By Eddie Ayers, County Extension Agent
I have been getting a lot of calls and samples brought into the office of trees that are dying at the tips. Most of these are related to apples and pears. The cause of this death is a disease called Fireblight. The disease affects plants in the Rosaceae family. The plants affected include Amelanchier (serviceberry), Chaenomeles (flowering quince), Cotoneaster (cotoneaster), Crataegus (hawthorn), Eriobotrya (loquat), Malus (apple and crabapple), Photinia (photinia), Prunus (flowering almond, plum and cherry), Pyracantha (pyracantha), Pyrus (pear), Rosa (rose), and Spirea (spirea).
Fireblight is a destructive, highly infectious and widespread disease caused by the bacterium Erwinia amylovora. Fire blight attacks blossoms, leaves, shoots, branches, fruits, and roots. The most infectious time is when three conditions are present: moisture, warm temperature, and an open bloom or wound.
The bark at the base of blighted twigs becomes water soaked, then dark, sunken and dry; cracks may develop at the edge of the sunken area. Young twigs and branches die from the terminal end and appear burned or deep rust colored. Branches may be bent, resembling what is commonly referred to as a “shepherd’s crook”. Dead leaves and fruit remain on the branches.
Once established in the tree, Fireblight quickly invades through the current season’s growth into older growth. Fireblight can be spread from diseased to healthy plants by rain, wind, and pruning tools. The bacterium can survive the winter in sunken cankers on infected branches. In spring, the bacteria ooze out of the cankers and attract bees and other insects. Insects also help spread the disease to healthy plants.
During spring and summer, prune out infected branches 8 inches below the damage. Avoid pruning when the plants are wet. Dip pruning tools in 70 percent isopropyl alcohol (rubbing alcohol) or 10 percent bleach solution (1 part bleach to 9 parts water solution) between each cut. Wash and oil shears when you are finished. These practices avoid spreading the pathogen. Also avoid splashing water and heavy nitrogen fertilization, especially in summer, when succulent growth is most susceptible to Fireblight infection.
Chemical control is not always effective and needs to be applied preventively. Therefore, in years when warm, humid, wet weather coincides with flowering and leaf emergence, spray plants with a fungicide containing basic copper hydroxide (Kocide) or Captan or sulfur, or an antibiotic, streptomycin, to reduce infection. Applications of streptomycin need to begin at the start of blooming and continue every 3-4 days during the bloom period when moisture and the warm temperatures are present.
For more information about Fireblight, contact me in the Gilmer County UGA Extension office.