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Thursday, March 22, 2018

Cool Wet Spring Perfect for Fireblight

Bacterial diseases like fireblight need openings to enter the susceptible plant. Flowers provide temporary openings and let this disease enter inside plants. So do fresh pruning cuts. Fireblight disease spreads from infected to uninfected plants through these openings. Rainy and windy weather helps spread this disease when flowers are open. Honeybees are suspected to spread this disease as well by visiting these flowers.

Cool, rainy weather when pear and apple are in bloom, is perfect weather for fireblight disease. Fireblight is a very aggressive and dangerous plant disease that shows up as new infections in about May in Asian Pear, European pear like Bartlett and some apples. It can be a major problem on Quince as well.
This is why the first evidence of fire blight disease is usually seen by the blackening of the flowers in late spring. From here it can spread into branches and cause severe problems.
            But the disease problem, although unseen, can begin now. The point of entry for this disease into susceptible plants are the open flowers and fresh pruning cuts. Open flowers and fresh pruning cuts provide “fresh wounds” or points for this disease to enter inside the plant. Wind and rain are the usual culprits that spread the disease from plant to plant but even honeybees can be responsible.
Fireblight has spread from a flower or pruning cut and caused more dieback.

            If this disease is seen early enough (usually in late April or May) it can be eliminated easily with a few snips of a sanitized hand pruner, eliminating the infection. But the hand pruner must be disinfected between each cut on the tree or the disease can be spread on the hand pruners through each cut.
Classic textbook dieback and progression of fireblight disease

            There is some disagreement about what to use to disinfect hand pruners but chlorine bleach seems to be the favorite among orchardists. Heat from the open flame a cigarette lighter also seems to work. Some people suggest alcohol and others suggest household cleaners like Pine-Sol.
            Plants that were infected in previous years will show evidence of this disease when new growth occurs in the next couple of weeks. As the name suggests, this damage resembles the black from fire damage. This can be confusing because any damage to pear leaves can turn black. If you are unsure, send me a picture.

            We have had a surge in this bacterial disease over the past few gardening seasons because of our cool wet springs. I will post more pictures of this disease from past years on my Internet blog, Xtremehorticulture of the Desert.

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