This is a hirsutissimum that has been slowly yellowing. All the plants around it seem happy enough. But based on the water report from my city, I thought the yellowing may be due to insufficient nutrients. Nitrates and nitrites combined are <0.30, Cal/MG 18/1.9, orthophosphates <0.01, pH 8.3. While I am waiting for new fertilizer to arrive I went on and added Cal/Mg and phosphoric acid to my water. Within about six hours I noticed this spot. There is nothing on the underside. It smells of fermenting cider. Something I did to the water? Erwinia? And if so, physan 20 or phyton 27. I am worried about phytotoxicity with the 27. I have on hand copper octonoate. Will this do anything? The plant is already in quarantine. Appreciate any thoughts on this.
Yikes, spotted leaf, erwinia?
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Hmm... not sure if this is Erwinia or not but my Paph mentor -- Faan Kruger -- told me to take a pin, heat sterilize it and then puncture the spot to allow air in and that would stop the spread. Worked every time. I now do one better, and after puncturing the whole spray the plants down with 3% hydrogen peroxide.
Good luck
Good luck
Thank you. I had read about using hydrogen peroxide but I didn't know the concentration. If I can bother you with two more questions... My peroxide is already a three percent solution. You don't dilute that to 3%, do you? And do you soak the medium as well? Thanks for your help!
Hello, I spray directly onto the plant. Soaking would not be a good idea as it could kill the mycorrhizae fungi and that would kill the plant. The peroxide is a surface sterilizing but you will see how it fizzes over the pin prick and does seem to penetrate where the leaf integument is damaged.
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I believe that the recommendation for use of drugstore 3% hydrogen peroxide has been passed down from since before much was known about its interaction with plants.
Such products are typically weakly stabilized with stannous chloride. Upon contact with metals or organics, the energy release is sudden and extreme, so can damage root hairs that play a significant role in nutrient uptake, and leaves behind a puddle of water that, under the right (wrong?) conditions, can be a new incubator for pathogens.
More recent work by Biosafe Systems has led to peroxides stabilized with peracetic acid, and they have the advantage of a very controlled decomposition that shows no phytotoxicity and remains chemcially active until it dries, making it a more effective treatment.
I retired from the largest producer of hydrogen peroxide in the world, and some of our marketing folks complained all the time that the Biosafe patent position prevented us from entering the plant-centric market.
Such products are typically weakly stabilized with stannous chloride. Upon contact with metals or organics, the energy release is sudden and extreme, so can damage root hairs that play a significant role in nutrient uptake, and leaves behind a puddle of water that, under the right (wrong?) conditions, can be a new incubator for pathogens.
More recent work by Biosafe Systems has led to peroxides stabilized with peracetic acid, and they have the advantage of a very controlled decomposition that shows no phytotoxicity and remains chemcially active until it dries, making it a more effective treatment.
I retired from the largest producer of hydrogen peroxide in the world, and some of our marketing folks complained all the time that the Biosafe patent position prevented us from entering the plant-centric market.
Thank you both for the detailed and super informative information.
a paste of mancozeb applied to both sides of the spot.
Thank you for the info. House guests at the moment so everything on hold for a bit. But no more spots have appeared. 
Tom499
Well-Known Member
Thank you! Such great advice - done this on a young paph that had an infected leaf and after puncturing the area has dried right up!
