It's not black rot...what is it?

[lauraads]

I have a very nice collection that I pay very close attention to for problems. I make sure to water early in the day, have a fan blowing for circulation, treat with thiomyl systemic, etc.

Since winter (January) I've seen some disturbing symptoms that have had me losing about a dozen orchids now. I brought leaves to a local chapter meeting and they said 'that's from it touching the plastic of your poly wrapped orchid house when it was freezing outside'. Then when it continued to happen long after it has warmed up here in FL to ones not on the edges of the grow house, the response has been, 'that's black rot'. But, it has no odor and is not mushy, and never responds to being treated as black rot.

I talked to several growers at a recent show and tried their varying advice.

I have treated as black rot - one recommendation was to cut back to green growth, remove plant from pot and discard all potting materials/pot, steep plant in thiomyl solutions for 20 minutes and then three days later pour peroxide on it, then three weeks later repeat thiomyl. Except, I'm not making it to the 3-week treatment as all the leaves will have turned black and fallen off by then. I also used SA-20 on a few plants previously - also unsuccessful.

Shown are photos (front/back) of a pair of leaves on my C. Maui Plum Volcano Queen. This plant was cut back and treated about 10 days ago week with thiomyl and then peroxide about 7 days ago. The white on the leaves is from thiomyl. Just as I thought we had survived, two more leaves started turning black at their bases and fell off. Now it has only one set of leaves left and I know it's a gonner.

I do isolate the plants when I see this happen.

Any ideas? This is so distressing. I've lost one really rare orchid so far and others I love as well. I just don't know what it is and can't seem to stop it.

[lauraads]

I've spent the morning not working and looking for images and advice online for what this might be. While it doesn't smell like it and hasn't responded to treatments, I just can't imagine what else it could be. I wish I had prior photos to show you but when I look at the many photos on line when Googling 'black rot in orchids' all those that start at the crown on Cattleyas look like what I have with the blackening, yellow of leaves, dropping of leaves.

SO - does anyone have any other ideas for treating black rot?

Thank you!

Laura DeCarlo

[lauraads]

I took a look at the book Florida Orchid Growing by Martin Motes and viewed his recommendation for Black Rot. The short version is five applications from May - Sept of BANROT 40WP (Etridiazole plus Thiophanate-methyl). He lists these as two items - Banrot and Thiophanate-methyl. But, I found a company that sells the two together as Banrot 40WP. I purchased a 2-pound bag for $113 + shipping and will see what happens.

Other suggestions I saw online were to use Aliette and Motes does suggest Aliette in place of Banrot with the thiphanate-methyl. One $100+ purchase at a time, however.

I probably won't know the outcome for quite a while, but fingers are crossed.

Again, if anyone has any ideas, I would still like to read them!

Thank you.

Laura DeCarlo

[lauraads]

After I placed my order for Banrot I was sitting in the passenger seat of the car taking more time to read and realized that it said Banrot did not work quite as well as Aliette. Sigh. So, I called JR Johnson where I ordered from in MN and am purchasing Aliette and Thiophanate-methyl separately. They sell generic versions. Whew. I pulled four Catts out of the collection today with the black on the leaves and just feel so sick about it.

I think I know where the infection started. I'm not going to type a company's name here but theirs was one of the first orchids I lost bought at a show in Miami earlier this year. I actually replaced that plant with them at Redlands last week. I missed the black on two of the leaves - it wasn't near the crown like my others but in the middle of the leaves (big plant and I was too excited at replacing, I guess, to really inspect and make the connection). But, from my research today I see it is the same thing. So, obviously I just paid more $ to bring another infected plant home from the same grower. I feel stupid for getting excited about finding it and not knowing better / connecting the dots.

I just hope learning does not cost me too much of my so loved collection.

Laura DeCarlo

[EdM-in-TN]

Laura, what your plants have looks like a fungus infection. Typically, areas of plant tissue that turn yellow and then black, and spreading, are fungus infections. Bacteria infections typically turn brown and watery with an odor. Treat the two types distinctly differently. You should try a systemic fungicide for the affected plants and a topical fungicide, like Mancozeb, to act as a preventative.

[lauraads]

I will definitely try that out. At this point am covering the bases! I think I've been lucky to not have problems before with my collection. Looks like they sell Mancozeb at Ace Hardware, so readily available.

I did try a biological fungicide before reading this this weekend (and have used thyomil without luck). We'll see!

Thanks again!

[bobwhiteside]

the use of any fungicide or bacteriacide will not resolve the black spots on the leaves. all they will do is prevent the transmittal of the disease to other plants and stop the progression on the infected plants.

With a sterile razor blade, cut the infected leaves well below any area of infection and treat the cut edge with either cinnamon or hydrogen peroxide. My preference is peroxide as it is much easier to use on a cotton ball or q-tip. You need to cut past all the yellowing areas as this is areas the disease has started to infect. From the looks of your pics, you may lose several of the leaves all together.

Good luck