Questions have been plentiful regarding fire blight damage in flowering pear, apple, crabapple, cotoneaster, hawthorn, and pyracantha. During March or April, pathogenic bacteria infected flowers or young shoots. Now, shepherd’s crooks (Figure 1) and spur dieback (Figure 2) are becoming more prominent. Often, damage is not noticed until later in the season when branches die completely.
Although symptoms become more obvious during late spring, the fire blight bacterium is not currently active. Hot summer temperatures suppress bacterial growth, and plants are able to compartmentalize and wall off spread. Thus, visible symptoms are the result of early infections.
Current Disease Management
Current recommendations indicate that pruning of blighted twigs and cankered branches should be delayed until winter when risk of disease spread is lowest. Under certain circumstances, homeowners or commercial landscape contractors may choose to prune infected branches during the growing season. Only young, vigorous trees should be considered, and care should be taken to prevent bacterial spread. Always avoid working when plants are wet. Cut branches at least 6 to 8 inches below cankers, disinfesting pruners between each cut (10% Lysol disinfectant, 10% bleach, or rubbing alcohol). Ideally, winter pruning is recommended.
Future Disease Management
Disease management includes both cultural practices and preventative bactericides. Because the fire blight bacterium overwinters in cankered branches, removal of diseased plant tissue before bud break (mid- to late winter) is critical. Copper applied as buds swell (late dormancy or silver tip) reduces build-up of bacterial cells, especially during warm rainy spring seasons. Streptomycin applications are only recommended for fruiting apple and are not labeled for landscape use.
- Fire Blight of Apple (PPFS-FR-T-03)
- Flowering Crabapple (ID-68)
- Homeowner’s Guide to Fungicides (PPFS-GEN-07)
- Landscape Sanitation (PPFS-GEN-04)
By Nicole Ward Gauthier, Extension Plant Pathologist and Kim Leonberger, Extension Associate