Pear decline has occurred predominantly with rootstocks of two oriental species, Pyrus serotina and P. ussuriensis, although there have been reports of tree losses with P. communis rootstocks. Most of the latter have been of the “old” French type imported from Europe prior to 1918. While decline has occasionally been suspected with additional types of P. communis rootstocks (domestic French), generally this species has been tolerant to decline. Although certain seedlings of P. communis have frequently been referred to as resistant or immune, some uncertainty now prevails regarding such resistance. Diagnosis of decline often has been made without microscopic examination of bud unions, and even when bud unions have been examined for phloem abnormalities, the identity of the rootstock may be open to question.