Chalkbrood disease of honeybees is the most common brood disease found in Minnesota. The disease is caused by the fungus Ascosphaera apis. Chalkbrood is most common in colonies which are stressed by factors such as poor weather, low colony population, American foulbrood, or mite infestation. There are no medications available for treatment.
Treatment consist of dealing with stress factors that the colony is facing, requeening with more resistant stock, and removal of sources of spores from the colony.
If American foulbrood is present a good treatment program using terramycin is needed. Colonies infested with tracheal mites should be treated with menthol in May. If varroa mites are found, treatment with Apistan strips should be done. If stress is caused by lack of pollen feeding a pollen substitute may be helpful. None of these treatments can be done when honey supers are on the colony.
Requeening can be effective if you can get a queen from different, more resistant stock. The cleaning behavior of the workers is important in resistance to chalkbrood. If the workers remove the mummies from the hive quickly, they can contain the infection. If you find combs with many mummies, the bees are not cleaning the hive effectively and you will want to requeen.
Clean all mummies off the bottomboard. Chalkbrood spores remain for many years on the combs so you will want to remove and destroy heavily infected combs.