Q.split leaf philodendron
My split leaf philodendron grew fairly fast and looked very healthy last summer. Then in the fall, two lower leaves turned yellow, one by one, and the new leaf looked stunted and turned brown. I noticed white blister-like spots on the main stem, upper area. The plant is growing yet another leaf; however, it is smaller than the others. What is bothering or even killing my lovely plant? This is a houseplant.
Yellowing and dieing of old and new leaves is possibly a sign of fungal infection in the roots, often called root rot, most likely caused by over-wet soil. A fungus would also account for whitish blisters on the stem. Philodendrons indoors, especially if they are in only moderate light, need to have the soil get almost dry all the way to the bottom of the pot between waterings. Probably what happened is that when the light level reduced as fall approached, you continued to water the same as you did in the summer. You need to reduce water when light gets less. Checking soil moisture with an electronic meter should be helpful. https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm
