Fireblight on Pear Trees

    • Feed camellias, azaleas and rhododendrons with an acid plant food now. Remove dead flowers and mulch to keep the soil cool.
    • Plant fresh herbs from young plants. Basil, rosemary, thymes, mints and sages are just a few ideas.
    • Check roses for black spots on the leaves and treat immediately to prevent defoliation.
    • Hydrangeas have giant pink or blue flowers. They will brighten the shade garden all summer.
    • Meyer lemons, with their sweet-scented blossoms, are attractive and easy to grow. Plant one in a container so you can move it to a protected spot in the winter.

Fireblight on Pear Trees

“The last time you went out to check on your orchard, the pear trees were setting fruit and everything seemed fine. But all of a sudden, it looks like someone took a torch to whole branches of it and now the tree looks dreadful.”

If this sounds familiar to you, chances are your pear trees have fire blight. Fire blight is a destructive disease common on pear, Asian pear, quince and sometimes apple trees. It also affects pyracantha, cotoneaster, hawthorn and some other related trees and shrubs. The disease can destroy limbs and even entire shrubs or trees if left unchecked.

Fire blight actually starts in the spring with a light ooze from cankers on branches, twigs, or trunks. The ooze turns dark after exposure to air, leaving streaks on branches or trunks. However, most cankers are small and inconspicuous and infections may not be noticed until later when flowers, shoots, and even young fruit shrivel and blacken.

The infection usually enters through the flowers and then moves down the branches, infecting fruit, leaves and stems as it goes. Dead, blackened leaves and fruit are the result which give the tree a scorched appearance, hence the name “fire blight.”

In warm, moist spring weather, the disease becomes active and usually infects the blossoms if it rains while the tree is blooming. This year it seems that conditions were perfect for fire blight, and we are seeing a lot of customers with this problem.

Once it has infected a tree, the only thing to do is to prune it out. You must prune at least 8 inches below the damage. This often means also removing a larger branch to which the infected branch is attached. This is necessary because the infection spreads down into the tree ahead of the visible portion.

Dip pruning tools in 70 percent isopropyl alcohol (rubbing alcohol) or 10 percent bleach solution (1 part bleach to 9 parts water solution) between each cut. Wash and oil shears when you are finished. Dispose of all infected plant material.

Next winter, you can spray your trees to help prevent fire blight. Copper sprays can be used before bud break – when leaves emerge from the buds. Streptomycin (an antibiotic) can also be used from bloom through petal fall period to prevent infection from occurring. Repeat the spray at 4-day intervals through the bloom period, but do not apply streptomycin when the maximum daily temperatures are below 65°F.

Any excessive amount of new growth on your tree is easily susceptible to fire blight infection, so use only low-nitrogen fertilizers on susceptible trees. Be sure to completely clean up around your trees this fall, picking up any dead twigs and mummified fruit on the ground, and disposing of them.

This has been a particularly bad year for fire blight in California. Trees bloomed early, and warm, moist weather spread the disease rapidly. Pruning is your best option to control the disease this year.

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