Fungus? Bacteria? Virus? Nothing to worry about?

Orchid Doctor

by John Small

In 2015, after a 15+ years hiatus, I got back into growing orchids. I had a nice combination of hybrids and species, cattleya and oncidium intergenerics, about 125 plants. Suddenly, everything began to turn black, leaves, old and new pseudobulbs, and plants began to die. No one seemed to know what it was and nothing worked to stop it, not Thiomyl, not Dithane M45. I threw away everything but three plants -- a Pot. Love Triangle, a Catasetum Donna Wise and a Neofinetia falcata that didn't seem to be affected. I moved to a new location where I couldn't grow orchids because of no light and intense heat on my patio, so I left those three plants on the patio and forgot about them. About a year and a half later, I remembered they were there and hung them on the fence around my patio, on the north side. Amazingly, they all came back, but soon the Love Triangle began to turn black. I took it to The Mounts where the cause was identified as Lasiodiplodia theomobrae. Nothing saved it, Daconil, and another systemic fungicide/bacteriaside couldn't even touch it. I now have about another 125 plants, some hanging on my fence, some hanging on pvc pipes, some on racks I built for the phals and oncidiums and some in the two upstairs bedrooms, hanging from curtain rods, sitting on tables in pots and some in pots on the window sills. The other day, the leaves on my Blc. Orglades' Grand 'Tian Mu' began to turn yellow, then black. It had this incredible root growth, but that couldn't save it. I took it into the kitchen to isolate it from the others. It died there. The Catasetum Donna wise is okay, still growing, but not blooming (my fault) and the Neofinetia falcata is growing like a weed and should bloom this summer. This morning I saw these spots on my Blc. Hawaiian Wedding Song 'Virgin'. I want to make certain I'm not just being paranoid. It is beginning to look all too similar to what happened before. I hit all the plants on the fence Sunday morning with Thiomyl. Since it says on the label that it has systemic action, I poured a mixture pf 2.5-3 teaspoons per gallon over each plant. If anyone recognizes this and knows how to stop it, please contact me or respond to this posting. If my collection or half of it, gets wiped out, I probably will give up on orchids for good. Any help will be appreciated.

 

John Small

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  1. Carol Holdren
    2 months ago
    Googling the fungus name you provided, the fungus over winters on the outside of diseased wood. It says spores are released up to 2 hours after rain.
    1. John Small
      2 months ago
      Hi, Carol, Thank you. The people at The Mounts told me Lasiodiplodia theomobrae is a fungus that is water borne, not air borne, so that would fit with what you read. The only common denominator from where I lived before and where I currently live would be the three plants I brought with me and the hose I use to water my orchids. Of the three plants, only the Love Triangle exhibited the same symptoms as before and that was before I purchased any of the plants I now have. I left it on the patio and treated it with Daconil and something else. It died, so I don't believe there was any direct or indirect contact with the other plants. I could be wrong. The Hawaiian Wedding Song had three flowers developing within a sheath. Two have come out and seem still to be developing, while the third one turned black, so I picked it off. The other two have not yet opened and seem to have some markings on the back of what should be the dorsal sepal. I'm going to keep an eye on them. I was fertilizing with a combination of BGI Orchid Gain 13-2-13 and Better Grow Better-Bloom 11-35-15 at about what I believe was half the recommended strength. I was getting excellent root growth and then everything seemed to dry up. I did notice that two of the three new growths on Hawaiian Wedding Song do tend to droop a bit. I since have cut back even more on both the quantity and frequency of fertilizing. I have been alternating between Thiomyl and Dithane M45 the past couple of weeks and zapped the plants with some Superthrive, half teaspoon to two gallons of water. I do have a purpurata werkhauserii that I cut the bad stuff away and have it sitting without media to see what happens. If The Mounts were open, I could take one or more of the plants there. I will check for that book online. Luckily, I got most of my good stuff after I noticed this, so they are upstairs and have not been exposed to any of the plants on the fence. I guess I'll just have to keep at the with the fungicides and hope for the best. John
  2. Carol Holdren
    2 months ago
    Hi John, Since no one has answered your question let me ask one of the professionals and get back to you. An orchid friend did tell me they thought it was fungal. But let me ask and then I will post the answer. My best guess is that it is fungal & I wonder what you are fertilizing with (maybe too much growth & too soft) and if you use any type of calcium. When I have black rot I take the plant out of the pot & cut back until all of the rot is gone. Then I let the orchid sit w no media, waiting for some root growth. This works since I am in a warm & humid area. I do spray the cut & roots w fungicide. I looked in the AOS book, “Orchid Pests and Diseases” but saw no obvious comparison. I highly recommend the book which can be purchased several places. Carol
    1. Lou Lodyga
      2 months ago
      John, are the lesions moist or dry on your plants?
      1. John Small
        2 months ago
        I have a C. Bob Betts that has some dry lesions on one of the new pseudobulbs, but I think that might be because a plant hanger from another plant was rubbing against it in the wind a week or more ago. The plants that are turning black and dying I would have to say are moist and soft. I have seen the St. Augustine society's page, but I never printed a copy of their information. I think it is time to print a copy and read it. Thank you, Mr. Lodyga. I have heard your name many times in the years I have been growing orchids and I know that you are very well-respected among longtime growers. I've known Carol for many years, when we both were members of the Deerfield Beach society. I appreciate you and Carol taking the time to respond. John
      2. Lou Lodyga
        2 months ago
        Here is a good link to refer too using the various pesticides and what they are good for. https://staugorchidsociety.org/PDF/OrchidPestsandDiseasesbySueBottom.pdf

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