For years I could not feel confident that Sooty Blotch/Flyspeck would
not appear late in the year, beginning about
the time of Macoun apple harvest. That was a serious problem, because I did not
understand how the disease developed
and how to prevent appearance of symptoms. Now it seems that what we are
calling Marssonina blotch could be as
difficult and damaging as was Sooty Blotch/Flyspeck before I learned how to
control it.
What is different about Marssonina that it is not controlled with the
program of captan plus phosphorous acid that
results here in a harvest nearly absent of Sooty Blotch/Flyspeck? Are initial
infections of Marssonina not inhibited from
progressing in the presence of effective fungicide? Does the shorter time for
infections- to- visible -symptoms
(45 hours for Marssonina versus 270 hours of wetting for SB/FS) account for the
control failure? Is development of resistance
to captan involved?
Yesterday I spent time reviewing my spray records for this year, and
reading more about Marssonina. I should have
been out in the rain picking, transporting, and shuffling apples around in the
cold storage. Just one fungicide application
was made in June (June 1) and it remained nearly rainless until the June 23-28,
when 3.4” fell. Fungicide sprays re-
commenced July 3, repeating July 15, 20,26, August 5, 15, September 7, 14, 23,
27, and October 6, in advance of predicted
rains. In seven of those wet events, rain exceeded two inches, and
re-application of fungicide was delayed for one or more
days waiting for suitable application weather (light wind, not raining).
David Kollas
> On Oct 10, 2018, at 11:42 AM, Daniel Cooley <mailto:dcoo...@umass.edu>> wrote:
>
> I agree with Kari’s analysis. Sounds like Marssonina. Bring or send some up
> if you’d like.
>
> Dan
>
>
> —
> Daniel R. Cooley, Professor of Plant Pathology
> Stockbridge School of Agriculture
> 418 Paige Lab
> 161 Holdsworth Way
> University of Massachusetts, Amherst, MA 01003
> Office Phone: 413-577-3803 | Cell: 413-531-3383
>
>
>
>> On Oct 9, 2018, at 7:52 PM, David Kollas > <mailto:kollasorchar...@gmail.com>> wrote:
>>
>> 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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