Spot treat with Physan on Den aberrans?

[nzadro]

I got this small Den aberrans from a friend. It has some black spots on the leaves, we were unsure if sun burn or other fungal/bacterial spotting. As a precaution I dusted some freshly ground cinnamon on the leaves. Would spot treating Physan 20 directly with a small brush on the spots help? I only got this yesterday, so unsure if it is actively spreading or not. Is isolation also a good idea? Image attached, note, the spots look greyish due the cinnamon, but I assure you they are black. Thanks.

[SouthPark]

nz ------ I know that growers in the past (and probably even now) use physan - a disinfectant.

If you do choose to use it, the physan 20 site reckons 2 teaspoons per gallon, which comes out to around 2.6 mL physan 20 liquid per 1 litre of fresh water.

I don't use physan 20 for orchids though, even though I do have physan 20 - but never used it heheh. Actually, the bottle says SA-20, but pretty sure it's the same thing.

For your case, if you have non-systematic fungicide like mancozeb, then could try that. Or if you need to use a systematic - could consider monterey garden phos, or copper spray (for orchids and plants), or cleary's 3336 - thiomyl.

At the moment, you probably don't need to apply anything at all. If not provided already, then provide some gentle air-movement to cut down on or eliminate chances of fungal/bacterial activity on leaves.

And if you notice the lighting levels have been a bit high, then just put the orchid in a spot with slightly less maximum light intensity.

Monitor the orchid's condition. If the spots don't spread, and the just dry up (or remain dry), then you will probably not need to apply any disinfectant or treatments.

How long roughly had this orchid been growing - in the particular area that it is currently growing?

Also ---- nz -- at least some of my orchids growing semi-outdoors gets spots like that too on some leaves. No issue with those particular orchids. It's just a part of growing semi-doors (for my orchids that is). So black spots aren't always a problem! Orchids in the wild do get it too - eg. if something happens to bite on it, or the sun gets a little too intense - or something. All part of living outdoor or semi-outdoor.

[nzadro]

THANKS SP!!

I am unsure when my friend got the orchid, it orginally came from J&L. I can ask, but sorry to not have an answer. He has mentioned some struggles with bacterial spots in the past - why I thougt perhaps it could be the culprit. I don't have any other fungicide other than physan as of right now... btw I have been told that den leaves are particularly sensitive to copper sprays, I am further looking into this to learn more.

I took care to water the net basket carefully and not get any droplets onto the leaves. Ill grind some more cinnamon tonight. I took some images last night to reference any new spotting. The orchid has two new bright green active growths, so it must be happy otherwise. Ill keep an eye, but also the Physan ready 🙃

[SouthPark]

Most welcome NZ.

If the spots just stay like that - and no spreading when gentle air movement is provided in the growing area, and leaves kept dry, then everything should be fine and under control.

I have heard that some growers had issues with copper spray on dendrobium. I don't know what concentrations they used. I did recenty test copper sulphate spray on a Den. moschatum ----- sprayed quite a fair bit on - just as a test, and no problems resulted at all ------ at this link. The copper sulphate solution seen in the pics was quite nice and blue.

I also have Den. discolor to try it on too later.

I only tested as a ..... test. I think that much more testing should be done lots of times on various dendrobium - with recorded copper concentrations, and growing conditions etc ....... in order to really find out how the dendrobiums got impacted negatively by copper ------ when those growers used it that is.

So the moment, unless there's no other option - could certainly skip using copper on dendrobiums. I will try it on my Den. discolor very soon though!

[nzadro]

Okay, I will keep an eye. Hopefully it doesnt spread...do I keep it isolated? It is in my sunniest part of my windowsill next to my den Emma White.

Let me kbow how the further tests go! I am so curious. Just a test or were you eradicating something? Did it help?

[SouthPark]

Originally Posted by nzadro

Okay, I will keep an eye. Hopefully it doesnt spread...do I keep it isolated? It is in my sunniest part of my windowsill next to my den Emma White.

Let me know how the further tests go! I am so curious. Just a test or were you eradicating something? Did it help?

