Fire Blight a Concern


One of the most frequent horticulture questions asked is “What is wrong with my apple tree?” This was a year with the right environmental conditions to produce the bacterium Erwinia amylovora that causes the fireblight disease. The disease is characterized by sudden wilting, followed by shriveling and blackening of the blossoms, young shoots and developing fruit. The foliage looks like it as been scorched by fire, hence the name fireblight. Fireblight attacks both fruit and ornamental plants of the rose family. These plants may include apples, pears, mountain ash and cotoneaster.

Outbreaks of fireblight tend to occur in warm humid weather.  Even though the disease is very sporadic and may not appear again for many years, precautions should still be taken to decrease the chance of infection in the following years. Prune and burn diseased twigs while the tree is in dormancy if the infection is light.  If there is a heavy infection with more humid wet weather on the way, then prune in the summer. This decreases the chances of spreading the bacterium. If you choose to prune this fall or winter when the plant is dormant, don’t worry about forgetting which areas of the tree were infected, because the dried leaves and fruits tend to remain on the tree through the winter. Cut at least 10-15 inches below the edge of the infected area or canker. After each cut, sterilize the cutting tools and the cut surface with a disinfectant to avoid further spreading. 

Two possible disinfecting solutions are:

1. Bleach diluted to 20 percent (3 cups to 1 gallon water) plus Regular Lysol containing o-phenyl-phenol and o-benzyl-p-chlorophenol, diluted to 20 percent. This should smell like creosote and is highly effective.

2. Denatured ethyl alcohol (available as shellac thinner) plus Pine Sol (19.9% pine oil). This is almost as effective as the bleach Lysol solution.

Dip shears, knife or saw in the disinfectant or pour over the cutting edge. Bleach and Pine Sol are very corrosive to tools, so rinse and oil them after using these solutions. 

To help prevent infections next spring, the antibiotic streptomycin can be used during flowering. Read and follow the label instructions for application.

Another preventative approach for controlling fireblight is to plant resistant varieties. These varieties will also be susceptible to the disease but will be less so than non-resistant varieties.

For more information about fireblight, call the Roosevelt County Extension office at (406)787-5312



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