How to Treat Fire Blight? | Management That Works

Fire blight has no cure, but prompt pruning, tool sanitation, and preventive sprays timed to bloom can manage the disease in apple and pear trees.

For the full breakdown, see our best Fire Blight Spray guide.

Fire blight moves fast. A shoot can wilt, blacken, and curl into a shepherd’s crook in days, and once the bacteria are inside the tissue no spray can reverse the damage. Here is how each piece works.

Prune Infected Tissue Correctly

The only way to remove fire blight from a living tree is to cut it out. Do not wait for dormant pruning — remove infected shoots and branches as soon as you spot them, as long as the weather is dry. University of Tennessee Extension warns that pruning during wet conditions spreads the bacteria.

Cut well below visible symptoms. UT Extension recommends going 10–12 inches into healthy wood; Cornell says 8–12 inches below the last sign of disease. A shallow cut that leaves infected tissue behind lets the bacteria keep spreading. For infections in older wood, use the “ugly stub” method described in Penn State’s 2025 update: leave a 6–8 inch stub, then remove it during dormant pruning. For trunk or rootstock cankers, Cornell advises removing the entire tree — these infections cannot be cut out cleanly.

You will know the cut was deep enough when you see clean, white wood with no brown streaking beneath the bark.

Sanitize Tools and Destroy Debris

Fire blight spreads on pruning shears and saw blades. Cornell recommends sterilizing tools with a 10% bleach solution between every cut, then oiling them afterward to prevent corrosion. Skip the sanitizing step and you risk infecting every branch you touch next.

Remove every piece of pruned material from the area. Cornell says to burn infected prunings or let them dry completely and then flail mow. Never leave infected branches on the ground near healthy trees, and avoid dragging pruned material through the orchard as you work.

Apply Preventive Sprays at the Right Time

Sprays do not cure fire blight — they prevent it. UT Extension gives a rate of 100 ppm (8 oz per 100 gallons or about 1 teaspoon per gallon), starting when 20% of blooms are open and continuing until petal fall. Repeat every 5 days under normal weather or every 3–4 days during warm conditions.

Copper products are another option for reducing bacteria on tree surfaces. Cornell says copper can be applied from late dormant through green tip, but after pink stage it may cause fruit russetting. For dormant trees, UT Extension recommends Bordeaux mixture (8 lbs copper sulfate, 8 lbs spray lime, and 1 gal dormant oil in 100 gal water), applied before the silver tip stage.

In Penn State’s 2025 protocol, after pruning out fire blight you can apply Actigard at 1 oz per quart of 1% penetrant to the cut and 1 meter of trunk below the infected limb. Another option is prohexadione calcium (Apogee or Kudos at 12 oz/A), with a water conditioner because calcium can interfere with the spray.

Cornell warns against overusing antibiotics: limit bloom applications to three or fewer, alternate materials, and avoid summer use against shoot blight to slow resistance.