Answer: Dieffenbachia can fall prey to stem rot disease if the plant is overwatered and experiences low air temperatures. It's best to cut away the diseased stem and correct the conditions that allow the problem to develop.
Provide average to above-average household temperatures (a minimum of 60F in winter), bright light, and regular water during spring and summer (water sparingly in winter). Try to keep water off the base of the plant by applying water to the soil, not the plant. During active growth mist the leaves occasionally to increase humidity around the plant.
Hope your plant regains its health!
Q&A Library Searching Tips