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Why did my grape vines th... #185371 - Ask Extension


Why did my grape vines th... #185371

Asked May 26, 2014, 1:33 PM EDT

Why did my grape vines that had all the little green grapes disappear and replaced with an empty cluster of just tiny fiber looking brittle stems ?.The birds did not eat them,I used netting also.Was it lack of minerals,poor soil or what?Last year vines produced fruit.Thank you.

Reno County Kansas

Expert Response

This problem sounds like poor pollination, but we would need more information to be sure. Normally a certain percentage of the flowers on a cluster fail to pollinate and fall off about a week after bloom. We call that "Shatter". If cool, wet weather occurred during pollination, there may have been a total failure of pollination thus all the fruit fell off. Nutrition can also play a role, especially deficiency of boron or zinc. There are also some insects, especially rose chafer, that feed on the developing flowers and cause poor fruit set. Again, we would need more information to know for sure.
Bruce Bordelon Replied May 28, 2014, 9:28 AM EDT
Thank you Bruce--I do not understand that if the grapes were already formed and in a cluster--how could pollination be a reason?Also what % of boron and zinc per vine is recommended.Thank you.DJM Hutchinson,Ks.
The Question Asker Replied May 28, 2014, 10:45 AM EDT
Well...that's why I said I needed more information. How large were the berries when they fell off? Are you sure it was post-bloom? Unopened flowers look like small berries. If it was post fruit set, then I have not seen that problem before. Did your vines get exposed to 2,4-D herbicide through drift or volatility? 2,4-D is a common cause of poor fruit set if exposure happens before fruit set.

Our Midwest Grape Production Guide recommends 25-50 ppm Boron and 30-50 ppm zinc in petiole samples taken at veraison. See the guide for the full table.
Bruce Bordelon Replied May 28, 2014, 2:18 PM EDT

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