Tree with fire blight. Image courtesy of Salida Tree Board
Do Not Prune Now
Are your fruit trees exhibiting worrisome conditions such as dead branches, light brown to blackened leaves, discolored bark, “shepherd’s hook” twigs, and dried fruit? These conditions could be an indication of fire blight, a bacterial disease that affects certain species in the rose family (Rosacea).
According to Colorado State University Extension, this disease can be especially destructive to apples, pears, and crabapples. It can also occur on serviceberries, flowering quinces, cottoneasters, hawthorns, quinces, pyracanthus, blackberries, raspberries, and mountain ashes.
Rainy springs, such as Chaffee County experienced this year, are conducive to rapid spread of the pathogen. Thankfully, hot summer weather that we are now experiencing generally slows or stops the disease.
Fire blight bacteria can be spread by insects, splashing rain or contaminated pruning tools. There is no cure for this disease, therefore prevention is the best management solution. Planting resistant varieties is most effective, although no cultivar is immune to infection when the pathogen is abundant and conditions are favorable for infection.
Chemical sprays such as copper or streptomycin are preventative treatments that must be applied prior to the onset of symptoms to be effective. Application timing is imperative and use of the Midwest Tree Fruit Spray Guide at https://extension.entm.purdue.edu/publications/PM1282-1.pdf is recommended.
Pruning all blighted twigs and cankered branches 8 to 12 inches below the edge of visible infection is effective against the progression of the disease. CAUTION! Pruning should only be done in mid-winter in order to lessen the spread of the bacteria. DO NOT PRUNE NOW as this will open additional wounds for the bacteria to infect!
Unless pruning in mid-winter when bacteria are dormant, be certain to surface STERILIZE all tools AFTER EACH CUT with either household bleach, ethyl alcohol, or household spray disinfectants. Treat all pruning wounds with a 70 percent alcohol solution. Promptly remove and destroy all removed infected plant material.
For more information on fire blight and treatment, visit https://extension.colostate.edu and search for Fact Sheet 2.907-1. Or contact the Chaffee County Colorado State University Extension office at 719-539-6447.
By Kris Cheskaty
Salida Tree Board
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