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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