Oncidium diseased leaves
 

Hi, I bought a greenhouse last summer and got a bit carried away with the humidity and misting systems, as a result all my Oncidiums now have a fungus affliction.

I know not to hand water their leaves but didn't extend that to automated irrigation and have learnt a lesson.

Would someone be familiar with specifics on what I've managed to infect them with, and what the best treatment is, I've tried cutting off the leafs with cinnamon applied but wondering if a copper anti-fungal, systemic or mancozeb should be my next step as it doesn't seem to have stopped and don't want to lose the plants.

I have also since stopped watering them besides by hand and relocated them outside to get fresh air but Winter's here in Sth Aus and nights are around 7c/45f so may exacerbate the issue.

Thanks

Just give them some gentle air movement, which is what you're providing now already I think.

I have read that thin leaved orchids can get issues with copper. Maybe just go for gentle air-movement, and yates anti-rot (from bunnings or any place that sells it).

Or - certainly, you could try mancozeb too ... spray leaves, all over, and stem. But mancozeb is not systematic. But could work too.

Ok thanks, I've grabbed some Yates Anti Rot and will try that. I'm concerned wetting the foliage and will try the drenching method and monitor.
Cheers for the help and the product reference, if you're aware I see mentions of kelpmax and rubbing alcohol alot, would you know what the local equivalents of these would be - Seasol and Metho?

Keeping them warm and the leaves dry are the big issues. If things get too cool, I will also get spotting like this. No treatment will fix the existing blemishes, so the key to seeing if the change you made is working is to look at the new growth.

Thanks for the reply, I'm ok with the blemishes as long as it doesn't spread and kill my dozen Oncidiums.

I believe California may have a similar climate to me. Generally speaking what would you consider too cold for an Oncidium intergenera that may also cause this, I'm leaving an Onc Golden Anniversary outside currently at night to test the tolerance/limit I think it will be around 40f tonight.

Hi there fred. I have heard growers in Australia recommend Seasol before. It will probably not be the same as kelp max in terms of exact features, but should be just fine.

Now that I think of it ........... I do remember something -- it will definitely accumulate in media (in pot etc) too much if applied relatively strong and too much. So growers often just tone it down a bit --- like quartering (one-quarter) their written recommended levels. And maybe just apply weakly every 2 weeks or even every 3 weeks. All my orchids just get weak fertiliser into the media just once a month ----- around the first day of each month --- easy to remember heheh.

Not sure about the usage of isopropyl alcohol (aka rubbing alcohol). I haven't used that for orchids before. I know that alcohol can do that 'cooling' effect on plants (leaves etc) and can create issues for some plants ----- maybe chilling them too much or something. So just might have to read up on that if using alcohol. Isopropyl can be purchased from bunnings ..... I have seen it there. Otherwise, ebay certainly sells isopropyl ..... I bought some from ebay eg. 500 ml bottles ...... for spraying on door handles, elevator buttons at work heheh.

You probably have a bacterial or fungal infection epidemic going on in that enclosed space. You may safely spray the entire greenhouse - plants, benches, floor, structure - with something as mundane as diluted liquid bleach. Here, the standard bleach is about 5% sodium hypochlorite and an ounce per gallon works fine.

If you can get Physan there, or a swimming pool disinfectant containing quaternary ammonium salts, they’re good too.

Being topical treatments, none of those will cure infected plants, but it will reduce the spread.

Copper compounds can systemically kill both fungi and bacteria, but it’s supposed to be toxic to dendrobiums, so be wary.