I should be at 4 sprays or less (3 last
year) most of the time. The six sprays occurred after the "year
without a winter" several years ago, when the low for the entire
winter was 15F and that was only reached twice. We were 5 below
here last year, and normally get plenty of consistent chill hours,
which results in a uniform bloom. The need for alternate products
will not be common. We're reaching tight cluster here this week,
and projected bloom looks very consistent and uniform. In future
years, when Kasumin drops in price and becomes more available, I
think it might be a good option if a protracted bloom shows up
again. I should mention that this problem has been unique to Pink
Lady/Cripps Pink as its low chill requirement makes it a blooming
machine. It is however the best apple we grow here, and it stores
very well along with Fuji and Goldrush.
Fascinating stuff: the transfer of DNA from other bacteria. I had
no idea.
On 3/23/2015 9:44 AM, David A.
Rosenberger wrote:
I should have added one
more thought: Probably the very best strategy for avoiding
selection for strep-resistant Erwinia amylova (Ea) is to prevent
fire blight from becoming established in the orchard in the
first place. To that end, the integrated strategy that Brian
described (copper early, strep as required by a timing model,
and Apogee to make shoots more resistant) reduces the likelihood
that he will ever have visible fire blight or even high
populations of Ea in his blocks. You can’t get resistance if the
pathogen of interest never becomes established, even if
non-Erwinia species in the sprayed blocks may have detectable
levels of strep-resistance.
Thanks for the
follow-up information, Brian. Using six strep sprays
during bloom, while I can see how it may be necessary,
does make me a bit more uneasy about selecting for strep
resistance. In northeastern United States, we often
need two sprays during bloom, sometimes three, and very
rarely four. I’ve not been concerned about using four
sprays if needed. However, I doubt that anyone has
enough experience with the impact of 6 early-season
sprays to be certain of the outcome.
One theory about
how strep resistance develops (and I think this is still
valid) is that the initial selection for resistance is
not in Erwinia, but rather in other bacteria that exist
in the orchard environment. These other bacterial
species may then pass on the strep-resistance genes to
Erwinia because bacteria have mechanisms for
transferring useful DNA (i.e., DNA that enhances
survival) from one species to another. When strep is
applied to apple and pear flowers in springtime, the
over-all bacterial populations on leaves and in soil are
still rather low because bacterial population build
slowly as plants and soil warm up. Therefore, there is
less selection pressure for resistance in the
non-Erwinia species when strep is applied during bloom
as compared to after bloom. Bacterial populations in
the orchard environment increase very rapidly as
temperatures rise, so summer applications of strep
impact a much larger universe of bacteria and therefore
are presumed to be more likely to trigger resistance
that can later be transferred to Erwinia.
Strep is broken
down in sunlight, but each application may contribute to
residual accumulations in the ground cover, duff, or
soil surface where the accumulation from multiple
applications might persist long enough to enhance
selection for resistance in soil bacteria as soil
temperatures rise. I really don’t know how long strep
persists in orchard soils, and there is undoubtedly huge
variations depending on rainfall, orchard cover, soil
type, etc.
I’m sending this
post simply to indicate that there is still a lot of
things we don’t know about how our agrichemical products
impact the total orchard environment. Given that
uncertainty, I’m still willing to bet, based on our
history in the Northeast, that limiting strep
applications to blossom time in areas that average only
two or three strep sprays per year will never result in
selection for strep resistance even if growers
occasionally use one additional application after bloom
to suppress trauma blight following hail or wind storms.
However, if you will need more than four strep sprays
on a regular basis, that makes me a bit less comfortable
and you may want to break up that string of strep sprays
by including Kasumin in your blossom spray strategies.
No
resistance from bloom sprays is good news. I have
had no control problems with copper prior to green
tip, strep timed by Maryblyt, Apogee to minimize
pruning/harden shoots to possible shoot blight,
and control of aphids/leafhoppers at petal
fall/1st cover. A few years ago, however, we had a
long, extended bloom with Pink Lady. Maryblyt
called for a total of 6 sprays (predicted EIP over
100), which exceeds most recommendations of 4 max.
