Fire Blight Treatment & Prevention for Bay Area Pear, Apple & Ornamental Trees

The earliest sign of fire blight is blossom blast—flowers wilt, turn water-soaked, and turn dark brown or black. As the infection travels down succulent green shoots, terminal twigs curl sharply at a 180-degree angle, resembling a shepherd's crook. Leaves scorch black or dark brown but remain firmly attached to dead branches, giving the tree the appearance of having been singed with a blowtorch. In warm humid weather, milky-orange bacterial ooze seeps from infected bark, attracting pollinators that inadvertently spread the pathogen.

Chemical sprays cannot cure established wood infections; pruning is the primary control. However, improper pruning will spread fire blight throughout your canopy. Pruning must be executed during dry summer weather or winter dormancy. Cuts must be made at least 12 to 18 inches below the lowest visible discoloration or sunken bark canker. Between every single cut, shears and saws must be thoroughly disinfected using a 10% household bleach solution or 70% isopropyl alcohol.

Preventing infection begins during the spring bloom window. Certified arborists apply fixed copper bactericides or biological inoculants (such as Bacillus subtilis) as flowers first open to prevent bacteria from colonizing the pistils. Furthermore, avoid high-nitrogen fertilizers that stimulate tender, succulent shoot growth, which is exceptionally vulnerable to bacterial invasion. Switch to low-nitrogen deep root feeding to promote root resilience.

If fire blight penetrates the main trunk scaffold or rootstock, the tree cannot compartmentalize the infection. The bacteria girdle the vascular cambium, cutting off water transport and causing rapid canopy death. In advanced trunk infections, our arborists recommend swift tree removal to eliminate the reservoir of bacterial inoculum and protect surrounding neighborhood fruit trees.