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Written by Linda Langelo   

Fire blight

Carefully review the list of plants below:

Apple, pear, crabapple, serviceberries, flowering quinces, cotoneasters, hawthorns, pyracanthas, blackberries, raspberries and mountain ash.

All these plants are members in the rose family and each share the disease called fire blight. In springs like this year that are wet and warm, this bacterial disease is highly conducive to spread rapidly.

What should you be looking for as symptoms of the disease? Here are several things to look for when examining these plants: 1) dead branches, 2) water-soaked blossoms, 3) light-brown to blackened leaves, 4) discolored bark, black “shepherd’s” crook twigs and 5) dried fruits.

Once the disease begins and goes unnoticed, the bacteria overwinters on the branches as cankers, and in spring, those cankers ooze a sweet, gummy exudate called bacterial ooze. The next issue will be insects that are attracted to the ooze and then get it on their bodies and carry the disease farther. Among these insects are ants, bees, beetles, flies and aphids.

The best practice in stopping or slowing this disease is to purchase more resistant cultivars of the plants listed above. Although no plant or cultivar of the plants listed above are immune to this disease, the key to keeping the plant in the best health possible is by selecting varieties that are best suited to our local area.

Colorado State University’s fact sheet on fire blight No. 2.907 provides a list of apple and pear tree cultivars ranked by their susceptibility to fire blight.

As an example of apple trees, Golden Delicious is highly susceptible, Haralson is moderately susceptible, and Honeygold is moderately resistant. You can access the fact sheet by going to CSU Extension’s website and clicking on fact sheets and publications. Or visit your local Extension office to pick up a copy.

In controlling this disease, I would take a proactive plan. Symptoms first appear at petal fall. I would look for water-soaked and wilting petals that will next turn brown.

Even before seeing these symptoms, if the weather is conducive to fire blight, I would limit the amount of nitrogen fertilizer and major pruning cuts. Both will reduce succulent tissue growth, which is the most susceptible to fire blight. I would also review our CSU fact sheet for other preventative controls applicable for your situation and plant.


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Holyoke Enterprise July 31, 2014