Grapevine fungus?

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havlikn

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Attached are two pictures of a Frontenac grape leaf. The vines have been sprayed on a 10-14 day interval with manzate and pristine. I can't tell if this is representative of black rot or is some sort of nutrient deficiency or something else. The berries are not showing any sign of disease in regards to black rot. Thoughts?
 

FrontenacMan

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Hi Havlikn,
Sorry I'm a little late to the party. I just now tripped across this post and thought I'd contribute since I'm in your neck of the woods. I too experienced this on my Frontenac but only on selected vines and not on my Frontenac Gris. I did lose some fruit clusters. I surmised downy mildew due to the excessive amount of rain we had this year. I thought this leave problem might be related. Just my theory. I don't use any fungicide. I'm judging based on last years harvest which was much better than this year. I just think it was not the best year for grapes this year in WI (or tomatoes either ironically) because of all the rain/moisture. I assume you know that the gaping holes in the leaves are probably Japanese Beetles. I battle those every year too. I've been applying Sevin about every two weeks since mid-July. My fruit is beginning to ripen now but several clusters have damage. I did not have this problem (fruit loss) last year. I just put up bird netting as the birds seem to be getting interested in the fruit now that it is sweetening up.
 
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