Fire blight takes toll
on pears, apples
By Staff
Steve Strong
May 14, 2003
Fire blight is a deadly bacterial infection that attacks more than 75 of different host plants, including apple, crabapple, pear, rose, pyracantha, hawthorn and spirea.
Bradford pear is one of the most popular choices in modern landscapes, and is among the many prized ornamentals falling victim to this fatal dieback.
The first symptoms appear during the flower cycle, as bees and other insects visit the blooms to collect pollen and nectar.
The insects travel from infected plants to others in the orchard and landscape, transmitting the bacterial infection to new flowers, leaves and stems.
Old stems ooze bacterial juice as the spring sap begins to flow, attracting aphids, leafhoppers and other piercing insects to hasten the disease spread.
Once the bacterial ooze makes it outside the stem, rain showers rapidly carry the pathogen from branch to branch, leaving scorched-looking tips that resemble a shriveled "shepherd's crook."
Severely infected trees may look as if they have actually been scorched or burned by fire, hence the common name for the disease.
The brown or blackened branch tips serve as infection sites for following growing season, so removal of diseased tissue is important to prevent further disease spread.
Fire blight, like most bacterial diseases, is very hard to control. Pruning infected branches is one of the few ways to manage the problem, and it is best done in early spring or fall when trees are not actively growing.
Pruning during the growing season (now) requires some extra precautions.
First, mix a disinfectant solution of 10 percent bleach (nine parts water to one part bleach), and be sure to dip pruning shears before making each cut.
Next, make all pruning cuts at least 6 inches below any sign of visible infection.
Bacterial and fungal infections tend to be worse on new, succulent growth. Excessive use of nitrogen fertilizers promotes rapid plant growth that is more prone to disease attack, so go easy on the plant food early in the growing season.
Blossom sprays can be effective in preventing fire blight infections if used at the right time during the flowering cycle.
Streptomycin antibiotic is available at local farm suppliers, and should be applied at 5 percent, 50 percent, and again at full bloom.
Disease resistant varieties are another option for homeowners, but none of the known host plants are completely immune to fire blight attack.
The Mississippi State University Extension Service maintains plant lists for disease resistant fruit and ornamental varieties, and can be found online at www.msucares.com.
For more local information, call the area horticulture agent at 482-9764.
Each county Extension office offers free publications on vegetable, fruit, and ornamental plant culture.
Stop by for a visit anytime from 8 a.m. to 5 p.m. Monday through Friday.
