Garden Pests and Diseases: Begonia fungal infection, 0 by nomosno

nomosno wrote:
This plant is the successor of a large and heavily infected cane begonia, found in a dark hallway thrown away by someone. It was thickly covered with some fungus. I cut it up into small pieces and regrown it from rootings. Now it lives in a backyard in San Diego near the ocean. Every time there is a period of constantly overcast weather, which is usually during May-June, it redevelops the same fungal infection. A white, powdery substance covers the stems but the leaves remain free of fungus except that they eventually drop off and the branches are bare except the newest leaves on the tips. Flowering goes on for a long time, even when the leaves are falling off, even tho the efflorescences are not as big as when the plant is healthy. The plant does not die, or at least I have never let it die, eventually, when I realize what\'s going on, I start spraying it with a fungicide form Home Depot. It seems to be partially effective. Once the sunny days are here the plant becomes fungus free, at least outwardly.

So I have 2 +1 questions:

1: What is the best fungicide to deal with this infection?
2: Is there a way to kill the fungus in this plant once and for all? For instance I though about creating fungus-free plants by soaking the cuttings in water that has fungicide dissolved in it and then growing them out.

The +1 question: can someone identify this begonia?