Black rot in collection

[Orchid Whisperer]

I had this on one plant recently and so far it seems like I have stopped it, including the affected plant, which is isolated from the others. I will need to inspect all plants daily to be sure - probably will need to do for a month or more.

I do use calcium (about 5cc gypsum dissolved per 4 liters water, or 1 teaspoon/gallon) frequently throughout the year, maybe this has helped limit the spread?

[estación seca]

Most of the things I read dealt with commercial crops grown in the ground, which would have ample calcium. I didn't see calcium addressed. I have read adequate calcium is important in preventing orchid diseases.

A common recommendation was to incorporate large amounts of organic matter into growing fields with clay soils, to promote growth of beneficial organisms and to improve drainage of heavy soils. I bought some Inocucor from Ray to see whether it might prevent such problems in my orchids.

[Silje]

Just an update on my progress.

Because of limited chemicals available I opted for removing all my plants from their growth medium and apply the 3% hydrogen peroxide solution. I also used some alcohol on some of the plants and I covered the cut edges with cinnamon. The very next day I have more blackening on several of the plants. Growths that had been fine the previous day when I cleaned them up. Teeth-grindingly frustrating and...heartbreaking too.

At my wit's end I went crazy with the cinnamon, and sprinkled it on all rhizomes, into all crowns...everywhere. Since then there has been no more blackening leaves and no visible rotting of roots or rhizomes. *Sigh of relief*

I don't dare to pronounce the Black Plague beaten just yet, but at least I've slowed it's progress considerably. I've been knocking my head into the wall wondering why I didn't sprinkle cinnamon everywhere earlier instead of just a bit on the cut tips.

Now the eyes on several of the cattleyas ar swelling and I have roots that start to poke out through the cinnamon! So I have another question. I thought cinnamon and roots was a no-go because it dries them out? So, should I rinse the cinnamon off now, since I'm in dire need of healthy new roots? Or will new roots actually shoot through the cinnamon and remain healthy?

[estación seca]

I don't know the answer. The black rot organism lives only in water and in wet tissue. It spores can survive drying out, but not the active pathogens.

I would take the most advanced-growth plant, wash off the cinnamon at the start of a warm period, and let it dry completely. Then I would put it inside something with high humidity but no water. If it's OK in a day or so, I would follow with a few more plants, then a few more.

The plants should continue to grow new roots. When they are as long as you think they should be, repot the plants. Take care they dry out well between waterings, though of course not the plants that can't tolerate complete drying.

The fact the people report these epidemics come and go suggests to me a balance is re-established with other microorganisms that prevent the water molds from staying dominant.

[AussieVanda]

I prefer to use phosacid.

[Orchid Whisperer]

Originally Posted by Silje

So I have another question. I thought cinnamon and roots was a no-go because it dries them out? So, should I rinse the cinnamon off now, since I'm in dire need of healthy new roots? Or will new roots actually shoot through the cinnamon and remain healthy?

Using some colloquial American English, there is an old saying "If it ain't broke, don't fix it.". Keep doing what you are doing as long as it is working.

I assume you are not watering plants until the rot stops spreading. When you are fairly sure you have it stopped, would it be possible to use either a blower or a vacuum to remove most of the cinnamon without wetting the plant?

When you do start watering again, probably best to do so on a windy day, hose off the cinnamon and let the plants dry quickly.

[Leafmite]

With the new growths, just be certain to add calcium to your fertilizing mix. You will need something that delivers immediate calcium but for long-term, you can add eggshells (they take a while to decay enough to start providing calcium to plants).

[azredsand]

AussieVanda--what is phosacid and how do you use it?

[AussieVanda]

Originally Posted by azredsand

AussieVanda--what is phosacid and how do you use it?

I use it as a foliar spray and find it extremely effective. It is not an actual acid!

This may assist, Phosphorous Acid Fungicides | Sub-Tropical Fruit Club of Qld Inc.

as may this http://www.colostate.edu/Depts/SLVRC...rSRMAC2011.pdf

[Silje]

Originally Posted by AussieVanda

I use it as a foliar spray and find it extremely effective. It is not an actual acid!

This may assist, Phosphorous Acid Fungicides | Sub-Tropical Fruit Club of Qld Inc.

as may this http://www.colostate.edu/Depts/SLVRC...rSRMAC2011.pdf

This sounds so interesting and I'd love to try it, but I can't find any suppliers of phosphorous acid fungicides in Namibia. :/

This is another challenge that I have regarding anything orchid related. My access to both plants and chemicals, as well as growth mediums is very limited. Leca, coco husks, sphagnum...? Forget it. Unless I bring it with in my backpack when I've been abroad, it's not available to me. I'm left with bark (readily available at nurseries) and mounts collected in the bush as my only options.