Fire blight widespread in Gunbarrel and Niwot

Have you looked up into your apple tree this year and noticed some of the leaves and branches are brown and withered, almost as if they’ve curled up and died?

Chances are, it’s fire blight.

Fire blight is an endemic disease caused by the bacteria Erwina amylovora, and right now it’s having a banner year in Gunbarrel and surrounding areas. Typically affecting fruit trees such as apple, crabapple and pear, fire blight can also infect quince, mountain ash, hawthorn and serviceberry trees.

While fire blight rears its head every year, conditions this year have been particularly friendly to this fatal tree disease. The warm, wet spring weather coupled with all those hail storms helped boost the infection rate in the area. According to Josh Morin, co-owner and Master Arborist at Taddiken Tree Company, many arborists refer to the Front Range as “Fire Blight Alley,” because our volatile spring weather often provides favorable conditions for the spread of infection.

Once a tree has been infected, there is no cure, only management of the disease. How does a tree become infected? Bacteria are spread in the spring, after overwintering on cankers on the tree. As the weather warms, the bacteria reproduce rapidly and are then forced out of the tree cracks and bark pores in a sweet and gummy bacterial ooze.

Insects, pollinators, rain, hail and contaminated pruning tools all contribute to the bacteria’s spread, which can get in through wounds in the bark or branches, blossoms, and leaves. It can even be spread by composted leaves and branches, so make sure to always burn or trash any infected materials once they’ve been removed from the tree.

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While there is no cure, fire blight does take several years to kill the tree. With proper care and management, most trees can survive and thrive. Right now, pruning is ill-advised, because it is too easy to spread the disease in spring and summer without proper tool sterilization.

Instead, focus on the tree’s health this summer by making sure it gets adequate water. Morin advises irrigating your trees with 10 gallons of water per one inch diameter of the tree trunk. Leaving a trickling hose at the base of a tree for two hours two times per week would fit the bill nicely, and will keep your trees less stressed while they work their way through our typically dry summer.

Be wary of treating the tree with a high-nitrogen fertilizer as this causes the disease to spread more rapidly. Instead, consult with a Certified Arborist about winter pruning practices to help best manage the disease so that your trees can start next spring in the healthiest possible way.

Also, consider planting disease resistant varieties of your trees that are currently infected. The Colorado State University Extension has a list of fruit and ornamental trees that are resistant to this pervasive disease at http://www.extension.colostate.edu.

Watch for follow-up articles this fall to learn more about how you can help your trees survive.