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Re: MEDIT-PLANTS digest 609

>Help!  The branch tips of my evergreen pear and fruiting pear trees are black
>and singed looking - I assume this is fire blight?   What can be done to for
>fire blight?  Will the trees die?  Is pruning the answer - and do I need to
>sterilize the tools afterwards?  Any advice would be appreciated,
>Carolyn Lawrence  (CZLAW@aol.com)

Caution.  Don't jump to conclusions.  You say the branch *tips* are
blackened?  Fireblight enters through flowers and can spread to the tips
but more often spreads inward so that the end of the branch may be
untouched while interiors areas are dead-looking.  Check to see if your
*flowers* are blackened.  Does each infection seem to start from a flower?
What part of the world are you from?  What is the prevalence of fireblight
in your geographic area?

*If* it turns out to be fireblight(*Erwinia amylovora*) there is some
disagreement among scientists about the necessity of sterilizing tools
between cuts.  It's probably a prudent thing to do but, since the infection
only spreads through flowers it's unlikely you'd spread the disease further
by pruning when there were no open flowers.  The usual recommendations for
*Erwinia* is,

1.  Prune *6 inches below* visible infections sites.  I've found this to be
less than effective.  It's likely that there are other infected trees in
your neighborhood.  If bees found you this year they'll likely repeat the
process year after year.  After a while you'll find your pear tree is
little more than a stick following your annual pruning.  You won't want to
hear it but it would probably be smartest to buy a resistant cultivar next
winter with the idea that the resistant tree will eventually replace the
susceptible one.

2.  Spray with bordeaux mixture at time of bloom.  I find this *very*
tricky.  Pears typically don't oblige by flowering all at one time so
you'll likely be out there every couple of days for a fortnight.  It's also
tricky to apply the gooey bourdeaux without disrupting pollination.

3.  Professional landscapers can procure bactericides like streptomycin
that do a good job on the disease but be prepared to feel guilty for making
your little contribution toward making the world's bacteria resistant to
antibiotics thereby.

4.  The Rodale people list lots of resistant pear cultivars including:
Asian Pears, Comice, Dawn, Douglas, Duchess d'Antouleme, El Dorado,
Fan-stil, Lincoln, Luscious, Mac, Magness, Maxine, Moonglow, Orient,
Seckel, Starking Delicious, Sugar, Sure Crop, Waite, Winter Nelis.  They
add this reassuring note: "A variety's resistance depends to some extent on
local weather conditions during bloom, the proximity of trees with
cankers{the disease overwinters in small cankers on the bark}, and the
number of insect carriers in the area."  Thanks a lot.

5. Sanitation is essential.  Pick up *every* bit of fallen leaf and bark matter.

6.  A stealth attack on all neighborhood rosaceous species with a sharp saw
might decrease your chances of reinfection.  Keep a good lawyer handy.

7. Don't fertilize your trees as that encourages the disease's spread.
Like all bacteria it spreads in water(i.e. rain is bad news).
Jerry Heverly, Oakland, CA
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