Oiled paper wraps impregnated with copper compounds have been used for over 30 years to prevent the spread of gray mold rot in packed pears (see Pear Gray Mold Rot). Under normal conditions these wraps do not cause copper injury. But if the fruits are packed while wet, or if they are allowed to sweat in the boxes, small amounts of injury may occur. Copper injury symptoms appear as small black spots up to 1/16 inch in diameter at the lenticels. The amount of injury may range from a few scattered spots in slight cases to the involvement of a whole side of a fruit with coalescence of some spots in severe cases (see photo).
Copper injury can be prevented by packing dry fruits only, and by preventing the alternate cooling and warming of the fruits that causes sweating.
Pear copper injury