Sunburn?..Fungus?..Disease?..HELP NEEDED!

[mia1aab]

All:

Several of my Cattleya orchids are experiencing what I would characterize as a serious attack and I have no idea what is causing it. I've separated each plant with pictures so it's easy to follow. A little background on my growing area -- The plants are set on top of a glass table and are spaced about six inches apart. They receive the east morning sun until about 11 am and then remain shaded the rest of the day. I was watering once a week, but have since started watering twice a week because the days are hot and humid this time of year in South Florida. I fertilize once a week at full strength and started to spray bi-weekly with Physan 20 to prevent the outbreak of disease since the rainy season is here as well.

Pic 1&2:
The psuedobulb on this catt is changing colors from green to orange and then back to green and now it's orange again. No idea what's happening here.

Pic 3&4:
This catt has lots of new growth and is preparing to flower soon. I moved it to an area with a little more direct sunlight and when I got home two leaves were black and then turned brown. The following day it started spreading to the other leaves. I thought it was sunburn but now I'm questioning that....

Pic 5:
I noticed a brown spot on the leaf of this catt two days ago and now it's spreading over the whole leaf....

Pic 6&7:
The leaf on this catt started to turn a light color that spread very slowly. Now it spread to another leaf. Again, no idea what is happening.

Pic 8:
This last one is Beallara Marfitch 'Howard's Dream'. I moved the plant inside when the flowers opened and then noticed the change in leaf color from green to light yellow and then eventually brown. I moved it back outside immediately to a slightly shaded area but the leaves are still turning yellow. It's spreading to all the other leaves now also.

Any help is appreciated in identifying what is going on here!!

Thanks...mia1aab

[mehitabel]

Can't be sure about the others, but Pic 3 & 4 and 6 & 7 look like sunburn to me. Sunburn can take different forms, sometimes that black/brown color, sometimes white.

The fact that the injury is on the broad part of the leaf where the sun would hit directly also sounds like sunburn. A "little more" sun this time of year can be way too much, depending.

#5 looks like it could be some kind of rot. Does the brown go all thru the leaf? If so, feel the leaf in the brown area is it soft, rottenish? I would cut out the brown places, using a sterile blade and cutting into fresh, unblemished tissue. Then dust the edges with cinnamon. That may stop the rot. This kind of rot (if it's that) can spread by water splashing, so I would move this plant away from the others.

#1 & 2-- can't say. But feel the area, see if it's soft or hard, for starters. Also peel off the sarong, see what's underneath.

The last picture-- can't tell, but it could be sunburn as well.

[mia1aab]

Does sunburn continue to spread throughout the plant even when it's moved to the shade? The reason why I ask is because the brown marks are spreading throughout the other leaves.

[PhalNewbie89]

I could be wrong but I don't believe sunburns move. It is kind of like a huma sunburn. It is just a part of the plant that got a bit more sun then necessary.

[mia1aab]

Well all the pictures with black/brown leaves has spread throughout the plant over the past 2-3 days so I'm questioning whether it's sunburn or not. What do you think it could be then?

[11Orchid126]

In pictures one and two, if you're talking about the dry papery rapping at the base of the bulb, this is a "tunic" of sorts that covers the bulb until it matures, and then no longer needed, it dries up. This material can be safely peeled off.

Mehitabel is correct, this looks like sunburn. Have you recently used a horticultural oil or neem oil on them? Sundburned leaves, other than being unsightly, require no special care.

The two dark spots that are spreading may suggest something else. They look bruised. Are the spots spreading? You might want to take a marker and go around the edges, and then you will know for sure.

[mehitabel]

No diagnosis is ever certain, even if you're looking right at the plant. That's why doctors do tests-- to exclude possible causes.

The brown spots are either rot or they are sunburn. If they are rot, it is a fast-moving, bacterial rot, and you had better move fast to get the plant isolated, and the rotten pieces off it before it spreads. This kind of rot can be spread by water splashing. It's a serious problem and requires fast action to remedy.

Can sunburn "spread"? Yes, sunburn ius dead tissue caused by intense heat. Some of the tissue might die a little later. Really bad sunburn can turn the leaf to mush.

You need to decide what you think it is and take action.

[kmarch]

Pics 1 & 2 show the normal dieing off of the protective bracts. Bracts protect the growing and developing pseudobulb and leaves. After they are mature the bracts are no longer needed so they die off and dry up. This is normal.

Pics 3, 4, & 5 - If these brown spots are spreading quickly, as in they are getting noticeably larger by the day, immediately cut the whole leaf off. These fast moving brown spots are bacterial infections and if left unchecked they can kill an entire plant in a week or 2. They are also usually soft and frequently mushy.

Pics 6, 7, & 8 are sunburn. Give your cattleya a little more shade or perhaps dappled sunlight.

[berniep]

G'Day mia1aab

Firstly welcome to the forum, I'm with Kevin on 1 & 2, peel the protective bracts off as they die off it will make a nicer look and also less places for nasties to hide.

How do you water the plants? With spray or from the base of the plant? If spraying in the sun its the equivalent of having a steaming hot shower and will burn the leaves. Also if you have any oil on the leaves in sun it will burn them.

Just my thoughts let us know how you go.

Cheers
Bernie

[orchids4me]

Hi and welcome to the forum.
You mentioned also you fertilize full strength every week I'm not sure if that's a contributing factor except for mineral salts build up are you flushing your pots? I fertilize mine once a month at full strength and the next 3 weeks I flush when watering .... Are they in clay pots or plastic? I would if you want to fertilize weekly do it weakly weekly... 1/4 strength. Look for white build up around bottom edge of your pots scrub that off and flush the pots. You might want to check your roots as well make sure they are healthy looking.
Hope this helps some along with the others that have posted
Emmaye

[orchids4me]

Oh one more thing I thought of... Do you have your catts in a coarse potting media? They need ther roots to breath and dry a bit between watering if the mix is to fine it will hold to much moisture and cause root rot use clay balls or packing peanuts in the middle of the root ball on them so they can breath and dry enough... I have mine this wayand they are doing wonderfully.
Emmaye