Ok, I change my opinion to bacterial leaf spot. Apparently philodendrons are susceptible. It can spread quickly when the plant is not happy. Not enough light, too much water. Misting can make it spread. Instructions are to remove infected leaves unless it's the entire plant, then it cannot recover. I would hang on and see if another opinion comes along, because I am not an expert in philodendron and am not familiar with growing plants in mountainous areas. It may be a whole different ball game there, that I am not aware. Good luck :)

Copying here too for these people to think on as a possible cause (from my post about the same problem): @petrushka you actually just said something that kind of put me on to something else which is a way better problem to have than bacteria. Considering your dew drops... I have those too, but I live in super hot, humid, muggy, northeast Florida, so transpiration is pretty common here. That’s what your “dew drops” are- the plant is transpiring extra water through its leaves (kind of like sweat). The fact that you’re getting it in NY with the same spots makes me think it’s Edema (or oedema)- basically the plants roots are taking up more moisture than it needs, faster than it needs, and it’s causing some rupturing in the leaf cells. This prob has to do with finding the right balance between light, air circulation, soil, or proper nutrition (not having certain nutrients in the soil, or the plant not being to absorb them due to soil ph).... for ME. I think yours might be due to temperature. If it’s cool or cold there and you water with warm or tepid water, the difference in temperature can cause the edema too. Also. If you’re misting or using a humidifier, you prob don’t need to since that would just contribute to the transpiration. Let me know what you think!

Plant receives bright light throughout the day, i only water it thoroughly once the soil is slightly dried. What could be the cause of the yellow specks on the leaves? I have very closely inspected the plant for pests and found none. it has new growth which is healthy but starts getting specks over time. the plant is definitely not dying but the specks ar unsightly. Please help

If it makes things easier I will copy the text from the link above. Why does my Congo rojo have Yellow spots? Asked October 17, 2018, 11:41 PM EDTSave I received a transplant of a Congo rojo philodrendren plant. It recently has gotten yellow spots on the foliage. I'm not sure if this is normal or an abnormal. Any info helps, thank you! Kent County Michigan 1 Response Hello! I'm sorry it has taken such a long time for a response. This one has me a bit puzzled--not much bothers philodendrons, as long as they receive the amount of water and sunlight that they need. The yellow spots on the foliage are not normal for this plant. From the photos, they look like small, dry, sunken areas of necrotic (dead) tissue. Thrips cause damage like this, but I saw no evidence of these insects in the photos (the critters themselves, or their excrement). The pattern of damage left behind by thrips is also more concentrated, as they feed while moving across a leaf. Might anything--household cleaners or polishes, for example--have gotten sprayed on the leaf? This spotting could be a chemical burn, in which case you would simply leave it alone. Unless subject to additional exposure, these burns would not spread. Once additional leaves form, you could remove this one, if you find it unsightly. The other possibility is leaf spot, most likely caused by a fungal infection. Bacteria also cause leaf spot diseases, but the infected tissue is usually wet/slimy. If it's a fungal infection, it will likely spread across the leaf. If the plant had more leaves, I would suggest removing the infected one. Since it does not, and since the green areas of the leaf are still producing food for the plant, I would simply monitor its condition. Once new leaves develop, you can remove the infected one. You could apply a fungicide that is approved for use on indoor plants to new leaves as they develop. Regards, Becky Irey Replied October 31, 2018, 1:25 PM EDT Answered by Becky Irey This question is grouped with Michigan State University Extension Ask an Expert is made up of groups and individual experts. ASK A QUESTION