NZ ------ from the look of this case here, it should be ok to keep the orchid there. Just monitor the dark spots. If they don't grow in size or get many more dark spots, and looks dry, and the other leaves remain unaffected --- then it should be ok.

Just keep an eye on the growing area - just in case. Watch for too much light coming in, or too warm/hot window sill, or too warm leaves if sun comes in strongly. Also - gentle air-movement in the growing area does help to reduce or eliminate fungal/bacterial activity on leaves/stem.

And every once in a while, provide weak fertiliser, and later provide weak mag-cal. I usually add weak fertiliser on the first day of each month, then weak mag-cal at the middle of each month. These applications can help nutrient or element deficiency ----- and some kinds of deficiency are known to lead to patches etc - giving the impression of pathogen attack (while not a pathogen attack).

NZ ---- the copper spray test wasn't for testing copper on my dendrobium only. It was a very healthy plant (and still is - after that test).

Sure will - I will likely do a copper spray test on Den. discolor this weekend.

[nzadro]

Well, SP, sadly the bacterial issue seemed active since new spots appeared. Despite cinnamon, no wet leaves, air flow and trickles of sun. I sprayed with Physan 20 yesterday. Ratio used was 1 tsp to a gallon & portion in a bottle. I did my best to spray everything! How often is such a treatment repeatedly? Weekly?

Some of the black spots have shriveled as if dried out. Hopefully? Ahhh. Part of me wishes I bought a different plant.

[SouthPark]

Originally Posted by nzadro

Some of the black spots have shriveled as if dried out. Hopefully? Ahhh. Part of me wishes I bought a different plant.

nz ------ black spots shrivelled and dried out is considered good news.

Maintain dry leaves. The physan is a disinfectant - not systematic ---- so if bacterial or fungal activity is associated with the outside of the plant, then that can/could help to handle those organisms.

But for attacks going on both outside and inside the plant, systematic treatments should be considered ---- eg. monterery garden phos, copper spray, thiomyl and other treatments ----- if the pathogen (assuming there is one or some) is not identified ----- then it may take time to get a treatment (assuming there is one) to take care of the attacker.

It can be beneficial to encounter situations like this, so that you can then grab the knowledge that comes out of it. And eventually you come up with your own system - and will have minimal or even no issues with growing this kind of orchid.

NZ ---- I've never used physan before. But if you do, just use it on leaves and stem only. Not on roots. And maybe just use one application and monitor.

[estación seca]

What are your growing conditions? Temperatures, humidity, day and night? Light? How are you watering it?

[nzadro]

Originally Posted by SouthPark

nz ------ black spots shrivelled and dried out is considered good news.

Maintain dry leaves. The physan is a disinfectant - not systematic ---- so if bacterial or fungal activity is associated with the outside of the plant, then that can/could help to handle those organisms.

But for attacks going on both outside and inside the plant, systematic treatments should be considered ---- eg. monterery garden phos, copper spray, thiomyl and other treatments ----- if the pathogen (assuming there is one or some) is not identified ----- then it may take time to get a treatment (assuming there is one) to take care of the attacker.

It can be beneficial to encounter situations like this, so that you can then grab the knowledge that comes out of it. And eventually you come up with your own system - and will have minimal or even no issues with growing this kind of orchid.

NZ ---- I've never used physan before. But if you do, just use it on leaves and stem only. Not on roots. And maybe just use one application and monitor.

That is good to hear, I will keep an eye out. So far nothing augmented as before.

You are right that these are all learning experiences. I only sprayed the leaves, the roots look fine and the two new bulbs are growing well. Wish me luck!

Originally Posted by estación seca

What are your growing conditions? Temperatures, humidity, day and night? Light? How are you watering it?

I grow the plant in a bright southeastern window with either an open window or a fan running for air circulation. Temperatures are around 75 inside, outside temps are high 80s lately, night times a couple degrees cooler by the window. I water when the medium is dry (bark with a tad of spagh), which lately is every morning due to the bright sun. Dries out by night time. I have the orchid sitting on a pebble tray for some extra humidity.