Which disease is this and what do I do???

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gcook1

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Hi everyone
I have a small 3/4 acre vineyard I inherited from my father-in-law. This is my 3rd summer and I'm having a problem with what I think is downy mildew but I'm not sure. I've attached a couple pics of the leaves. I have four varieties of wine grapes... Marquette, Foch, Chambbourcin and Chancellor. I'm mostly having an issue with one variety. It's either the Chambbourcin or Chancellor... my FIL didn't document which is which.

I've sprayed 3 times this season:
6/3 - Captan 50 and Rally
6/20 - Captan 50 and Sovran
7/2 - Captan 50 and Rally

Is that downy mildew I'm getting hit with? Should I be doing something different?

Thanks for any ideas!

Leaf1.jpg

leaf2.jpg
 

havlikn

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Personally I think it may be a nutrient deficiency. I have a buddy that had vines like that last year and added a 10 10 10 fertilizer this year and it is not appeared at all.
 

jgmillr1

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I have Chambourcin also and have experienced similar spots on it in previous years. This year the leaves do not exhibit any of these spots and I attribute that to a more aggressive spray program. Since bloom (around Memorial Day) I have been spraying at least weekly with mancozeb along with a spreader/sticker. I added Rally into the spray program mid June and am transitioning to Captan in place of mancozeb.

My main goal was to protect against the black rot issues that I had in previous years due to our wet June weather. While there still is some black rot this year (just upgraded to a more effective sprayer), one side effect is that the leaves are free from these spots.

Last year I applied fertilizer at the end of May and ended up with leaf spots anyway. This year, I missed that window and did not apply fertilizer.

Anyway, the response of my Chambourcin suggests that the spots are a fungal issue that mancozeb prevents. I believe most nutrient deficiencies usually present themselves as a discoloration of the leaf that follows the contours of the veins.
 

balatonwine

The Verecund Vigneron
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Could be nutrient problem (potassium for example), or fungus. Any other symptoms, such as on stems or berries to help diagnose?

For what it is worth, both powdery and downy mildew can become active and infect leaf tissue at or above 50°F if proper moisture conditions are present. So your first spray in June may be a bit late to protect young leaves, which if were infected in May may start to show brown lesions about now.
 
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