curious spots on a dendrobium - Orchid Board

djuna · #1 07-08-2013, 04:32 PM

windswept but otherwise sunnyblue summer greetings from finland...

i've been looking up on orchid sites trying to identify what may be ailing this noid dendrobium (phalaenanthe).

the spots on the leaves were present when i got these back in april. since bringing them out in the summer i have misted the leaves in the mornings. i cannot say for sure but it seems like the spots have grown a little in size but not in number.

based on what i could find out, possible causes are:
- brown rot
- guignardia/phyllosticta Leaf Spot
- fusarium wilt (the yellowed leaves)

as the spots are scattered throughout the leaves, might i need to lop off the whole leaf?

and will the plant survive if all leaves have to go?

diagnosis and advice from a more experienced grower would be greatly appreciated!

WhiteRabbit · #2 07-08-2013, 10:08 PM

What temperatures is this getting?

djuna · #3 07-09-2013, 09:28 AM

they are outside in full sun under a white sheath, temperatures 25-30C, sometimes a little warmer. i bring them inside in the evening, before the temperature starts to dip below 20C.

WhiteRabbit · #4 07-09-2013, 09:19 PM

Hmm ...

The dying leaf (is it just the one?) could be typical shedding.

I don't know what may be causing the spots, but does look concerning.

Hopefully some others with more knowledge in this area will be chiming in!

djuna · #5 07-11-2013, 03:18 PM

Hi again, Sonya. Thanks for the quick reply. If you recall from another post treating 3 dendrobiums in 1 pot this is one of three groups that i first repotted as three separate groups into one pot but due to one group becoming quite shrivelled i have had to repot them a second time into individual 3-inch pots. this is the same group that was more shrivelled than the others and it also has the most spotting of leaves. a second group has some spotting in the mature pseudobulb as well as the strange colouring of the smaller pseudobulb. i will post some more pictures in a few days' time.

at the moment, i think i shall do a little more research on these spots before i decide to cut the leaves and apply cinammon.

hopefully somebody will comment.

thanks again.

WhiteRabbit · #6 07-11-2013, 11:00 PM

Good luck!

djuna · #7 07-14-2013, 12:09 PM

here are more pictures of the dendrobium phalaenanthe group. except for spots numbered 1 (my guess is edema) and 2 (no guess what it is yet) there does not appear to be cell collapse on these spots. the the surface is fairly uniform with the unaffected surface of the leaves. on more hindsight these spots neither appear to have changed in shape or number since i bought these in april. furthermore i seem to recall that some of the flowers had some dark brown streaks on them, only i was too happy a beginner to take serious notice. i am starting to fear this is a virus.

djuna · #8 08-22-2013, 05:43 PM

Because of the paucity of responses here for this thread, i made inquiries elsewhere when after reading through much literature about orchid pests and diseases online i still could not find a match. Well, i still don't quite know what the spots are but Sue Bottom of St. Augustine Orchid Society was kind enough to put my worries to rest. i obtained permission to reproduce her email here in case it might be of some use to somebody else.

+ + +

Hey Margaux,

I don't think you have anything to worry about with your dendrobiums. That is not virus so you can eliminate that concern. If the leafspots were present when you got the plants and they have not grown in size and number, there is not active disease. They may have been exposed to a bacterial or fungal infection at some point before you got them but it is not active so is nothing to worry about. The spotting on the flowers could simply be mold from high humidity. Re question 1, whether the spot is edema I cannot tell, usually you would have more than 1 spot if it were edema, but your description sounds like edema. Re question 2 I think you're probably right about mechanical damage.

You are doing fine with your orchids... Your biggest concern now will be to keep them healthy and happy during the cooler months. They are really happier outside where they get bright dappled light, lots of air and a day night temperature change. A really bright spot by a window is good but you don't want it too close to the window on cold nights.

Best growing, I feel you may be getting the orchid obsession!

Sue

Leafmite · #9 08-22-2013, 09:34 PM

I am very glad you found an answer. I think the biggest worry is virus...everything else can be treated. Good luck!

NYCorchidman · #10 08-23-2013, 05:40 PM

It is a fungal disease spots. I can't tell you what the responsible organism is, but guignardia/phyllosticta will be very likely as it is common in dendrobiums as well as other orchid genera.

Once an orchid gets this fungus, it is almost impossible to get rid of. You want to cut off the affected area, not the entire leaf, because leaving the spotted area encourages the fungal spore to spread.

Also, for future preventive measure, try not to mist the leaves. Misting is not harmful but it makes it easier for any fungal spore that lands on your plants' leaves to germinate and affect the new host.

As long as you grow your orchids healthy, they (unaffected ones) should be able to fight off this disease on their own. Again, misting aids fungus not orchids, especially so because you already have lots of fungal spores in the air in your home because of these spots on the leaves.

Cutting leaves off do not kill dendrobiums but it does reduce food production for the plant. So I recommend trimming the spotted area not the whole leaf, unless the entire leaf is spotted.
Make sure you use steril cutting tool for each plant.

Oh, I remembered something. If you want to opt not to cut the leaf, then you could use clear nail polish to cover the spots.
This way you seal up the fungal spots and there will be no more spores coming out of those spots.
This is something I read online.

Continue to provide your dendrobiums high light as doing so discourages fungal growth and keeps plants healthier.

Good luck!