Calyx-end rot, caused by the fungus Sclerotinia sclerotiorum, is characterized by a small (~ 0.5 inch) brown lesion that develops at the blossom end of apple fruit. Disease symptoms have been observed in orchards in the northwest, west central, and eastern regions of Michigan on McIntosh and Honeycrisp. Up to 20 percent of fruit have been infected in some blocks. Rot symptoms usually become visible about one month after petal fall. The rot looks soft.
Symptoms are not associated with internal rotting of the fruit. The disease is associated with wet periods during bloom, petal fall, and early fruit set. Spores can be produced on infected fruit from the previous year or on any of several alternate weed hosts, including dandelion and wild clover. Because the disease is so sporadic and typically has not resulted in significant infection, there has been little justification for chemical control studies. It is possible that fungicides used for apple scab control may also effectively control calyx-end rot. |
 |
| Calyx-end rot on Honeycrisp apples. |
|
