulbs turning black is not usually caused by infection, so chemicals likely won't help.

What is the plant?
How long have you had it?
Where are you growing it? Inside? Outside?
How much light is it getting? Sun or electric?
In what is it potted?
What are the temperatures day/night?
How and how often are you watering it?
What is the humidity?

And photos too. Really important, an image speaks for a thousand words.:)

It’s on brassavola, bc, blc.
Several years
Inside winter, outside summer
Electric 8”-12” away, 16 hours
Partial shade in summer
Shredded bark, lava rock and charcoal
Inside 65+ day, 55 night
Summer ! Uncontrollable. 90°+ today, 70’s tonight. In 2 days high 70’s to 45° night for a few days. Michigan temps are up and down all year.
About 1 time per week winter
As needed in summer taking rain into consideration.
Humidity 45-65% in very cold weather. As it warms up humidity is higher. I can only hose the floor to control humidity.

I grow in winter with lights and a south facing angled skylight type window.

Summer in a summer house, partially shaded by time of day. No full sun. It’s a screened in area because of rabbits, squirrels, chipmunks, possums and raccoons!

The orchids have only been out for a few days because of a late freeze of 25° that lasted 5 hours. There is still shade cloth on the summer house.

The orchids only come into the house while in bloom.

I’ve been unable to add the attachments so I’m sending this before I lose it. I’ll send attachments as soon as I can.

Thank you.

Sunburn commonly causes blackening pseudobulbs in Cattleya alliance plants. With the recent move outdoors, I would suspect that.

Photos
 

Photos 1-3 orchid 1
The rest are orchid 2
Summer House

This has been ongoing for quite some time. The plants have only been outside for a few days under shade cloth in partial sun. This moves from bulb to bulb and I’ve thrown out several plants because they got so bad. It starts at the very base and works it’s way up. I’m positive it’s not a light problem

I’d really like to know how to mix the pho’s for a drench

Dulcinea - do you mean phosacid? I use this item here, maybe yours is similar, if it's phosacid that is.

Click Here

5 millilitre of my phosacid solution per 1 litre of water is ok ----- for the concentration that is.

The items generally have the recommended concentrations.

The plant in the photo looks severely dehydrated. Either you haven't been watering enough for a long time, or the roots have been bad for a long time. That will cause blackening of newish growths.

Totally agree with E.S. about the dehydration. The pseudobulbs are really shrivelling up to levels that look concerning.

Dulcinia ..... just go ahead to unpot, and check the roots to see if they're ok. Sometimes, if the roots aren't dying due to being overly wet ----- they can also die if the bark or media develops a layer of fungus ----- and the fungus makes the bark repel water, so that whenever you water the bark, the water goes right through the pot - leaving hardly any water to go into the bark media, and the orchid can die a slow death due to dehydration that way.