What you are describing with the lesion -- the raised black dots = sounds
exactly what we see with Marssonina infection. Depending on when you sprayed
captan and how much rain you received afterward (i.e. washing off the captan),
this could have been the entry point for Marssonina. I noticed Marssonina on
my trees that I sprayed conventionally all season; however, we stopped spraying
captan at the beginning of September...and we had close to 15 inches of rain
fall during the month. And we never reapplied...consequently, Marssonina
showed up. Although captan keeps the disease in check, you need to keep in
mind it will wash off with 1-2 inches of rain and needs to be reapplied.
Kari
Penn State
________________________________
From: apple-crop-boun...@virtualorchard.com
<apple-crop-boun...@virtualorchard.com> on behalf of David Kollas
<kollasorchar...@gmail.com>
Sent: Tuesday, October 9, 2018 7:52:30 PM
To: Apple-crop discussion list
Subject: Re: [apple-crop-2] Apple leaf disorder
Dan, Brian, Kari, Mo, and others:
Having read your comments and links, I looked more closely at my
symptoms. I was wrong about its association with yellow delicious breeding. I
can find it in Macoun, Empire, and many others. The symptom common to all that
I looked at with magnifying
glass was scattered dark blackish raised dots in the live or dead “spot” that
often retains its green color after surrounding areas have
yellowed. I did not find any affected leaves that exhibited the concentric
bands noted in the 2012 blog, with click-enlarging photograph, by Dave
Rosenberger on Glomerella leaf spot. Therefore I conclude it is not Glomerella
infection. If it is Marssonina leaf spot, I would
not expect it to have survived all the captan sprays I have administered. Sooty
Blotch and Flyspeck, in spite of all the favorable
conditions for those diseases, are rare here at this time. I suppose it could
have a physiological cause that made areas of the leaves
susceptible to opportunist fungi, and some petri dish work in a lab might
isolate and identify those raised black dots. It is discouraging
to loose the leaves before harvest, not knowing why, nor what could have been
done to avoid it,
David Kollas
>
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