Friday, May 29, 2015

Fire Blight in Pear Trees

Fire blight is a serious disease in fruit trees and other ornamental plants.  The photo above shows one of my pear trees (in the front) infected with Erwinia amylovora, the bacteria that causes fire blight disease. You can recognize fire blight by the burned or blasted appearance of the tree's branches. The ends curl under too, like a shepherd's crook, and the fruit on the infected tree can be diseased, twisted, or weak.

Bacteria overwinter in infected trees, and when the sap begins to flow in the spring, the bacterial spores ooze out of the tree. Wind, rain, gardening tools and even beetles carry the spores from infected plants to healthy plants. Once a tree has the disease, there's little you can do to cure it, but a lot you can do to help the tree stay healthy on its own.

First, don't panic. Many trees can withstand some fire blight. The pear tree in my orchard shown here is seven years old, and it's probably had fire blight for five of those seven years. The pear tree behind it also had fire blight last year, but careful pruning seems to have removed most of the diseased limbs.

The Virginia Cooperative Extension office recommends the following treatment plan if you detect fire blight in your ornamental trees and shrubs:

  • Prune out the infected branches in the late summer or early fall.
  • Bury or burn the infected branches that your prune from the trees. This keeps the bacteria from spreading.
  • Sterilize pruning tools with alcohol or a bleach solution of 1 part bleach to 9 parts water. I sterilize tools before moving on to the next tree, but if I have a seriously infected tree, I might swab down the pruners with alcohol more frequently to prevent spreading the spores into healthy tissues on the same tree.
  • Don't use high nitrogen fertilizers. This causes as flush of new growth, which the spores love.
Unfortunately, chemical controls do not work well on fire blight, so your best defense is a good offense. Planting disease-resistant varieties is a smart idea. Purdue Cooperative Extension provides a good list of varieties resistant to the disease.

I did not know about fire blight when I planted my fruit trees years ago, but thankfully it seems to be contained to only one or two trees in my orchard. As you can see from the picture below, there's hope yet - baby pears are steadily growing on my trees.

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