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Fireblight is a destructive and contagious bacterial infection which affects apple, pear, quince, and related trees. This infection can destroy an entire orchard in a single year if it is allowed to grow unchecked, and it can become a recurrent problem once trees have become infected. Several techniques can be used to reduce the risk of developing fireblight, and there are also tools which can be used to manage ongoing infections.
The disease is caused by infection with the Erwinia amylovora bacterium. The bacterium usually starts infecting the flowers, spreading down the branch. As the bacterium grows, the leaves and branches turn black, looking as though they have gone through a fire, and scabby lesions may appear. The bacterium also overwinters in the branches, appearing again in the spring and causing the infection to recur.
When fireblight manifests, the infected branches need to be removed by pruning well below the site of the infection. The branches should be burned, and the pruning shears should be wiped down to avoid spreading the bacterium to other trees. Trees with a history of infection can also be sprayed in the spring or winter to prevent the emergence of overwintering bacteria.
Several horticultural practices will discourage growth of the bacterium. Trees should not be pruned and fertilized in wet weather, as the wet weather and new growth will encourage overwintering bacteria to emerge. It is also important to avoid encouraging late season growth in the summer or fall, as this can create an opportunity for the bacteria to settle on the tree and last out the winter. All dead limbs destroyed by fireblight should be removed and properly disposed of in the fall.
Some cultivars are more resistant to fireblight than others. In an area with a history of this bacterial infection, it may be advisable to use resistant cultivars, rather than growing more vulnerable ones. Many nurseries are happy to order specific tree cultivars by request, or to make recommendations to people seeking blight-resistant trees. Gardeners can also look for orchards which appear to be doing well in an area with recurrent fireblight infections, and find out which cultivars are in these orchards.
Because fireblight is contagious, gardeners should keep an eye on neighboring trees and plants. If fireblight appears to be manifesting and the owner of the garden does not appear to be taking care of it, a neighboring gardener may want to offer assistance or tips.