Plant Pathology Infobytes

April 25, 1997
Fire Blight Is A Hot Disease This Spring

The appearance of dead terminal branches in many apple and pear trees this spring is an indication that fire blight, a bacterial disease, is active in many home orchards across the state. Increased fire blight occurrence can be attributed to recent periods of wet, cool weather favorable for fire blight development.

Fire blight is also causing twig and branch dieback problems in Bradford pear, a popular landscape plant. Additionally, flowering crabapples, pyracantha, cotoneaster, flowering quince, and other plants are susceptible, but have not been damaged as extensively by fire blight as Bradford pear.

Fire blight is a descriptive name for the problem, since disease symptoms include black, scorched appearing branches, twigs, and foliage. The most common symptom of fire blight is a shoot blight, which occurs when the entire end of the branch is killed by the disease.

To reduce the incidence and severity of fire blight, a full season program of disease management practices such as variety selection, pruning, proper fertilization practices, and chemical control have to be followed.

At this point in the season, control measures which may be used to control fire blight in orchards and landscape plantings are limited.

However, fire blight spread within trees can be reduced by applications of "fire blight spray," available at most garden supply stores under several trade names. Look for products which contain streptomycin sulfate as the active ingredient. This information is located on the product label.

Generally, one level tablespoon of this material should be mixed with two and one-half gallons of water and sprayed onto foliage and all branches of fire blight affected trees. To obtain best disease control with fire blight spray, the first applications should have been made at the start of the bloom period, and every five to seven days thereafter. For additional information on use of fire blight spray material, refer to product labels.

Additionally, pruning should be carried out to remove cankers and ends of blighted branches. In heavily damaged trees, delay the removal of infected shoots until early summer, or preferably until the dormant season to avoid spreading infection to healthy shoots.

If trees are lightly infected, spring or early summer pruning to remove newly infected twigs and shoots can reduce spread of the disease. New infections must be promptly removed as soon as symptoms are observed.

The recommended way of pruning is to remove diseased shoots ten to twelve inches beyond the last evidence of disease. To avoid spreading the bacterium, the pruning shears should be sterilized by dipping after each cut. Household bleach, diluted one to nine, is an acceptable sterilizing agent.

For additional information on a full-season fire blight control program, check with the County Extension Office.


Written by the late Dr. Frank Killebrew

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