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Old 06-11-2013, 02:48 PM
 
Location: SW MO
1,238 posts, read 4,267,733 times
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My grapevine (Thompson seedless) was doing very well, lots of grape clusters forming. We have had a very wet, cool spring and the clusters were just forming tiny grapes. About a week ago I noticed some brown clusters. Now, most of the clusters have turned brown, dried up and are falling off. What disease is this and how can I protect the few remaining grapes?
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Old 06-11-2013, 06:15 PM
 
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Are the brown clusters the grapes or the leaves? Grapes are very prone to fungal diseases. In fact, the discovery of the very first horticultural fungicide, Bordeaux powder, was during a disastrous year for the French grape crop centuries ago. The last Bordeaux powder was made and sold about 8-9 years ago and I bought a few packages of it for posterity, but there are many commercial fungicides that are used today. The trick is to apply them before the problemn rears its head. We are not that far from you, so I know what kind of spring you've had -- snow in May and everything!

Here is an article from MU Extension, and I think it might address your problem. Good luck.
Black Rot of Grapes
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Old 06-11-2013, 07:08 PM
 
Location: SW MO
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It is the actual grape clusters that are falling off. I have used a fungicide before for black spot on the actual grapes, but never had a problem with the undeveloped clusters. Last summer was hot and dry, I had a bumper crop. This year isn't going to turn out so well.
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Old 06-11-2013, 07:36 PM
 
Location: East of Seattle since 1992, originally from SF Bay Area
38,234 posts, read 68,927,881 times
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That sounds like they just didn't get pollinated. They don't need bees but the breeze and just the falling of the pollen does it, but if it's raining, or have a cold wind during that time you will can lose them.
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Old 06-16-2013, 11:08 AM
 
Location: North Idaho
29,152 posts, read 39,994,391 times
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Wet cool weather, I would suspect a mildew disease. I suggest that you get the appropriate spray and start treating. I use Immunox. Follow label directions.

In areas with lots of rain, grapes should be pruned really hard so that the plant is well opened to air flow. In fact, you can prune grapes in the summer to open them up a bit.
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Old 06-16-2013, 08:55 PM
 
Location: Charlotte, NC dreaming of other places
983 posts, read 2,386,159 times
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I just noticed the same thing on my grapevine. The tiny clusters are not developing and some are drying out. We had a ton of rain here in NC and we have more coming. This is the first year I see grapes on my vine and I m really disappointed that it's not doing well.
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Old 06-16-2015, 07:42 AM
 
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Default Is it too late to pollinate???

My grapes are also turning bronw and falling off.... is it too late to pollinate??? Will they all fall off?
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Old 06-16-2015, 07:58 AM
 
Location: East of Seattle since 1992, originally from SF Bay Area
38,234 posts, read 68,927,881 times
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The pollination must happen when they are in flower, after that it's too late (see pic below). This can also be caused by too much or not enough water.


https://foliageandflowers.wordpress..../grape-flower/
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