Question
I live in Franklin, TN and have been having trouble the last several years with a type of fungus that attacks the stems of my impatients. The stems turn black and wither at ground level and the plant wilts and breaks off. The stem is a blackish color and look dry. It attacks quickly without any other symptoms to the plant. I've tried spray on fungacide when the symptoms first appear but it dosen't help and it soon spreads to other plants. I've heard it could be in the soil but I don't know what to use. Any help would be appreciated.

Answer
This sounds like Rhizoctonia crown rot.  Rhizoctonia solani.
Infection first appears as a general decline, yellowing, and wilting of the entire plant. This is usually followed by complete collapse of the plant. Brown to black lesions can often be seen at the base of the stem, usually at the soil line.

Control can be difficult once plants are infected so prevention is important. It is helpful to avoid overwatering, especially in heavy soils, and to avoid watering directly into the crown area of the plant. Adequate spacing between the plants can promote good air circulation. Highly symptomatic plants can be rogued and removed since recovery is unlikely. Control can also be achieved with the use of fungicide sprays applied as soon as symptoms are visible. Among the compounds registered for use  are iprodione and thiophanate-methyl. Consult the label for dosage rates and safety precautions.