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nafex - [NAFEX] Antibiotics and Fireblight

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  • From: "Dr. Ethan Natelson" <natelson@pipeline.com>
  • To: nafex@lists.ibiblio.org
  • Subject: [NAFEX] Antibiotics and Fireblight
  • Date: Wed, 05 Mar 2003 07:10:22 -0500

Dear Rodney,

The offending bacteria, Erwinia Amylovora, is actually quite sensitive
in the test tube to many different antibiotics, including the tetracyclines
and streptomycin. The problem is getting the antibiotic into the vascular
system of the tree with a superficial external spray application. Thus,
when you see obvious blight, an application may not be all that much help.
The sprays work best when the tree looks fine but is in blossom and the
flowers may be carrying a high innoculum of bacteria, or following a hail
storm when there is superficial bark damage and potential for wound
infection. When you see some infected branches, immediate and judicious
pruning is the best remedy.

Here in Houston, at times I have used both antibiotics, but it is
difficult to know with certainty when you have had success from them or if
it was simply a low fireblight year. One of our most sensitive pear trees
to blight is Spaulding, and most people here who have planted this one have
dead trees. Mine, now about 10 years old, and which is occasionally sprayed
but frequently pruned when blight becomes evident every year, looks great
and is in full bloom right now. I don't know if my success is the rare
antibiotic spray toward the end of flowering or the pruning.

Regards, Ethan




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