Bradford pear under fire from bacterial disease

By on July 13, 2016

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If you have a Bradford pear in your yard, you may have noticed it is adorned with dead leaves and brown and curled branch tips this year. The problem goes far beyond your own front yard though; across the state, Bradford pears look nothing like their normal state as an idyllic ornamental tree. While the symptoms may be obvious, the culprit itself is a microscopic bacteria that causes a disease called fire blight. This bacteria can infect many types of fruit and ornamental trees in the rose family, even killing species considered most susceptible.

Fire blight causes browning and curling of shoot tips on diseased trees. This year, the disease is widespread in Bradford pear. Image: S. Thompson, NCFS.

Fire blight causes browning and curling of shoot tips on diseased trees. This year, the disease is widespread in Bradford pear. Image: S. Thompson, NCFS.

The warm and wet conditions this spring provided the perfect environment for the fire blight bacteria’s growth, leading to widespread disease. Things started off fine with the trees blooming beautifully as always, but soon after, the flowers and young shoots began to turn black. What was not visible was the fire blight bacteria infecting new growth through infected rain splash or insect vectors such as cicadas or honey bees. After entering the tree through the flowers or small wounds, the bacteria spreads rapidly, killing plant tissues and causing shoot tips to bend over like a shepherd’s hook.  These dead, blackened leaves hang on the tree throughout the summer, giving it a scorched appearance, hence the name “fire blight”. Once the trunk of the tree is infected, it will carry the bacteria forever.

Bradford pear is considered less susceptible to fire blight than most pear varieties. The tree may become disfigured but typically will not die. New growth such as fruits, flowers and shoots are most vulnerable. To reduce disease, pruning, fertilization and irrigation should be avoided during the spring. Because the bacteria can spread from tree to tree on contaminated equipment, pruning tools should be sanitized with bleach or alcohol between pruning jobs.

If fire blight is known to occur in the area, there are bactericidal sprays that may help reduce new infections. These are applied to new blooms during the spring, but because applications are needed every three to four days and are challenging for larger trees, this option may be unreasonable or costly in most urban settings.

So, break out your pruning shears. Keep the tree trimmed regularly, a practice which will increase air circulation and reduce the conditions in which many diseases thrive. You’ll thank yourself later!

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