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Alan,
The protectants such as an EBDC or Captan
are non-systemic and actually kill spores as they germinate before they
have a chance to infect the plant. They poison the metabolism of
fungal cells at many levels. Since they are multisite (multi-level)
and fungi would have to develop multiple mutations to overcome them, resistance
is unlikely. So I go for the kill with the first spray since the leaves
are just beginning to grow. At green tip, there isn't much leaf there to
absorb a systemic spray like an SI.
The Strobilurins (Flint/Sovran) have
single-site mode of action and that makes them prone to resistance
development. With Sterol Inhibitors (Nova/Rally) that inhibit different
points in the sterol synthesis pathway, resistance development tends to be
more gradual, but is still possible none the less. Since they are
systemic, they will penetrate the leaf which gives them some "reach back" effect
and I think are better used after 1/2" green.
Right now, Dithane is cheaper than Captan
plus you shouldn't use Captan within 10 days of an oil spray. We always
have issues when we spray oil and try to follow-up with Captan due to the
weather, so that is another reason I choose an EBDC for the first spray in
the years we spray oil. It gives me a bit more
flexibility. Because of the resistance issues, I'm using an
anti-resistant scab management program based on rotating different classes of
fungicides. Here's my timing breakdown:
GREEN TIP - 1 to 2 applications
of an Captan or EBDC (Dithane) at full rate
PREEBLOOM - 1 to 2 applications
of a Strobilurin (Flint or Sovran) or an EBDC or Captan or an EBDC & Captan
(each at 1/2 rate)
PINK & BLOOM - 1 to 2
applications of an SI (Rally - Nova is now Rally) mixed with an EBDC or
Captan (1/2 rate) or EBDC OR EBDC or Captan (full rate)
PETAL FALL, FIRST COVER - 1 to 2
applications of a Strobilurin (Flint or Sovran) OR Captan (EBDC cannot be used
after Bloom)
SUMMER - Classic protectant
except an EBDC such as Captan or Pristine (carboxamide and a
strobilurin)
I'm sure you know all of this, but I went into a
bit more information for the benefit of those who are not aware of the
differences between the various fungicide sprays. I would be interested in
knowing what approach you take in scab management.
Dennis Norton
Royal Oak Farm Orchard Office (815) 648-4467 Mobile (815) 228-2174 Fax (609) 228-2174 http://www.royaloakfarmorchard.com http://www.theorchardkeeper.blogspot.com http://www.revivalhymn.com
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