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You are here: Experts > Style > Gardening > Orchids > Cymbidium black spots, mottling leaves
Orchids - Cymbidium black spots, mottling leaves
Expert: Wayne King - 11/4/2009
Question
Hi Wayne,
I have a Cymbidium Chung Ruby orchid and recently noticed it had a few larger black spots near the base of one of the new developing shoots. I then noticed that on the base of one of the older pseudobulbs, a much larger black spot has developed.
I'm worried I'm going to lose the poor plant. I bought it as a tribute to my father that had passed away less than 2 years ago, as it was one of his favorite orchids. I'm starting to think I'm terrible with them - I've already lost 2 plants.
I'm noticing now that the leaves of the younger shoot are getting increasingly mottled and are yellowing. I'm not sure what I can do - but didn't want to do anything until I asked you.
Please help! I've included pictures here. Since I had originally taken then, the leaves are already more obviously mottled and seem to be getting more light-green/yellow by the day.
Answer
Vivian, thank you for seeking my advice. You didn't mention any repotting that might have been done recently. Most orchids, depending upon the type of potting mix used, should be repotted annually. If this is not done, the roots can suffer, the potting mix in the lower part of the pot may have decomposed and, as a result. may stay too damp. This constant dampness can cause root rot and fungus growth which may manifest itself with the blackened areas at the base of the plant closest to the potting mix. I recommend a two part process. Obtain a bag of fir bark based orchid potting mix for repotting your plant. Then, unpot your plant, remove any infected sheaths such as those covering the pseudobulbs, and rinse off the roots. Locate a copper based fungicide such as Kocide and mix up a solution at the recommended dosage. Make enough so you can submerge the roots and base of the plant in it. Be sure, first to remove any roots that are stringy or have lost substance (healthy roots are firm). Let the plant base and roots rest in the solution for an hour and then lay it aside on some papers to dry out. Be sure to use chemical gloves in handling the solution and plant soaked in the solution. Clean the empty pot thoroughly or use a new pot as fungal spores could be present to reinfect the plant. Normally I recommend soaking the potting mix prior to use but, in this case, I recommend using it dry. Once the plant and roots have dried, you may repot it. The copper fungicidal solution will leave some green staining on the psrts of the plant exposed to it. That not only enables you to see the parts exposed to the fungicide but the residue can serve to prevent further infection. The fungicide will not change the damage that already has been done but will prevent the spread and allow new future root and shoot growth to be normal.
I recommend that you water once per week using the left-over fungicide solution until it is gone. Then you can resume normal watering at once per week and, when new growth appears, also begin feeding the new growth.
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