Fireblight is a very damaging disease to pyrus and malus species of trees. In our area these trees include pear and flowering pear, apple and crabapple. Fireblight may also affect toyon, hawthorn or cottoneaster. Fireblight spreads during rainy periods and enters tree tissues through blossoms. The blossoms will turn black and wilt. The pathogen then moves into twigs and branches which develop cankers. These cankers may ooze and can be identified by dark streaks on the branches. The foliage wilts and browns giving the tree a burned appearance which the name fireblight is derived from.
Often fireblight can move through a group of street trees in an area causing large areas of dieback in the canopies.
Control of Fireblight
Fireblight spreads during warm, moist, or rainy periods and can also be spread by honeybees as they move from blossom to blossom. Pruning out affected branches is important in reducing the spread of the disease. Branches should be pruned during a dry period, preferably during the dormant season. Branches should be pruned 12 to 18 inches below evidence of the pathogen. Pruning tools should be sterilized with a 10% solution of bleach or a household cleaner like Lysol. Spray treatments are also a preventative measure that can be applied before the onset of symptoms. It may be advisable to spray trees that are susceptible cultivars or trees in area where fireblight outbreaks have occurred. Trees may be sprayed with a copper fungicide but several applications may be necessary during periods of high humidity. Copper fungicides may also affect fruit quality in fruiting pear and apple varieties.
It is important to monitor trees during blossoming to identify the disease and take prompt action if symptoms occur.
Another method of reducing the likelihood of fireblight is to plant varieties of trees that are resistant to the pathogen. Unfortunately, most pear and asian pear varieties are very susceptible. For ornamental flowering pears Red Spire and Capitol are more resistant to the pathogen than Aristocrat.