Garden Notes: Be vigilant in protecting your trees from Fire Blight
Me: Aw, nuts! Are you serious?
The Arborist: Looks like Fire Blight to me. Sorry.
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Fire Blight is an incredibly destructive disease that attacks members of the Rosaceae family. Penn State horticulture educator Tom Ford said, “Fire Blight can kill trees in an unprotected/unmanaged orchard. Commercial orchards around here protect their trees by spraying streptomycin on their trees while they are in bloom to lessen the blossom blight stage. Commercial orchards typically may spray streptomycin 3 to 4 times while the apple trees are in bloom.”
I’d heard of Fire Blight, but we were looking at a Firethorn (Pyracantha) that had been in the front yard for 30 years. Fire Blight?
Fire Blight bacterium (Erwinia amylovora) is an organism that is spread by wind, splashing rain, insects and us. The bacteria are dormant during the winter.
Then, as the weather warms and becomes more humid, you can see a sticky ooze surrounding a canker on a branch. It starts out with a blight on the blossoms; they look gray-green and quickly turn black. Then the black shoots bend themselves over into a candy cane shape. Given the right conditions, the infection will take over the shrub or tree, making it look as though it has been scorched by fire. The bacterium is especially viral — it’s been estimated it can double itself every 20 to 30 minutes.
Fire Blight bacteria overwinter at the edges of cankers. The only cure is to cut it out. The best time to do the job is during the winter when the bacteria are dormant. To make certain you get them all, examine your trees or shrubs at different times of the day. When the sun is shining from disparate angles, you’ll spot cankers you might have missed.
Check carefully. There is a high risk of canker blight or shoot blight in any new growth. In spring, the tree will be streaming nutrients which will feed the new growth, but nourish the bacteria, too.
Prune the blighted shoots 6 to 12 inches from any canker you see. By doing so, you lessen the chance of the blight spreading to major limbs. Because the bacteria are dormant in winter, disinfecting pruning tools isn’t necessary, but if you’re pruning in trees or shrubs in spring, sterilize the pruning shears with alcohol or bleach before starting and between each cut. It’s a pain, but it will ensure your efforts aren’t spreading Fire Blight to a healthy limb.
Tom advises apple and pear orchard growers to use an integrated pest management approach to control Fire Blight.
He says the most effective practice is to avoid cultivars and rootstocks that are particularly susceptible to Fire Blight. Cultivars like Mutsu, Gala and Jonathan can rarely resist an attack of Fire Blight.
One bad outbreak can result in the death of an entire orchard. Most pears are susceptible too, although Seckel pears are more resistant.
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Me: So, what should I do?
The Arborist: Cut it down, and burn it.
Me: Aw, nuts!
Contact Teresa Futrick at firstname.lastname@example.org