One of the most devastating diseases of fruit trees and which is difficult to control is a disease called fire blight. The bacterium — Erwinia amylovora — attacks many fruit trees including apple, pear and other rosaceous ornamental plants.
This list includes crabapple, pyracantha, cotoneaster, hawthorn photinia, quince, mountain ash, loquat and spirea. When disease conditions are right for disease development, it can rapidly kill the entire plant.
Fire blight begins in early spring when temperatures rise above 60 degrees Fahrenheit and the weather is rainy or humid. The infection starts with the flowers, which turn black and die. It then moves down the branch, which kills the branch.
The branches may blacken and curl over giving the appearance of a “shepherd’s crook.” What you usually spot first are the dead leaves on the branch, which look like they were hit with a blow torch, hence the name fire blight. It can affect the blossoms, stems, leaves and fruit.
The disease spreads from overwintering bacteria in the bark. Wet spring weather begins the onset of a milky-like, sticky liquid that oozes from infected plant parts. Insects spread the bacterium to the flower and pollinators spread it from flower to flower.
Rain washes it into the flower itself which then infects the branch. Plants heavily fertilized with nitrogen are more susceptible because the bacterium flourishes on new growth. It can also move systemically within the plant. Peeling the bark back may reveal red-streaked wood underneath rather than healthy tissue.
Prevention and treatment are the only options. There is no cure for fire blight. One of the best controls is plant resistant varieties. Pruning infected plant parts reduces the spread of fire blight.
Cuts should be made at least 8 to 12 inches below the infected tissue. Skin back the bark to the point where the tissue is healthy to be sure.
Remove all the suckers from the base of the tree. They are more susceptible to fire blight. Disinfect between cuts by using a one part bleach to nine parts water solution or 79 percent alcohol solution. You don’t want to spread the infection at the new cut.
Applying bactericides containing streptomycin and a copper fungicide at the beginning of bloom for apples and pears is recommended. Follow all label directions. Never apply insecticides at bloom because it will kill pollinators.
Controlling insect pests is also important in stopping the spread of fire blight. If the trees are large, it becomes very difficult to get adequate coverage of the foliage.
Fire blight can be very damaging to fruit trees but if you can catch it early you may save the tree. Preventive care is the best method.
What’s going on in Extension?
Saturday, April 30 — MGEV Plant Sale, 9 a.m.–2 p.m. at the Ag Center. They will have a wide variety of plants for sale. Come and see!
Thursday, May 5 — Timber Growers; guest speaker: Ben Jackson, “Soil Mapping.”
Friday, May 13 — Egg Candling Class for all those who sell eggs in Georgia. 10 a.m.–3 p.m. at the Ag Center. No cost. Must pre-register! Only 50 slots available.
Brian Maddy is the ANR Agent for Troup County Extension. The Troup County Extension office is located at 114 Church St. in LaGrange and may be reached at 706-883-1675, Monday–Friday 8 a.m.–noon and 1–5 p.m.