Black rot in collection

[Silje]

I'm sorry, I can't take pictures at the moment, but I'm pretty sure that I've diagnosed the problem.

My entire collection is dying of black rot, and at such speed I'm unable to keep up with it.

I don't have a large collection (50 or so plants), and I also don't have anything very valuable, except that some of the plants are personal favorites of mine.

Here is the problem. I live in Namibia and our humidity is around 5% at the moment, so the plants need to be in a room with a humidifier. I live about 500 km away from the nearest town where I can get a humidifier, so I'm stuck with whatever I have available on the farm. That goes for chemicals as well. Since I live on a farm and we're vegetable producers I've been scrimmaging through our chemical room searching for possible fungicide alternatives to the ones I've found on the list of the sticky post on top in this forum, but so far...no luck.

The main problem is that it's freaking impossible to see which plant that is infected until it's too late. Plants have beautiful green tips on the roots, look healthy and well in the morning and in the afternoon the roots have darkened and are drying up. The next morning the rot has reached the pseudobulb. It's incredibly aggressive. This is also why I probably responded a bit slow when the first plant keeled over. I didn't quite understand the severity when the first dendrobium lost a couple of pseudobulbs. Within a couple of days though, it became crystal-clear that I have a huge problem.

Obviously I remove plant immediately when I see sign of infection, but by then it's already too late. I've tried to take them out of the pots, cut the rhizome until it's nice and green (there's no purple ring), put on cinnamon and repotted them in new, sterilized growth medium in a clean pot, but it just seems to speed up the process of rot and until now I haven't had a single successful rescue.

It took my dendrobiums first. Within a week, 8 of them rotted from the bottom. Healthy plants with new growths and good-looking roots. Poff! Dead, gone in a blink of an eye.

They were dispersed in my growing area so it didn't jump from one plant to the neighbor, but the dendrobiums were much more susceptible than the others. Now the cattleyas are starting. The only plants that seem to be immune (at least to now) are the super market phals.

I've reduced the humidity in the my growing room to 40-50% and temperature down to 20-22 Celsius. It's the best I can do. It's 38 degrees outside.

I'm keeping the plants drier and I've spread them out as much as possible to make sure they're not in physical contact with each other. I've disinfected all surfaces with agri disinfectants, I'm using new scalpel blades every time I cut a plant and I work with them outside my growing area. I'm making sure there's no water standing anywhere in the growing area.

I am at a complete loss as to what else I can do that is within my capacity at the moment.

Help..!

[tucker85]

The short term solution is to use a fungicide at regular intervals. Either a contact fungicide or a systemic fungicide. Also increase the space between plants and increase air movement in the growing area. The long term solution is to increase the amount of calcium the plants are getting. Plant use calcium to build strong cell walls that can resist disease, especially fungus. Fertilizers often don't have enough calcium because the manufacturers understand that most soils and most water supplies contain sufficient amounts of calcium. But we don't grow orchids in soil and some water supplies don't contain enough calcium, especially if you use rain water or some other pure water source. I had big fungus problems each summer and often lost several orchids to different types of rot. I started using a calcium supplement about 4 years ago and now I seldom see any fungus, although it is possible to still get an isolated case. There are several ways to increase calcium. I use a calcium/magnesium supplement called MagiCal, that I add to my fertilizer every time I fertilize. Hydroponics stores carry cal/mag supplements. You can also top dress the pots with dolomite lime, crushed oyster shells or some other calcium rich product. Calcium will only affect the new growth so it takes a couple years to produce strong, fungus resistant plants. Good luck.

[orchidsarefun]

Further to Tucker's comment - if you have plant where rot recurs, it's best just to toss. I struggled for years with a zygo and a catt until I tossed both and have never had a problem with any plants again.

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[orchidsarefun]

Silje - have you tried hydrogen peroxide 3% ? Just water the plant with it neat. Roots may be affected but you may be able to save the plant.

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[Silje]

Originally Posted by orchidsarefun

Silje - have you tried hydrogen peroxide 3% ? Just water the plant with it neat. Roots may be affected but you may be able to save the plant.

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Should I just pour it over the plant as if I'm watering it with normal water?

[orchidsarefun]

That's what I have done in the past. Try it on 1 or 2. GL

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[Leafmite]

I am so sorry to hear this. I had this happen some years ago (I refer to it as the Black Plague). I lost many very nice Cattleyas (including one that I would REALLY love to replace), a Brassavola and some other nice orchids were lost. It does move very fast through the plant/collection and it was a very stressful nightmare. I eventually sprayed all the remaining orchids in isopropyl alcohol to disinfect them (twice a day for a few days), after cuting off all the growths that had even the slightest sign of it. After another day or two, the sad affair was at end.

