Maine had two bouts of fire blight weather during bloom, one at very
beginning and second at very end. I suspect that the rapid shift to hot
days just before and leading into bloom (after slow cool period from bud
break to pink) may have shocked the trees and resulted in more straggled
bloom than usual.
While we have not had an epic fire blight year comparable to what other
states have experienced in other recent years, there seems to be a
transition this year. Originally fire blight was not a disease that
required attention in Maine. That era ended about 15 years ago. Then,
fire blight used to be something that showed up in a few orchards in some
years, usually but not always relatively minor extent. This year, it seems
that most orchards have a little bit of fire blight. No devastating
epidemics this year, but a lot more than growers want to see.
Following is off the cuff reply to apple grower dealing with fire
blight strikes that keep showing up in Paula Reds. He was wondering if he
can ever dig his way back out of recurring fire blight infections. The
fire blight has been in the block at low level for past 3-4 years and
despite repeated, (though not always immediate) sanitation removal, it is
back again this year. Still not at catastrophic level but it does seem to
be increasing year to year. Rough guess is that this year 20-30% of Paula
Red trees in the block are affected. Most with only one or two strikes,
but a few with considerably more. Unfortunately I think the trees are on
M26. Across Maine. there seems to be much more fire blight on Paula Red
than other cultivars this year. Honeycrisp and Cortland in this same block
hardly affected.
I'm looking for comments. Did I miss any key points? Anything
erroneous? I'm aware of kasugamycin and other alternative materials, but
this wasn't the place for getting into that kind of detail. I don't think
we have strep resistant E.a., should get some more samples tested though.
Is two early season copper applications likely to be any more helpful than
one? Post harvest copper make any sense?
Thanks for your help,
Glen
**************************************
Grower message: "Fire blight looks like heck in the Paula Red’s! We are
just cutting what we can and summer pruning. Is there no hope?"
Reply: " It should slow down with trees ceasing terminal growth. I'm
sure you have other things you'd rather be doing, but getting rid of the
fire blight now will at least cut down work load later, and might be the
thing that prevents further spread that gets to the point where you are
looking at replacing trees.
Copper every spring. Strep on hand so you can react quickly to blossom
blight infection period forecast that you need to check daily because they
can change so fast. Factor fire blight into cultivar and rootstock
selection. Blossom removal on first year trees. Fertility management to
prevent overly lush growth. Consider Apogee where appropriate to reduce
shoot growth and thus shoot blight spread. Daily monitoring and removal of
fire blight strikes starting a petal fall until end of August. Strep on
hand in case hail or strong wind storm creates risk of fire blight spread
(up until strep PHI gets in the way).
Be careful that you don't mix summer pruning and fire blight removal.
They should be handled as two separate jobs. I suspect it would be best
to complete fire blight removal first. Summer pruning before fire blight
removal will create open wound surfaces. Going in after to handle fire
blight material could mobilize bacteria which can infect those wounds.
Thus, better to remove fire blight before creating summer pruning wounds.
Same thing applies to sucker removal. Thoroughly sterilize tools after
using them for fire blight removal before using for anything else. Ugly
stub pruning to allow winter removal of cankers created by sanitation
cuts. Don't leave fire bight cuttings in the orchard as fire blight
bacterial can remain active in dried ooze for 2 years. Burn, bury, or
compost the fire blight cuttings.
It is possible to work your way out of a moderate fire blight
outbreak. But it can take an extended period of sanitation vigilance.
There are no silver bullets."
**************************************
--
Glen Koehler
University of Maine Cooperative Extension
Pest Management Office
Voice: Office 207-581-3882, Cell 207-485-0918
491 College Avenue, Orono, ME 04473
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