September 20, 2017 - Scott's Exterior Maintenance
We've had some questions regarding issues showing up with ornamental pear trees, so I thought it was time to do a post on fireblight.
During the past few years we've seen widespread fireblight infections showing up all over the area. Although it can affect many trees and shrubs in the rose family, including apples, crabapples, edible pears, and ornamental pears, we're especially seeing the prevalence on the ornamental pears since it's a very common landscape and street tree. These would include Aristocrat, Autumn Blaze, Redspire, and Bradford pears, if any of those names sound familiar.
Here are some basics about Fireblight:
- Fireblight is a bacterial infection.
- The bacteria over winter in cankers on infected trees.
- In the spring, it becomes active and the cankers start to ooze.
- Insects track the bacteria from an infected tree to a potential new host. It's also spread by wind and rain.
- When the bacteria lands on a susceptible tree, a new infection can begin.
- The period of highest susceptibility is during spring and the bacteria most likely enter the tree through its open flowers, its succulent new growth, or wounds in the bark.
- Due to the nature of bacteria, infection is worse during periods of high moisture, high humidity, and warm temperatures.
- Once a tree has been infected, depending on a number of factors, it may progress somewhat slowly or very rapidly. May only kill the branch tip or may kill the whole tree within a few months.
- Due to the fact it infects the flowers and new growth, it starts at the branch tips and then progresses down the branch, killing the leaves and branch as it goes.
- Although infection happens in spring, we may not notice it until July as the heat of summer makes the bacteria progress faster and also makes the dead leaves show up more clearly.
- Cankers develop and the bacteria overwinter. The cycle starts over again in the spring.
We get a lot of questions regarding what can be done with susceptible and/or infected trees. There are so many variables, it really needs to be looked at on a case by case basis.
- There are sprays available, but timing is tricky and it has to be done in spring during the period of highest susceptibility when infection is likely to occur. The goal here is catching the infection before it starts.
- After infection, depending on severity, pruning out infected branches can be effective. This is most effective on varieties that are somewhat resistant on their own and only show scattered infected branches.
- Older trees that are infected, varieties that are naturally highly susceptible, trees that show significant infection and dieback, trees with visible oozing cankers, and trees with infection in the main stems and trunks are best removed and destroyed.
Anyone planting new ornamental pears should look for and specifically ask for varieties that are fireblight resistant. Or consider planting something else.