At the time, there was nothing on this concerning orchids but my experience with other plants hinted that it might be Calcium deficiency so I started adding eggshells (as I was taught with my herbs) and I haven't had a problem since. I also grow all of my orchids on top of the medium and I don't spray any of the orchids.

I really feel for you. I know what it is to go through this and lost many, many orchids all at once, all very quickly.

[estación seca]

Look down to page 3, Water Mold, in this PDF found on the Web site of the St Augustine Orchid Society:

Orchid Disease Control, Sue Bottom

And here is more information on this group of infectious organisms. It deals specifically with propagating azaleas but the information is applicable to any plant:

Ohio State University Extension - Phytophthera

Also, 5% relative humidity and 38C will not harm your plants much. I would quickly put them someplace (in the shade) where they dry out as fast as possible. Water mold is spread from plant to plant by water. Don't allow any splashing and no spraying. Hydrogen peroxide is going to be your quickest aid.

{Edit 2016 October 01: The Ohio State Extension page referenced above is gone. I saved it, but can't find it anywhere on the OSU Web site. Here is the extracted text regarding fungicides:}

Some of the effective fungicides for Pythium and Phytophthora root rot diseases include Subdue MAXX, Chipco Aliette, Banrot, and Truban. Fungicides such as Domain, Topsin-M, Cleary's 3336 (thiophanate methyl), Banrot, and Terraclor are used for Botryosphaeria, Rhizoctonia, and Cylindrocladium. Cleary's 3336, Domain, Topsin-M, and Terraguard are excellent fungicides for control of Thielaviopsis black root rot. Mancozeb (e.g., Dithane or Fore), chlorothalonil (Daconil Ultrex), Chipco 26019, and Spectro 90 (thiophanate methyl and chlorothalonil) are excellent broad-spectrum fungicides for control of leaf spots that need to be applied weekly during mist propagation on crops such as rhododendron. Be sure to follow all instructions on the label. The best procedure is to alternate fungicides with different modes of action.

[Silje]

Originally Posted by estación seca

Look down to page 3, Water Mold, in this PDF found on the Web site of the St Augustine Orchid Society:

Orchid Disease Control, Sue Bottom

Yes, this is the link that I was referring to in my OP, actually. The problem is just that I struggle to get hold of the chemicals they suggest and I live far from the nearest outlet where I might get hold of them.

---------- Post added at 06:11 PM ---------- Previous post was at 06:09 PM ----------

Originally Posted by Leafmite

I am so sorry to hear this. I had this happen some years ago (I refer to it as the Black Plague). I lost many very nice Cattleyas (including one that I would REALLY love to replace), a Brassavola and some other nice orchids were lost. It does move very fast through the plant/collection and it was a very stressful nightmare. I eventually sprayed all the remaining orchids in isopropyl alcohol to disinfect them (twice a day for a few days), after cuting off all the growths that had even the slightest sign of it. After another day or two, the sad affair was at end.

At the time, there was nothing on this concerning orchids but my experience with other plants hinted that it might be Calcium deficiency so I started adding eggshells (as I was taught with my herbs) and I haven't had a problem since. I also grow all of my orchids on top of the medium and I don't spray any of the orchids.

I really feel for you. I know what it is to go through this and lost many, many orchids all at once, all very quickly.

So sorry to hear that Leafmite. I don't wish this on any orchid lover. This is really sad...

BUT, alcohol and hydrogen peroxide is available. I will try both of them and hopefully get this thing stopped before I'm orchidless. Thank you.

I just have say, one more time, it's CRAZY how quick it spreads and how fast the plant rot!

[estación seca]

This rot is a threat to your farm as well if you grow plant crops. Hydrogen peroxide is likely to work as well as any of those chemicals. None of those chemicals will enter a sick plant. The peroxide will kill the organisms on your growing surfaces and to some extent in the medium. I would consider to unpot them all, throw away all the media someplace where it will not enter the agricultural system, treat all the plants roots and tops with hydrogen peroxide 3%, allow to dry, then repot a few days after the infestation has been controlled.

---------- Post added at 11:45 AM ---------- Previous post was at 11:17 AM ----------

I would suggest everybody read the Ohio State link I provided earlier. Here's another, a presentation:

Huang Tze-chungBlack Rot Of Orchids Caused By Phytophthora Palmivora | Download PDF

I looked into Pythium when both First Rays and Carter and Holmes had fungicide on sale this past weekend. I discovered some but not all fungicides control Pythium. Some beneficial soil organisms do kill it. Some strains of Pythium are becoming resistant to fungicides. The State of California appears to permit some strong fungicides on "organic" food crops.