Scalding Under Artificial Lights? or Disease? - Orchid Board

flowerchild · #1 01-23-2009, 06:50 PM

Hi All,

I am new to this forum and am desperate for some advice from you experts!

I have been growing orchids for quite a while now and about a year ago was forced to move my collection under artificial lights when I moved to an apt with a north exposure. My setup consists of several shelves, each with 2xT12 and 2xT8 full spectrum lights (from Verilux) which are on a timer and run for 12 hrs a day. I have a space humidifer in the room to help with humidity.

I was under the impression that you couldn't burn plants under artificial lights but over the past 6 mths or so many of my plants have developed what looks like scalding on the leaves. (Yellowing splotches which eventually turn to black spots- sometimes ending in loss of leaves.) Sometimes the psuebulbs even have the marks-but they still flower.

At first I panicked, when I saw the black spots-thinking I had a fungus or a virus running rampant through my collection so I started repotting and soaking/spraying with Physan 20. But it made no difference. Now I don't know what to think...

Among those affected include my vandas, dendrobiums, oncindiums, and some of my catts. Almost all of my vandas have flowered despite the splotches and many of my oncinduims with the splotches have also flowered....I've had no success with the catts.

I have attached a few pictures of my setup and the splotches on various affected species. Any help/opinions you have would be greatly appreciated.

Thanks! (Please excuse my terrible spelling!!)

Magnus A · #2 01-23-2009, 08:16 PM

What is the distance between your plants and the bulbs? With T12 and T8 it sounds very unlikely tha you have "light" burns.
I would put my money on fungus! How about air movement? Do you have any fans?
/Magnus

Ross · #3 01-23-2009, 08:30 PM

I agree with Magnus. I can't imagine any scenario where T12 or T8 would ever cause that kind of damage. I think it may be a case where something you did (or didn't do) caused the outbreak, in sequence with the lighting?

flowerchild · #4 01-23-2009, 08:57 PM

Thanks for the quick reponse.

I have one osscilating fan that is on the same timer as the lights- so it runs about 12 hrs a day as well...

And the distance from the between the lights and the plants ranges from 5-8 inches (depending on the height of the plants). The vandas were getting closer than this as they got taller- but I removed them from the shelf as they got too tall and the splotches appeared.

I suspected fungus, but the Physan didn't seem to be helping... any further suggestions to eradicate this problem?

Thanks again.

nhman · #5 01-23-2009, 09:21 PM

The other possibility that should be considered given one of your photos, is viral infection.

One can test for virus using a "home" testing kit made by Agdia to prove or disprove this. I test every plant before "releasing" it into my collection and am surprised at the plants that test positive.

I would agree with the above comments that using the light setup that you are using, it would seem very very difficult to cause any leaf "sun" burns. A T-5 bulb, THAT would be another story!

Good luck.

MuscleGirl'sHobby · #6 01-23-2009, 10:29 PM

I'm no expert, but I'd have to agree with nhman. I've seen pictures of virused plants that look remarkably similar to your own.

But, I'm a big scaredy cat who panics "oh no! virus" every time something starts to go awry in my collection. Perhaps I should just test them all!

nhman - That's not a bad idea, to test every new plant. Doesn't it get a bit expensive though? I priced tests and they were upwards of $25-30 a piece! Do you know of a place to get reliable tests for less?

flowerchild · #7 01-24-2009, 12:01 AM

Virus... that's unsettling. I looked into the Agdia ImmunoStrip and it seems to only test for 2 viruses: Cymbidium mosaic virus and Odontoglossum ringspot virus.

I will order the tests right away. If my collection test negative for these two am i in the clear? Or do i need additional tests for other viruses?

As far as bacteria/fungal infections, do i need to repot and soak each orchid roots and all? or will spraying with Physan 20 conquer the problem?

Sorry for all the questions, but apparently this may be more serious than i first thought...

camille1585 · #8 01-24-2009, 08:16 AM

I also agree that some look viral too me, especially the first onc pic and the new den growth. Those light colored spots look like typical virus symptom. Of course, the problem is that viruses are extremely hard to diagnose visually, even for experienced virologists.

For your sake, I hope you have something bacterial going on. In that case, spraying with Physan 20 or other things will not remove the spots that are already there. The spots just won't spread anymore.

Testing with the strips will eliminate 2 possibilities, which are the most common in orchids, but orchids can be infected by a wide variety of viruses

flowerchild · #9 01-25-2009, 05:24 PM

Hi All,

Just as an update, while i wait to be able to ba able to test for the viruses i've been operating on the pretense that i have a fungal/bacterial problem.

I have physan'ed the crap out of my collection and tipped a few pots to see what is going on below ground.

I was somewhat relieved to see that the affected vandas and catts had experienced significant root damage-there's something i never thought i'd say...

Their potting medium had not decayed, but must not have been drying out as fast under the artificial light.

My oncindiums, and brassias and dendrobiums all looked good- below ground anyways...

i did some (lots actually) of reading on the web and it seems like there are a few fungal and bacterial infections that start out with yellow blotches that turn into black spots, similar to the appearance of a virus. So for now i'm keeping my fingers crossed that i have one of those; and that the physan will kill it!

Thanks again for all the advice. Your input is much appreciated.

nhman · #10 01-25-2009, 06:35 PM

The two viruses that the Immuno strips test for are - by far- the most common in cultivated orchids. They also seem to cause the most damage to the plants. Therefore, if they don't test positive to either of those two, you should be "Free" from the bad viruses at least.
FYI to those tobacco smokers out there too: remember to wash your hands after smoking so that you don't potentially infect you plants with a virus.
As to cost - well, when ordered in bulk (that's 25 at a time) the tests cost about $5 each and are good in the fridge for over 1 year. Compared to the price of some plants, the cost of a whole collection, the cost to care for them, etc. it seems a reasonable step to go through.
Good luck and let us know what you determine is the cause of your plants failing health!