Exposure to ammonia fumes may injure pears. The trouble is first evident as reddish-brown rings around lenticels and at abrasions. When pears are removed from an atmosphere containing ammonia, the skin color soon changes to black (see photo). In mild cases, the injury does not extend beyond the tissues immediately beneath the epidermis. With more severe exposure, the lenticel spots may become much enlarged and finally coalesce, and the discoloration may extend deep into the flesh.
The presence of moisture is favorable to ammonia injury; Pears with moist surfaces are more susceptible than those that have dry surfaces. Immature pears have been found to be more susceptible than mature ones.
Pear ammonia injury