contributed by George Hamilton and Cheryl Smith
Fire blight, caused by the bacterial pathogen Erwinia amylovora, is found almost every year to some extent in NH and in other apple and pear growing regions of the United States. The annual loss of blossoms and fruit along with the destruction of scaffold limbs make fire blight one of the most destructive of all apple and pear diseases.
Blossoms, twigs, leaves, and fruit can all be infected. Usually the disease is characterized by sudden wilting followed by shriveling and blackening of the blossoms and young shoots. The dead leaves do not fall, but remain on the tree giving the appearance of having been scorched by fire; hence the name “fire blight”. The symptoms are usually first observed following the blossoming period.
Last week, fire blight strikes were seen here in New Hampshire orchards. This week, fire blight strikes are now appearing more extensively with multiple strikes per tree, and more trees are impacted.
What to do if you see fire blight in commercial apple or pear orchards:
• Leave it alone, and if your orchard is hit with a hail storm, apply streptomycin within 24 hours.
• Prune out all infections at least 6” below any visible symptoms during dry weather and wipe pruners with 70% alcohol (do not dip), and refer to the New England Tree Fruit guide for additional management. It is very important to wipe your pruners with disinfectant after each and every cut to avoid spreading the bacteria. Dipping makes you feel good but is not as effective as wiping. You may want to prune with the ‘ugly cut’ method and remove the reminder of the branch during the dormant season, or flag the cut branch to check for cankers during the dormant season.
• If you have newly planted trees with flowers open they should be covered with streptomycin. Warm, wet weather while flowers are blooming is ideal weather for infections.
• Fireblight-susceptible pears and apples should receive a streptomycin spray within 24 hours of a hail storm, even if you do not have any fire blight in your orchard.
• You may need to remove trees that are loaded with fire blight – they will likely die anyway.
Home gardeners should prune out the blighted shoots (disinfect pruning tools between each cut with 70% alcohol). There are NO sprays approved for homeowners to use in combatting fire blight (we do NOT recommend antibiotic spray for home garden use due to the risk of resistance development).