Grapes Vines Curling Leaves & Little Black Spots

bourbonladyMay 30, 2007

This is the second year for our grapevines here in central Oklahoma right on the border of zones 6 and 7. Last year we didn't have a single problem, but this year, within the last week, on 3 out of 6 of our vines, we are having leaves that are curling and then on the underside, tiny black spots. On one of those three vines, we also have "burnt" areas on the leaves. The varieties are fairly common, Ruby Red Seedless and Thompson Seedless, two were bought as more mature plants ($45 each) and the other younger ($15.)

We had major drought and high high temperatures (several days well above 110) last summer and their roots have spread wonderfully. This year, thus far, we have had right at 20" of rain in the last 90 days, with a little over half of that hitting within the last 30.....and more to come every day the rest of this week...... It has also remained slighty "cool."

I have only found one other posting similar regarding curling leaves on grape vines and it referred to possibly aphids. The black spots on the leaves are not moving and are not bumpy, more or less ingrained in the leaves. I have searched and searched the vines and find no signs of any insects with the exception of very tiny white flying things. We did apply seven dust last week, which is the only thing we've attempted thus far.

Our gardening experience is the old fashioned, trial by error method, so frankly, we probably don't really know what we are doing!!!!

Thanks is advance for any help!!!!! Photos of the leaves and vines are in the link below:

Here is a link that might be useful: Photos of Grape Vines & Leaves

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Scott F Smith(6B/7A MD)

The bottom picture I would say is almost certainly black rot. Use Google image search and compare the pictures you find there. Those little black spots are benign in some varieties, my Chambourcin always has them. Or maybe they are small spots of black rot? I don't know about the leaf curling, many things can do that. I would look carefully for signs of bugs or other disease -- leafhoppers and powdery mildew are two potential causes of leaf curl.

What have you been spraying? Those grapes are vinafera types and are not disease-resistant at all. I spray my vinafera every week this time of year. Black rot is one of the worst grape diseases, it will cause all of the fruit to rot. If you don't have a regular spray program you need to do some research and set one up. Or pull those varieties and try some more disease-resistant ones.

Scott

    Bookmark   May 31, 2007 at 8:46AM
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bourbonlady

Thank you so much, it's tough to search for a cure if you don't even know the problem. Black Rot fits perfect with the symptoms and conditions. Still not sure about the leaf curl and black spots......

We have only sprayed with Seven once thus far, but DH is looking into sraying now with copper fungicide. Any thoughts on that?

Thanks again!

    Bookmark   May 31, 2007 at 11:31AM
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billv(z6 WVA)

Sorry to tell you this but I think the key to surviving Black Rot is to spray with an effective fungicide early - shoots 1/2" to 3/4" - and every week to 10 days until withdrawal time hits about 9 weeks before harvest. Of several effective fungicides, the only one I have been able to purchase is Mancozeb (not Pristine, Bayleton, Abound, Sovran, etc.). Captan also is listed as effective by some and more commonly available. Good Luck.

    Bookmark   May 31, 2007 at 12:14PM
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fruitnut Z7 4500ft SW TX

Unfortunately Ruby and Thompson are poorly adapted to humid conditions. They are intended for areas with very dry summers like CA. I'm surprised they look as good as they do. Not sure what to make of the leaf curling. You really would be better served by cultivars bred in Arkansas such as Reliance and Jupiter.

The Fruitnut

    Bookmark   May 31, 2007 at 3:42PM
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Scott F Smith(6B/7A MD)

BourbonLady, some good advice given by Bill & Fruitnut. I use copper myself for black rot - if you are an organic grower like me it is the only option. It is also one of the best available for home growers, it is nearly as good as Mancozeb I would say. I am also experimenting with Yucca extract which has recently been shown to help. I have had almost zero black rot in my vineyard with a regular spray program. You need to hit particularly hard during May-June (now), that is when the diseases really take hold.

Scott

    Bookmark   May 31, 2007 at 4:31PM
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billv(z6 WVA)

Scott:
I have not tried copper but if you find it nearly as good as Mancozeb, I definitely will. Thanks.
Bill

    Bookmark   June 1, 2007 at 8:29AM
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Scott F Smith(6B/7A MD)

Bill, I always use a sticker with copper and that could be a reason it is so effective for me. Right now I am using both Nufilm-17 and Yucca extract as stickers. Its takes a long, hard rain to wash the copper off when it is put on with a tenacious sticker. I also spray the undersides of the leaves very thoroughly because the rain will not wash that spray off as easily. Also it is my impression that both black rot and downy attack the underside of the leaf first. Those two account for all of my major disease issues here.

The disease pressure this spring has been the least I can remember, thanks to the record dry spell we are having. I read in the paper this morning that May was the fourth-dryest on record.

Scott

    Bookmark   June 1, 2007 at 9:08AM
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