Phytophthora root, crown, and collar rot
Disease
Phytophthora root, crown, and collar rot
Phytophthora cactorum (Lebert & Cohn) J. Schröt.
Distribution: Common to all fruit-growing regions in eastern North America.
Photos
Infected tissue often shows a clearly delineated, reddish-brown discoloration of the inner bark several inches below the soil line.
Thomas Burr, Cornell Univ.
C
Crown and collar rot are often and mistakenly used interchangeably. Collar rot refers to infection that affects the bark tissue of the scion portion of the tree at or just below the soil line, whereas crown rot affects the bark tissue of the rootstock portion of the tree. Infected trees often have a normal bloom, but developing fruits tend to be small, the leaves wilt and drop, and the tree shows a general decline and eventually dies (A). Symptoms on apple usually develop over several seasons, becoming progressively worse. Apple, cherry, peach, and apricot trees are more susceptible to infection than pear and plum trees. Phytophthora-infected tissue often shows a characteristic reddish-brown discoloration of the inner bark several inches below the soil line with a characteristic, clear-cut margin of diseased from healthy tissue (B, C).