Fire blight is a bacterial infection that has swept across the Wellington community and surrounding area rampantly with nocuous impacts on beloved landscape trees. You will notice the dead and malformed branches, or the “flags” of dried, wilted leaves and fruit, making it look fire-scorched.
Trees in the pome fruit family are the most susceptible to this disease. This includes apple and crabapple varieties (notably the snow crab) and pear trees. It also affects some berries, cotoneasters, Hawthorn and mountain ash trees. Fire blight is spread by insects such as bees, and by splashing rain or contaminated pruning tools. The warm temperatures create an environment for the bacteria to grow and spread rapidly. The severity can be significant, leading to branch die-back and plant death.
Treatment options are few and challenging. There is no single management practice that completely controls fire blight. Chemical sprays such as streptomycin are less effective and only work as a preventative measure. Sanitation pruning in the dormant season can be effective, when being careful to disinfect pruning tools before and after each cut with alcohol, disinfectant, or bleach. It is recommended to prune 10-12 inches below the blight, where feasible. This process can be time consuming and tedious. It is important to be as thorough as possible and to follow up with sanitation pruning across the next few seasons.
Additionally, oxytetracycline treatments, delivered by way of trunk injections, can be helpful with fire blight management for certain candidates. Trees that do not bear a consumable fruit and are 8 inches diameter and greater may qualify for these treatments. It is important to note that once a tree gets fire blight, it will be necessary to continue to monitor with follow up treatments for a few seasons and perhaps indefinitely to be sure the bacteria has been suppressed properly. Replacing trees with resistant varieties can be a realistic alternative, given the cost and complexity of management over a period of time.