Find Your 
In this up-close photo, you can see the gray spots that are appearing on several of the dieffenbachia leaves. From the picture the gray spots look more like a burn rather than a fungal problem. Must fungus will have a halo appearance instead of a monochromatic spot. The fungual spot usually has a reddish or brown center and a yellowish halo. See pest & diseases associated with dieffenbachia.
This information provided by Flower Shop Network.
I’m not sure this space is meant for questions, but here goes: I am forwarding a picture of my dieffenbachia plant. I have had this plant for over 6 months, and upon purchase it was large, healthy and thriving. According to another website on dieffenbachias, it was a “fat and very content” plant, as it constantly dripped clear fluid from its leaves. We moved to a different house about a month ago and the plant got slightly damaged enroute. It lost one leaf and another was split. Since then, it appears increasingly unhealthy. There is a brown lesion type of mark in the centre of one of the leaves, and “cut-like” marks on several other leaves (that did not happen on the move…they just appear). I have recently removed a leaf that browned and yellowed until it wilted. Another large leaf is following suit. The plant did well receiving direct sunlight (western exposure) in my last home, so I have put it our south-facing bedroom bay window. Is my plant dying? Any comments or recommendations would be appreciated. Thanks :-)
Attached Image: IMG_5699.jpg
Most likely your plant is just trying to recover from the shock it went through during the move. It takes some time to get over the stress, but your plant should perk back up with good care. Some things to check for though, 1) make sure your plant is away from vents and drafts. 2) the humidity of your new house may be different from your old; keep your plant misted and properly watered. Dieffenbachia enjoys a warm and humid environment. Be careful to maintain a warm, evenly moist environment, as plants kept too cold may experience excessive leaf drop. Water regularly with lukewarm water. Allow tap water to stand until room temperature. This will allow heavy toxins such as chlorine to evaporate while preventing root shock in younger plants. Mist daily in summer and water sparingly in winter. — With care, your dieffenbachia will be fit as a fiddle in no time! Good luck! Hope this information was helpful.