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Root/collar rot (Phytophthora cactorum, Phytophthora spp.) is first noticed by aboveground symptoms. Stunting or unhealthiness of trees may begin with small yellow leaves that turn reddish-purple later in the season. Cankers develop at the soil line but may not be noticeable without removal of bark. Bark may be dark-colored and soft, and underlying wood is reddish-brown and often slimy. This decay girdles trees, and trees often die within 1 to 3 years. Infections are more widespread and lesions develop more rapidly in damp, saturated soil.

Collar rot symptoms aboveground (Longstroth, MSU)
Collar rot symptoms aboveground.

(Photo: Mark Longstroth, Michigan State University)

Collar rot symptoms on young tree (Longstroth, MSU)
Collar rot symptoms on young tree.

(Photo: Mark Longstroth, Michigan State University)

Collar rot trunk canker (Longstroth, MSU)
Collar rot trunk canker.

(Photo: Mark Longstroth, Michigan State University)

      

Management:

  • Site selection (well-drained soil or improving drainage)
  • Disease-resistant rootstock

      

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