Fire Blight Occurring On Pear Trees

A bacterial disease called Fire Blight showing up on pear and apple trees. Fire Blight actually infects the tree during the bloom stage in early spring. The disease itself overwinters in cankers and starts growing in the spring. The bacteria will ooze from disease cankers and then is spread to blossoms or twigs by insects. Bees actually spread the bacteria from bloom to bloom and from tree to tree during the spring of the year.

On pear trees, the young twigs and branches die from the terminal end and appear to turn black as if they were burnt by a torch. The end of the affected branch may bend and resemble a shepherd’s crook.

On apple trees, the same symptoms occur except that the dying branch tips will turn a deep reddish brown color instead of a black color.

Not only will this disease show up on the terminal growth, but if it is allowed to remain on the tree, it can spread to the twigs and even later on to the fruit itself.

On the twigs, a canker often forms that girdles the twig at the base of an infected fruit spur. The infected twig will grow in a hooked form and may have a shiny or oily appearance in the summer. Milky or brown material may be seen oozing from the twig in hot, humid weather.

On the fruit, Fire Blight will first show up as a water-soaked area and later will produce an ooze. The fruit eventually turns brown, shrivels up, mummifies, and then turns black.

Fire Blight occurs more prevalently when we have moist conditions in the spring at the time our pear and apple trees are blooming. It requires a favorable environment when temperatures are between 65 and 80 degrees Fahrenheit and high humidity conditions are occurring.

Some pear tree varieties are more resistant to Fire Blight than others. Fruiting pear varieties that show good resistance to Fire Blight include Orient, Carrick, Waite, and Warren.
Ornamental pear varieties such as Bradford are also moderately resistant to Fire Blight but it can occur on them during favorable weather conditions in the spring. Bradford pears do not get typical Fire Blight symptoms. Infected Bradford Pear tree leaves turn a rust color and appear scorched and spotted. Portions of the leaf remain green.

Preventative sprays applying a material called streptomycin sulfate can be made in early spring at the time the trees begin to bloom to prevent infection. Streptomycin sulfate must be applied beginning at the time the tree has about 10% of the blooms open and sprays must be made at 5 day intervals (every two to three days during wet conditions) throughout the bloom stage until the blooms begin to shed off.

The best measure that you can take to prevent this problem from reoccurring on your pear and apple trees again next spring is to prune out the infected growth and get these infected branches away from your trees. Prune out affected branches at least 6 inches below the sign of infection. Dip your pruning shears in 70% isopropyl alcohol (rubbing alcohol) or a 1 part bleach to 9 parts water solution to disinfect your pruning shears between each cut.

Avoid heavy nitrogen fertilization during the mid to late summer period around your pear and apple trees. Highly fertilized trees that are producing a lot of new growth late in the summer seem to be more susceptible to Fire Blight the following spring.