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This is a discussion on Black fungus on roots of Phal and others within the Orchid Ailments / The Compost Pile forums, part of the Orchid Culture category; Yikes! I have been fighting a black fungus (I assume) on the potting mix of ...
Yikes! I have been fighting a black fungus (I assume) on the potting mix of my Oncidium Sherry Baby. It just migrated to my most prolific Phal, which has been in bloom since last July. To this point, I've used a mixture of rosemary oil and wintergreen oil, but it clearly has not defeated the foe. I just increased the humidity in my growing area, and now it appears to have migrated to the surface of my Phal. Any tips for removal? Is it a harmful fungus other than aesthetically? One suggestion that I've heard is physan-20. What do you think? for reference, I've attached a pic of the nasties.
That is either a fungus or an algae, possibly caused by overwatering or keeping too damp. I would pull the plant from its pot, soak the pot in hot water then some copper oxychloride, then soak the roots in some copper oxychloride too. Remember for the soaking part, mix about 1 part copper (liquid or powdered) to 3 parts water. After you have repotted with fresh bark, carry on with a regime over 6 weeks of spraying weekly with a quarter strength copper oxychloride solution. Then after this, start fertilizing weekly, weakly with a proper orchid fertilizer. Never mix copper oxychloride and orchid fertilizers, i did that once and it killed the plant.
I wouldnt take any risks, and i would check to see if there is any root damage down below.
Good luck! Jordan
Thanks for the tip. Note that this fungus is a new arrival on the Phal. It's been wonderfully healthy until a few days ago. The problem is its neighbor, the Oncidium. I think I will apply your suggestion to it. I've been dissatisfied with its health for a while, doing less invasive fixes. Since it has become a vector, it will get the more invasive treatment. Thanks for the suggestion. I think I have the copper oxychloride around already.
I use one called Champ DP and it is about 1x more strength to it. I use this in halved quantities to the specified amount of water (ie: one teaspoon to 5L = half teaspoon to 5L) Just a guideline i suppose
Better repot. If it is staying damp enough for that type of algae to grow, the roots are probably either damaged or will soon be. Take it out of the pot and wash the old medium away with a water hose or in a utility sink with a sprayer. (Just be sure to clean up the roots completely.) Then let it sit and dry-off out of a pot. Overnight is fine for the time out of the pot. The next day, soak the roots until they turn green and then repot in a clean pot with fresh mix.
Update. I pulled the sherry baby out, gave him a good long soak in the fungicide, and found that his roots are still very healthy, albeit a little overcrowded. After teasing the old stuff out, he went back into a slightly larger pot with just medium fir bark, with which I've had a lot of success. We'll see if the stress robs me of a blooming season, since I have two growing PB that were next in line for spiking. Even so, I had grown tired of the fungus and he's no longer a vector. Thanks.