A response like the one below by Tim is the reason I subscribe to
this list. An entire course in Fireblight risk in a 5 minute read. Thanks.
At 06:00 PM 7/3/2007, you wrote:
Dear Folks,
There are many aspects of this three-weekly-sprays-yearly approach
to blight management to address, but here are some key points:
1. Yes, fire blight is a difficult disease to control. It isn't
always easy to identify every infection period, except when looking
back at the weather. However, it has been my experience that is
possible to properly identify the more obvious infection periods
that lead to wide-spread damage, or severe problems in a specific
orchard. At times, we predict a significant period of high risk in
the future that doesn't pan out due to cooler than predicted
weather. But it has been very easy to see the actual significant
infection periods that happened over the past 20 years in the
Pacific Northwest. Sometimes you don't even need a model, the
infection risk is obvious to any alert grower. Three or four+ days
in the high 70's or 80's F while the trees are blooming, followed by
rain or dew? Who needs a model for that? These "way too
complicated" models have been designed for growers that care enough
to try to make informed choices.
2. People who take the time to understand a problem (such as fire
blight) are more likely to avoid it. That doesn't mean that you
won't have fire blight if you understand it, just that you might
avoid a serious outbreak on the infrequent bad years. We see this
often. The growers who spray on time may misjudge the need to spray
once in a while, but they usually avoid serious blight on the bad years.
3. Blight happens almost everywhere where the pathogen has spread,
but it occurs infrequently, which is a problem. If you are in an
area where it happens once or twice a decade, it is difficult to
stay tuned in every year. It's a great pathogen, and we are growing
susceptible hosts, some much more susceptible than others, but no
apple or pear is more than tolerant.
4. Spraying on a fixed schedule every season is a waste of a rare
resource. It is possible that a scheduled blight spray would be
applied by chance at a correct time, but why avoid choosing the high
risk period as a better time for treatment?
5. It is almost impossible to gain agricultural registration for a
truly effective antibiotic, and very few candidate materials
exist. We are not allowed to test products that have significant
importance in either human or animal health, which greatly reduces
alternatives. We have streptomycin, which is (or was) the best
product ever for fire blight control; oxytetracycline, which works
for us out here in the Pacific Northwest, but is panned everywhere
else; Gentamycin (how you got that special label in Michigan!? Good
work, George!), and Kasugamycin, which may gain a USA label, but we
shall see. All of these, except oxytet., have a real risk of rapid
loss of effectiveness due to bacterial development of
resistance. Within most populations of Erwinia amylovora,
scientists can identify a few bacteria resistant to these
antibiotics (except oxytet.) Willy-nilly application of the product
just speeds up the process of selecting out those resistant
individuals, allowing them to dominate the colony. We need to have
more than one fire blight control material, so that we can try to
help growers rotate product use. The EPA and The Centers for
Disease Control would rather that we had no antibiotics available,
so we compromise by having only one effective product for any specific area.
6. Primary infection occurs through open flowers. The pathogen
seems to have adapted to that, so is rarely found outside of the
dormant tree, and is unusual until just prior to blossom time. Even
if the canker "wakes up" prior to blossom opening, the streptomycin
does not act like some sort of antiseptic, sterilizing the
tree. Even copper, which has a more direct action on the bacteria,
is often questionable as a pre-bloom treatment. We do not expect
antibiotics to do anything other than control of blossom
infection. You are wasting your time and money applying antibiotics
unless your target is a flower at risk. Applying an antibiotic more
than 24 hours after an infection event has been a common mistake.
7. I have never documented a blight outbreak where infection was
initiated during a period of cool weather, however wet. If this was
possible, why don't we see blight everywhere, every year?
Timothy J. Smith
WSU Extension,
Chelan, Douglas & Okanogan Counties
-----Original Message-----
From: [email protected]
[mailto:[EMAIL PROTECTED] On Behalf Of George M. Greene
Sent: Monday, July 02, 2007 8:31 PM
To: Apple-Crop
Subject: Re: Apple-Crop: Fire Blight
David:
Spraying Strep 3 times a year does not sound like modern IPM based
pest control. May I suggest that you, instead of spraying so much,
hire a consultant with money that you would have spent on Strep.
Also, I'll let a plant pathologist respond but I'm wondering if
excessive use of Strep will eventually result in Strep resistant
fire blight organisms.
George Greene
>Hello everyone,
>I have had a nasty recurrence of fireblight this year. I was trying to
>"cheat" the disease. There was no rain and no warm temperatures during
>bloom. Nevertheless, it snuck in on me probably from dew and moderate
>temperatures. I cannot believe the models. It is way too complicated to
>follow the models and pump in the facts especially during that busy
>season.
>Believe me, - I will never let this happen again. In the future I am
>going to inoculate the orchard with strep during pre-bloom, bloom and
>post-bloom period, no matter what the forecast is to be.
>My Dad said that when he had his orchard in Arkansas, - everyone had
>fireblight problems, - except him. He just went out and sprayed strep
>every week (or less). Now that is a warm, humid climate. He said that
>if he observed some strep toxicity (white mottling of the young leaves)
>he knew the trees were protected.
>
>David Barclay
>169 County Rd. East
>Colts Neck, New Jersey 07722
>
>Phone: 732-544-9035
>Fax: 732-542-7855
--
George M. Greene II
68 Willow Lane
Wiscasset, ME 04578
[EMAIL PROTECTED]
207-882-8074
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Decorah, Iowa
"Various forms of religious madness are quite common in the United
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