Came across this: You take a 1 1/2′ shim board and put it on your hive. Then you take a banana cut it in half and put it on the top bars inside the hive, skin down. Leave your hive alone for one month. Do not peak! One month later the banana will be dried up and the Chalkbrood will be gone.
http://www.beverlybees.com/mass-bee-field-day-2012/