Do you see patches of dark, almost black foliage on your ornamental pear trees? Are the branch tips turning black and wilting into a “shepherd’s crook shape? Are the fruit turning black, shriveling and falling off? Chances are your trees are suffering from fire blight. It’s a very common disease of ornamental pear trees like Bradford and Cleveland Select, as well as orchard trees like apple and pear. Fire blight is especially common when spring and early summer are particularly hot and humid,
Fire blight is caused by a bacteria called Erwinia amylovora, which affects apple and pear trees as well as other edible fruits such as raspberry and quince. As bacteria spreads throughout the tree, it may push up through cankers or sores in the bark that ooze sticky sap. Insects spread the sticky, bacteria-filled sap to healthy trees, infecting them through flowers, pruning cuts or cracks in the tree bark.
Most pear varieties are somewhat susceptible to fire blight, although some varieties of fruit trees are bred to be more resistant. The trick to managing fire blight is to watch for signs of it on your pear trees and treat it promptly, before it spreads. If you notice fire blight on your pear trees, you can take several steps to prevent it from spreading or claiming the life of your tree:
Prune out signs of disease during the summer and during the dormant season. Make cuts 8 to 12 inches below the last sign of infection to remove all potential sources of infection. Wipe your pruner blades with rubbing alcohol or bleach between each cut, to prevent the spread of bacteria. Burn fallen leaves and diseased shoots, or bag and discard them in the trash, not in the compost pile.
Avoid using nitrogen-heavy fertilizers, which encourage rapid shoot growth on trees. Rapid shoot growth seems particularly vulnerable to fire blight. We like Espoma Tree Tone®, a slow-release, low-nitrogen fruit tree food supplement. Well-nourished, healthy trees are more resistant to any sort of pathogen or insect than stressed, undernourished trees.
It is almost impossible to prevent fire blight in pear trees, but good housekeeping helps. Rake up and discard diseased fruit and fall leaf drop. You can reduce new infections by spraying an antibiotic such as streptomycin sulfate (Ferti-lome® Fire Blight Spray) on flowers or shoots early, at bud break in early spring. Spraying with copper sulfate fungicide (Bonide® Copper Fungicide) can help, when applied several times while the blossoms are open. Neither option will eliminate infections already existing in the wood.
Fruit orchards should be sprayed regularly, particularly in spring when they are sprouting new growth, with all-purpose orchard spray. Control for insects with sucking mouthparts that can easily spread the bacteria. This includes controlling for aphids and pear psylla. Commercial orchards are sprayed every 10 days to 2 weeks during the growing season, but the spring applications do the most good.
Commercial orchards infected with fire blight are often treated with antibiotic sprays, but these are expensive and potentially too costly for home gardeners. By trimming out diseased branches, cleaning your tools between pruning sessions, picking and discarding diseased fruit, and monitoring your trees regularly, you can take many steps to minimize the impact of fire blight on your pear trees. You may not be able to avoid it entirely, but you may be able to save your trees so they can flourish for many years to come.
Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are online at www.goodseedfarm.com. For more information call GoodSeed Farm Landscapes at (937) 587-7021.