Recently, an AGGA member grower reported that their poinsettias had colored beautifully but the leaves were turning yellow, dropping off and show other symptoms as well. The grower tried to diagnose the problem by looking at resources on websites, and applied both magnesium and iron. Finally, Dr. Mirza was called to help.
After examining pH, EC values, fertilizers, watering schedules, day and night temperatures, the answer was provided by the last picture where the heating furnace of 250,000 BTU was not being supplied with fresh air for combustion. Mainly it was ethylene gas as product of combustion that appeared to be causing leaf drop. Grower was told about the importance of bringing fresh air near the combustion chamber.