My Blueberry Plant Stems Have Black Spots

Sooty Blotch

• Black spotting on the stems of your blueberry plant could be sooty blotch, a common condition in blueberry plants. The organism that causes it works its way just below the surface of the stem. The worst damage that sooty blotch can cause is cosmetic. It does not appear to damage the plant and there is no need to try to eliminate it, according to Michigan State University.

Fusicoccum Canker

• If your blueberry plant is infected with fusicoccum canker, cankers will begin to appear along blueberry stems. Although the cankers themselves are not black, they develop black spots that produce fungal spores. The disease affects blueberry plants in the U.S. and Canada. As the it worsens, stems may wilt and die back. A fungicide in conjunction with pruning back affected stems should get the problem under control. To prevent a serious case of this canker, check plants regularly, prune away diseased areas, and dispose of the infected prunings away from the plants.

Phomopsis Twig Blight

• Phomopsis twig blight on blueberry plants is a fungus that causes cankers along the stems. At first, cankers are brown and over time they can take on a gray coloring. The cankers are not perfectly circular, but stretched out to as much as 8 inches on older stems. They develop tiny black spots as spores are produced. Water the plants regularly, and protect them from harsh winter frosts to reduce the danger of this twig blight. Use a fungicide and prune diseased tissue on plants that are infected. Dispose of the infected tissue away from the uninfected plants.

Coryneum Canker

• Coryneum canker in blueberries is limited to southeastern New England, according to University of Connecticut Integrated Pest Management. The fungal infection is more likely to occur if blueberry plants are injured or stressed by cold weather. Any wound in the stems of the plant creates an opening for infection. Coryneum cankers are similar to the other types of cankers. Prune out and dispose of diseased stems and then apply a fungicide to the plants to control coryneum canker.