How To Protect Orchards from Fire Blight

By Scout Nelson

Apple scab often receives the most attention in Minnesota orchards, but in years with mild winters and warm, wet springs, fire blight caused by the bacterium Erwinia amylovora can become a challenge. Although the disease is less persistent in Minnesota than in warmer U.S. regions, local growers still face risks when weather conditions favor infection.

Bacteria enter trees through wounds or blossoms, especially during bloom. Blossom blight is less common in Minnesota due to colder winters and cooler spring temperatures, which reduce bacterial survival. However, shoot infections, or “fire blight strikes,” are more frequent and can occasionally spread to a tree’s central leader. Hail, pruning wounds, and insect feeding can also increase infection risk.

Chemical tools play an important role in management. Copper-based sprays applied during dormancy help prevent early infections, while streptomycin formulations are effective against blossom blight but must be used carefully to avoid bacterial resistance. Certain bloom thinners, such as lime sulfur, can also reduce infection. For shoot infections, Apogee can slow vegetative growth, lowering disease risk, while Actigard stimulates natural defenses. Used together, they may offer strong protection.

Cultural management is equally important. Growers should prune infected shoots 12–16 inches below visible symptoms. Current research shows that sanitizing pruners is unnecessary if cuts are made far enough back. Removal of visible cankers after harvest and pruning out darkened wood also reduces next year’s inoculum.

Dr. Suzanne Slack of Iowa State University noted that U-Pick orchards should not worry about customers spreading fire blight once trees begin to harden off. She also advised avoiding streptomycin late in the season to reduce resistance risk. For severe infections, complete tree removal is rarely needed; cutting above the graft union can allow regrowth of the central leader.

While Minnesota winters often reduce fire blight pressure, changing weather patterns and events like hailstorms can increase risks. Consistent monitoring, careful chemical use, and cultural practices can help orchard managers protect trees and maintain long-term productivity.

Photo Credit:istock-rixipi