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Fire Blight

Fire Blight – the fire danger you didn’t know about

Fire blight effects pear and apple trees and the cause has nothing to do with fire. The infection is actually caused by a bacteria which results in a tree looking like sections of it have damaged as if caused by fire.

The bacterium is called Erwinia amylovora and it forms colonies in the flowers. This bacteria rapidly divides when temperatures hit above 70 degrees F. Then if a rain occurs the bacteria can be washed down into the floral nectary which can successfully infect the developing fruitlet. If this occurs the disease can spread in between the bark and the wood of the tree, otherwise known as the cambium.

Once the infection has spread the only solution is aggressive pruning and to destroy all limbs that have been pruned off of the tree.

Signs of fire blight are tips of shoots wilt rapidly and form a “shepherd’s crook.” Leaves will turn brown and sometimes even black and they stay attached to the limb. Cankers will appear on the tree, often appearing black and dry.

There are several factors that contribute to a tree’s infection. Younger trees are more susceptible. Older trees, past the age of three, can be effected but are much less likely to die from the infection. Some rootstock is highly susceptible to blight as is some various cultivars. Tree vigor has some influence based on the age of the tree, nutritional status, and crop load of the tree. The weather can help predict a bad season of fire blight. You can go to www.decisionalaid.system for a predictive model of fire blight breakouts. The model will be turned back on August 20th.

To control fire blight trim out old blight cankers. Make sure to remove cuts from orchard and destroy. If pruned limbs are left in orchard they can continue to spread the blight through cross-pollination contamination. When you see blight during the summer remove immediately. Planting blight resistant rootstock is another option. Watch the model and apply preventative sprays when prediction of fire blight is high. For biological and chemical methods of fire blight suppression visit treefruit.wsu.edu/fire-blight for more information.

If you think you might have a case of fire blight or another issue with one of your garden or houseplants bring it to the Master Gardener Plant Clinic. The clinic is every Tuesday all summer long from 2:30-4:30 pm at the WSU Extension office, 986 S. Main, Colville WA. Here a Master Gardener can look at your plant sample, do some research for you and attempt to help you resolve your gardening issues. If you have any further questions you can e-mail us at extensionstevens@wsu.edu or call the office at 509-684-2588.

Further references:

Fire-Blight: Everything you want to know

Apple Fire blight Factsheet

Cherry fire blight  

Fire Blight Model : Has been turned off from June 21- August 20

Fire blight example on apple tree. Courtesy Adena Sabins MGPC
Fire blight example on apple tree. Courtesy Adena Sabins MGPC
Fire blight example, gala apple tree. Courtesy Adena Sabins MGPC
Fire blight example, gala apple tree. Courtesy Adena Sabins MGPC
Fire blight onlimb of gala apple tree. Courtesy Adena Sabins MGPC
Fire blight onlimb of gala apple tree. Courtesy Adena Sabins MGPC
Fire blighted fruit. Photo courtesy Adena Sabins MGPC
Fire blighted fruit. Photo courtesy Adena Sabins MGPC
Fire blight on limb of gala apple tree. Photo courtesy Adena Sabins MGPC
Fire blight on limb of a Gala apple tree. Photo courtesy Adena Sabins MGPC