Blueberry Plant Diseases

Types of Diseases

• The diseases classified as rots are the most numerous to afflict blueberries. Cankers are also a problem, as are leaf diseases, blights, ringspot diseases and other miscellaneous diseases. Most of the common blueberry diseases are fungal. Halt or prevent some of them through the use of fungicidal products that you spray on the plant, but fungicides do not work on all blueberry fungal diseases. Keeping your plants healthy is the best preventive medicine.

Rots

• Rots are serious diseases that can affect blueberries' growth and fruit production. Included are Alternaria leaf spot and fruit rot, Anthracnose fruit rot (ripe rot), Armillaria root rot, Botrytis blight and fruit rot, Cylindrocladium rot, Phyllosticta leaf spot, fruit rot, berry speckle, Phytophthora root rot, post-harvest fruit rots and ripe rot.
  General guidelines for controlling the rot diseases include spraying a fungicide periodically after buds form until harvest time; pruning old or infected wood; planting varieties that are resistant; refraining from watering overhead; harvesting promptly when fruit is ready to be picked and cooling the fruit quickly immediately after you harvest.

Cankers

• Cankers are stem diseases that can cause minor to significant damage to blueberry stems. Cankers include bacterial canker, Botryospaeria stem canker, Fusicoccum canker and Phomopsis canker and twig blight. Botryosphaeria stem canker presents a serious problem for blueberries in the southeastern United States. Bacterial canker occurs primarily in the western U.S.---it often does not present major problems.
  To prevent cankers, plant resistant varieties and prune diseased stems in summer; do not apply nitrogen fertilizers in late summer; give blueberries a dose of copper in the spring and autumn; protect plants from frost burn and sterilize clippers and other tools before and after you use them on blueberries. Fungicides are not effective on all cankers.

Leaf Diseases

• Diseases that affect blueberry leaves include Exobasidium fruit and leaf spot, leaf mottle, leaf rust, various leaf spot diseases, red leaf, ringspot, tomato ringspot, necrotic ringspot and red ringspot.
  Exobasidium fruit and leaf spot causes small green spots on leaves and berries after the plant flowers. Leaf mottle is a virus found in Michigan that can present serious problems with the mottling pattern it causes, which can make leaves misshapen and unhealthy.
  Control leaf diseases by planting resistant varieties, pruning to improve air movement and destroying infected plants. Fungicides can help some of the leaf diseases.

Blights

• Blights are sometimes called diebacks, as they cause stems and branches to turn yellow, dry out and eventually die. Blights that can affect blueberries include twig blight, Botrytis blight and Botryospaeria stem blight.
  Twig blight occurs almost everywhere that blueberries grow: it causes rapid wilting and then death of branches. Botrytis blight is usually a minor disease but can cause blight on the blossoms and the fruit to rot. Botryosphaeria stem blight can be very destructive in the southeastern United States.
  To control blights, plant resistant varieties; do not overhead water; use sterile planting material; prune infected branches below signs of disease and then destroy them. In general, fungicides are not effective.

Other Diseases

• An assortment of miscellaneous diseases can cause problems for blueberries. These include crown gall, dodder, mosaic, nematodes, powdery mildew, scorch, shock, shoestring, sooty blotch, stunt and witches' broom. Crown gall is rarely seen in mature plants. Dodder is a flowering plant that parasitically attacks blueberries. A virus is suspected with mosaic, which causes leaf mottling in mosaic patterns. Nematodes are soil-borne roundworms that do not ordinarily cause problems for blueberries, but they can carry viruses that can attack the plants. Witches' broom is usually a minor disease that affects high bush blueberries.
  Control of these diseases is similar to control of the other diseases: plant resistant varieties; do not overhead water; use sterile planting material; sterilize tools; prune infected branches below signs of disease and then destroy them. Fungicides are effective against some diseases, but check with your local nursery or Agricultural Extension Service for details.