Are copper based fungicides harmful to Dendrobium and thin leafed orchids?

[Lupus]

Hello,

a couple of weeks ago I transitioned my cool growing collection from unter lights (because of the summer heat) to my small greenhouse. Last couple of days I have had bacterial and/or fungal problems on some orchids there. I sprayed with Physan20 and after a couple of days also with a systemic fungicide, but some orchids are still affected. So I was considering using a copper based fungicide/bactericide.

So whats the story with the copper and dendrobiums or thin leafed orchids? Here and there you may reed that it is harmful, but I could not find any viable information in the internet.

The only personal experience I have, is with Dendrobium vexillarius, which I sprayed very heavily with a copper fungicide in spring by accident. It was completely drenched and after I noticed, I got very worried. But nothing happened. It bloomed all the time and grew very well and still is.

So is this copper-dendrobium-thing a myth? Or are just some species/sections of dendrobium affected and if so, which? What about Lepanthes or Dracula?

Cheers

[rbarata]

Welcome Lupus

Yes, it is. Read this and this.

[Ray]

I suspect that "dendrobiums and thin-leaved orchids", an expression I have used myself, is simply too broad. There are likely some plants that don't react while others do.

The simple fact is that copper is phytotoxic if applied in the right concentration, and that concentration likely varies drastically from plant to plant.

There is bound to be a gradient from no effect to curative to toxic. Where the breaks are is anyone's guess.

[SouthPark]

Originally Posted by Lupus

also with a systemic fungicide

What systematic fungicide did you use? A collection of various sorts could be handy. Even some non-systematic ones.

In my kit, I just keep thiomyl, yates anti-rot phosacid, captan, mancozeb.

[Lupus]

Thanks for the input. I sprayed yesterday anyway, we'll see what happens, but so far nothing. One day is to short to say anything though, I guess.

Originally Posted by SouthPark

What systematic fungicide did you use?

I don't think you'll know it. Its Compo Duaxo. Had quite good results whith it in the past. The active substance is Difenconazol 16,7 g/l. Thats what it's called in german anyway, I have no clou of the english name.

I need to take the last plants inside now, there is some heavy frost coming ...

[Lupus]

Just in case anyone is interested: after about a month all orchids are well after I sprayed with a copper fungicide. Neither any Dendrobium nor Lepanthes or Dracula are negatively affected. The only plant that seems to be, is not an orchid but a Cyperus papyrus. Though I can not for sure say that it was the copper fungicide, it seems to be the case.

[DirtyCoconuts]

glad they are doing okay

[SteveM]

I have sprayed Coelogyne several times with no negative effects. I do not use very often.