Fire blight

Fire blight is a disease that is very environmentally dependent, and warm, wet weather at flowering is most conducive to serious disease development

Fire blight is a bacterial disease, caused by the bacterial pathogen Erwinia amylovora, which exhibits symptoms on leaves, canes, flowers and fruit of raspberries and blackberries. Although this is the same organism that causes fire blight on pear and apple, it is a different strain. Thus the strain that attacks raspberries and blackberries will not infect apple or pear and vice versa.
The bacteria are likely spread from plant to plant by insects, wind, and splashing water. Rain, high humidity, and warm temperatures favor disease development. It is not known how and where the bacteria overwinter, although they likely survive in cankers on infected canes.
The most obvious and striking symptom are blackened cane tips, which bend over and die, resulting in a shepherd’s crook appearance. Infections may proceed down the cane for up to 25 cm and may produce cream-colored bacterial ooze under high moisture conditions. As the disease progresses down the cane, the veins of leaf veins and portions of the leaf surrounding the midvein turn black. Entire leaves may wither and die. Typically, discoloration and dieback is limited to succulent young growth. In addition, the disease can affect fruit clusters. Infected peduncles (the stalks of fruit clusters) turn black and the young developing berries become brown, dry and very hard. Entire fruit clusters may be infected, but generally a few berries in each cluster remain healthy.
No specific control measures have been developed because of the sporadic nature of the disease. However, the following practices will limit establishment and spread of the disease:
  1. Purchase and plant only disease-free plants from reliable stores;
  2. Remove and destroy diseased canes from the bushes as soon as possible;
  3. Manage insect pests to avoid a possible means of moving the bacteria from plant to plant;
  4. Avoid over-fertilization;
  5. Orient rows, prune and thin plants to maximize air circulation;
  6. Destroy wild or abandoned brambles growing nearby;
  7. Apply copper sulfate as a protective material, starting before or as soon as the first symptoms appear.
Fire blight often confused with Grey Mould. Both diseases can cause dry, hard, mummified fruit. In the case of fire blight, previously healthy leaf and cane tissue may be affected as well. Initially, fire blight infections exude an amber or milky ooze in humid conditions. It is important to identify fire blight infections soon after they occur because symptoms are indistinguishable from old botrytis infections later in the season.