Grapevine leaves have yellow spots?

silent88June 4, 2012

I apologize for asking so many questions here but I was wondering if anyone could help me identify what the problem is with my grape vines. There seems to be yellow spots developing on many of the leaves:

And here is the grape vine overall... seems to be growing well. This is happening to both:

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Is that a metal fence, painted black, in the midwest? Doesn't that think heat up to about a million degrees in the summer, burning anything that touches it?

    Bookmark   June 4, 2012 at 9:06AM
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Edymnion, that's something I did not think about. However, I have touched it several times without thinking and never noticed that it was hot... I think there is a thick layer of some kind of paint and I don't think it really gets hot but I'll have to check. Also, the grapevine hasn't noticed and this is it's second year, unless this is a manifestation of the problem. It isn't hot right now, but it isn't sunny so I'll have to check another day. I don't think that's causing the leaves to get yellow spots, though.

    Bookmark   June 4, 2012 at 5:52PM
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Scott F Smith(6B/7A MD)

That leaf pattern looks like downy mildew, look for downy white stuff on the underside of the leaf below the yellow marks to confirm that is what you have. It is common here for me but not so common in California since humidity is usually needed. Google grape downy mildew for treatments.

Don't worry about the metal fence, grapes can "take the heat".


    Bookmark   June 4, 2012 at 6:47PM
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Thanks for the help! I don't see any white stuff on the backside of the leaves, though.

I may have made it worse when I first started my vegetable garden and was spraying the plants (and the wind blew it on my grapes)... didn't realize how bad this was for disease. :/

Here's a few pictures of some of the leaves and the back. The BIG leaf that's really bad is on my big grape vine. Should I remove it?

The other bad leave is on this new vine I just planted a couple weeks ago... :/ It was kind of like that when I got it. I tried to take all the bad leaves off I thought it would be okay.

    Bookmark   June 4, 2012 at 7:23PM
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Scott F Smith(6B/7A MD)

Whatever it is its not that bad a disease. It could be a very mild downy or black rot infection, or it could be some disease I am not familiar with. Someone from California may be able to ID it better... fruitnut, does this look familiar to you?


    Bookmark   June 4, 2012 at 7:34PM
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hoosierquilt USDA 10A Sunset 23 Vista CA

Most likely mildew or something fungal. We've had very cool temps and lots of overcast/marine layer days. I would contact Grangetto's in Fallbrook and send them the photos. They will advise you correctly :-)

Patty S.

    Bookmark   June 4, 2012 at 8:16PM
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Had that before in So. Cal looks like rust to me.

    Bookmark   June 5, 2012 at 5:40PM
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mild chlorosis? The cure would be foliar spray or, if sufficient Fe/Mg are present in the soil, elemental sulphur to be added to the soil.

    Bookmark   June 5, 2012 at 5:55PM
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Scott F Smith(6B/7A MD)

Chlorosis follows the veining pattern of the leaf and this does not. I still think a very mild early stage downy is the most likely, the pictures are exactly how downy starts out. If it has been wet this spring then it also adds up to downy. It could also be some obscure disease that I am not familiar with.


    Bookmark   June 5, 2012 at 9:40PM
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It doesn't look like chlorosis from the pictures I see on google but who knows. I really hope it isn't, that seems much harder to cure.

Is Grangetto's a nursery? I feel a bit bad just contacting them for help if I've never shopped there! but I may do that...

There's one picture on google that seems like it looks similar to rust... only the one leaf with gray looks like it?

Looking at pictures it looks very similar to downy mildew, but like mentioned, it looks like very early stages. Are the brown specks under the yellow spots common in downy mildew as well?

Spring was somewhat wet and foggy for me. My tomatoes got black spot or some kind of fungus disease which, knock on wood, is gone now as far as I can tell. Also I did spray with the hose until I learned better (my poor plants!). Our weather has been much nicer lately and we've had many beautiful sunny days that my plants have been enjoying.

If anyone has any other ideas let me know... but from pictures it really seems like this may be what it is.

Now, is there anything I should do now to cure or manage this issue?

Also, this couldn't be over watering right? We have clay soil not sure how wet it stays.

Thanks so much everyone!

    Bookmark   June 6, 2012 at 7:11AM
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Scott F Smith(6B/7A MD)

If it has since dried up it could be that dried up the downy mildew as well. The brown specks could be the dead mildew. It is very much a humid weather disease. I would keep an eye on the new leaves which should be clean, there is no need to do anything unless the new leaves also start getting infected. There are many sprays for downy, Google will provide good choices.


    Bookmark   June 6, 2012 at 8:17AM
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Downy mildew no question. A number of sprays are available for this (Captan is listed, copper is listed). Spray will CONTROL what is already existing and keep it from spreading and getting worse if done correctly.

    Bookmark   June 6, 2012 at 10:14AM
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