By Nancy Borkholder
Ag/NR Secretary
Fireblight is a bacterial disease that affects apples, pears, crabapples, ornamental pears and about 70 other plants in the Rose (Rosacease) family. It is a disease that is most severe in warm, wet weather, describing our 2015 spring to a T.
Fireblight overwinters on cankers on infected plants, where it will begin to ooze spores in the spring. The spores can be spread by wind, rain, insects and birds, as well as mechanically when people cut out infected branches. This disease can be very severe, resulting in crop losses, loss of major limbs or even death.
Reliable control methods for fireblight are really not available at this time, so we have to rely on prevention on the disease. Preventative measures include selecting varieties that are resistant, selecting good planting sites to reduce plant stress, conservative fertilization practices which minimize succulent growth and proper pruning practices. Pruning in the late winter or very early spring can help minimize risk of infection.
For trees that are found to be infected, avoid pruning the tree when you are attempting to manage the disease with fungicides. Pruning should be done in dry weather, with cuts made at least 12 inches below the site of infection. Delay summer pruning until the terminal bud is set, and growth has stopped for the summer.
Good sanitation is also important. Dispose of all infected materials and sterilize pruning equipment between cuts by dipping in a solution of 10 percent bleach plus some detergent. If a tree canopy is more than 50 percent infected, it is best to remove the tree.
Chemical management is generally not recommended after petal fall, so we are well past the prime time to control the disease. Next season, before the buds break open, copper based fungicides or other fungicides can be applied. Streptomycin, an antibiotic, is also labeled for control before petal fall. It is very important to avoid using the streptomycin products after the signs of the disease are present. This will not cure the problem, and can only hasten disease resistance to the streptomycin.
For more information, check out Purdue Extension’s Fireblight in Fruit Trees publication, written by Janna Beckerman, a Purdue Plant Pathologist. https://www.extension.purdue.edu/extmedia/BP/BP-30-W.pdf
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