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[<dmnorton@royaloakfarmorchard.com>]



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

----- Original Message -----

From: Alan Haigh

To: nafex@lists.ibiblio.org

Sent: Thursday, March 19, 2009 5:26 AM

Subject: [NAFEX] Dennis's oil spray advice

Dennis, your explanation of oil application was comprehensive and articulate- I made a copy for my files.  I have a question- why do you prefer using an EBDC over an SI in early spray?  I can't see the advantage to mancozeb over say, myclobutinil.