Fireblight

 

Fireblight symptoms usually occur in the spring, right after a rain or even a fog drizzle. Fireblight is a disease caused by a bacterium. The bacterium, Erwinia amylovora, survives from year-to-year in the tree. It becomes active in the spring when new foliage and blossoms are developing. The bacterium invades the flowers through the fruit and rapidly kills the flowers and often the associated twig. Death occurs in 24-48 hours, and the flowers, leaves, and twig turn dark brown to black (charred look). Thus the name “fireblight.” Fortunately for Central Coast gardeners, this disease is usually not severe. In northern California entire trees can be severely damaged with large branches being killed. If twigs are diseased, they should be pruned out as soon as they are observed. The pruning cut should be made 4-6 inches below the lowest visible diseased tissue as research has shown that the bacterium can invade the tree several inches beyond where symptoms appear. If the blackened tissues are few and slight, it is best to wait until the weather dries and warms up (summer time). In summer the bacterium becomes inactive and dies out in all but the diseased (killed) tissues. When pruning is done later in the year, only the immediate dead twigs and shoots need to be removed. If summer pruning is done several years in succession, most of the fireblight can be eliminated from the tree.