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/
********************************************
On Mar 21, 2015, at 7:18 AM, maurice tougas
<appleman.maur...@gmail.com<mailto:appleman.maur...@gmail.com>> wrote:
Would oxytetracycline be an effective economical alternative in those
"borderline" instances?
Mo Tougas
On Fri, Mar 20, 2015 at 10:18 PM, Smith, Timothy J
<smit...@wsu.edu<mailto:smit...@wsu.edu>> wrote:
HI Brian,
Yes, that would work well. Kasumin has worked well in Michigan.
Tim
From:
apple-crop-boun...@virtualorchard.net<mailto:apple-crop-boun...@virtualorchard.net>
[mailto:apple-crop-boun...@virtualorchard.net<mailto:apple-crop-boun...@virtualorchard.net>]
On Behalf Of Brian Heatherington
Sent: Thursday, March 19, 2015 1:29 PM
To: Apple-Crop
Subject: [apple-crop] Kasugamycin for fireblight
Planning ahead for bloom:
In an area where fireblight is still effectively controlled by streptomycin,
would it be advisable to rotate to kasugamycin for one or more sprays, purely
for resistance management? Perhaps when models show a borderline need for
application? How effective has Kasumin been in Michigan?
--
Brian Heatherington
Beech Creek Farms and Orchards
2011 Georgia Highway 120
Tallapoosa, GA 30176
770-714-8381<tel:770-714-8381>
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--
Maurice Tougas
Tougas Family Farm
Northborough,MA 01532
508-450-0844
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