I went with the 6 applications and came out OK,
but have always wondered if this might trigger
resistance. I will stick with strep during bloom
and leave the Kasumin for those that need it. I
did just put in a block of CrimsonCrisp and
haven't thought about putting copper on them. Good
advice. Thanks.
On 3/21/2015 10:36
AM, David A. Rosenberger wrote:
While Kasugamycin works about as well as
streptomycin, oxytetracycline is generally a bit
less effective and has the disadvantage of
preventing bacterial multiplication without
killing off all of the bacteria contacted by the
spray. Of the three antibiotics, it is my
understanding that only strep is absorbed into
apple tissue, thereby giving it a bit of an edge
over both of the other products, especially in
cases where a few infections might have been
initiated a few hours before the product is
applied. Kasugamycin, like strep, kills
bacterial cells that it contacts, but it has the
disadvantage of being considerably more
expensive than strep.
Some of my pathologist colleagues
may disagree with me, but I see no reason to
pay the extra price for kasugamycin in
established orchards that have no history of
strep resistance. (An exception would be in
countries like Canada where the strep labels
allow a maximum of 3 applications/yr.) In
eastern New York and New England, we have used
strep exclusively for fire blight control for
more than 60 years without encountering
resistance. Resistance to strep has only
appeared in regions where nurseries or fruit
growers have used it repeatedly during summer
(as many as 12 times/yr) to prevent shoot
blight. Thus, there is an abundance of
observational evidence that repeated
applications of strep after bloom DEFINITELY
WILL result in strep-resistant Erwinia
amylovora (Ea) whereas, so far as I know,
there is absolutely no evidence that multiple
applications during bloom have ever resulted
in strep resistance. Thus, I would argue that
strep is still the cheapest, most effective,
and most proven product for controlling
blossom blight, and I see no reason to use
other products except where strep resistance
has been documented or is suspected due to
failure of well-timed strep sprays. In fact,
alternating with biologicals or with oxytet
may actually be counter-productive because
they may allow more bacteria to survive,
thereby leaving larger populations to be
controlled by strep and/or allowing some
infections to become established and thus
carry the disease through until the next year.
Given that there is increasing
evidence that fire blight is sometimes present
in symptomless nursery trees, one could argue
that strep-resistance may show up anywhere as
a result of distribution via nursery trees.
This is a very real and valid concern. To
diminish the likelihood that strep-resistance
might be introduced with nursery stock, we in
NY have been recommending that all newly
planted trees be sprayed with copper shortly
after they break bud and then with copper plus
strep during bloom. The basis for this
recommendation is that copper should knock out
strep-resistant Ea on plant surfaces whereas
strep will still be more effective for
preventing local sources of Ea from infecting
flowers on newly planted trees. Using several
sprays of Kasugamycin on newly planted trees
when they produce flowers during the first
year of planting might be even better than
copper plus strep for preventing establishment
of strep-resistance brought in with nursery
stock. Finally, it should be obvious that all
new apple plantings should be observed very
carefully for evidence of fire blight symptoms
for several months after the trees begin to
grow, and any diseased trees should be removed
immediately.
We probably had more fire blight
in newly planted trees in 2014 than in any
prior year, but it is not a new phenomenon. I
ended up with some blight-infested nursery
trees in 1986 when I was establishing one of
my research orchards. Both in that 1986
situation, rapid removal of diseased trees as
they showed up during the year of planting
prevented blight introduced in nursery trees
from becoming established in my research
blocks, and the remaining trees were
completely disease-free in subsequent years.
However, last year some growers opted to
remove all newly planted trees when they found
significant percentages of the trees were
developing fire blight because it was unclear
whether they could successfully identify all
of the trees that were carrying the disease.
Hopefully there will be less blight in nursery
stock in 2015.
********************************************
Dave Rosenberger, Plant Pathologist,
Hudson Valley Lab, P.O. Box 727, Highland,
NY 12528
Cell: 845-594-3060
http://blogs.cornell.edu/plantpathhvl/blog-2014/
********************************************
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Brian Heatherington
Beech Creek Farms and Orchards
2011 Georgia Highway 120
Tallapoosa, GA 30176
770-714-8381
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Beech Creek Farms and Orchards
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Tallapoosa, GA 30176
770-714-8381
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