Grape problems

[Retired Guy]

Again this year our grape vines are having problems. In the late spring we see formation of grape clusters but as spring goes into summer the little grapes in the cluster start disappearing. Does anyone have the answer to this problem?

 

[begreen]

(broken link removed)

 

[1kzwoman]

I found this at the north Dakota extention website
Q: I have had grapevines for about 10 years. Until two years ago, they produced good crops. In recent years, I get adequate vine growth and many florets that begin to develop into grape clusters. However, when the grapes get to 1/8 inch in diameter, the grapes turn hard, black and do not develop into edible grapes. Last year, the vines produced minimal edible grapes. I added superphosphate to the root system, but it did not help. (e-mail reference)

A: It could be fruit rot or botrytis bunch rot. An on-site collection of the grapes and perhaps a lab culture will be needed to make a positive identification. Without knowing the pathogen, I would suggest starting a spray program using a bordeaux mixture as the plants begin to show new growth. Spray again on a two-week basis. I would encourage you to get an application on the grape clusters before they close to be sure the fungicide hits all sides of the individual grapes. This is a generic recommendation that should provide some protection. It’s like a doctor telling you to take “two aspirins,” hoping it will take care of the problem.

 

[HeatsTwice]

Again this year our grape vines are having problems. In the late spring we see formation of grape clusters but as spring goes into summer the little grapes in the cluster start disappearing. Does anyone have the answer to this problem?

Hi, may I humbly comment on this issue since I have a vineyard in the Napa California region and have been growing grapes/making wine for 13 years.

It looks to me that you have experienced "shatter". This is a phenomenon which occurs when the grapes are flowering. Since grapes are hermaphrodites, they mate with themselves and pretty much all of the clusters do it at the same time. A proper human analogy but maybe not appropriate here is how guys get morning wood. They all want it at the same time.

If, during this time there is rain, high or medium winds, or kids frolicking through your vines, this will knock the flowers/pollen sacks off the rachis (stem that the grapes attach to) and dramatically reduce the number of berries on each cluster - since each flower produces one grape berry.

That's what it looks like to me.

There is nothing you can do about it now, but next year prune later in the year. Pruning is your way of telling your vines to WAKE UP and get to work. Otherwise they will sleep until the weather gets warm and then harvest will be very late.

By pruning in April, instead of March, when the mass self-mating occurs, it's farther into the spring, and, with more winter behind them, are less vulnerable to wind & rain. Also you might want to tell the kids to stay outa the vineyard during this very private time for them.

 

[HeatsTwice]

I found this at the north Dakota extention website
Q: I have had grapevines for about 10 years. Until two years ago, they produced good crops. In recent years, I get adequate vine growth and many florets that begin to develop into grape clusters. However, when the grapes get to 1/8 inch in diameter, the grapes turn hard, black and do not develop into edible grapes. Last year, the vines produced minimal edible grapes. I added superphosphate to the root system, but it did not help. (e-mail reference)

A: It could be fruit rot or botrytis bunch rot. An on-site collection of the grapes and perhaps a lab culture will be needed to make a positive identification. Without knowing the pathogen, I would suggest starting a spray program using a bordeaux mixture as the plants begin to show new growth. Spray again on a two-week basis. I would encourage you to get an application on the grape clusters before they close to be sure the fungicide hits all sides of the individual grapes. This is a generic recommendation that should provide some protection. It’s like a doctor telling you to take “two aspirins,” hoping it will take care of the problem.

>It could be fruit rot or botrytis bunch rot.

I agree. Climate around the world seems to be changing. meaning that you will have to change your canopy management and then resort to spray with wet-able sulfur once every two weeks (if you sell your grapes and need the income - less frequently if you do not) - basically what you've already said.

As far as canopy management goes though, switch over to cane pruning. This has solve the rot problem for me - when combined with more frequent sulfur spraying. I used to have quadrilateral cordons which resulted with a very thick canopy which would not dry out from the morning dew over the day. This moisture fostered the same powdery mildew problems you are having. Cain pruning will reduce your cordons to only two young cains which allow ample air to circulate through the canopy and dry it out over the day.

Another trick is to do something called "leaf thinning": Pull the first three leaves off each cain on the south side of each row. This way morning sun will dry off the nigh/morning dew. Leaving the leaves on the north side of each row will keep the grapes from experiencing late afternoon sun burn. When morning dew is evaporate, the environment for mildew to grow is gone.

Leaf thinning also ads more aromatic flavors to the final wine from your grapes as more of the terrior of your vineyard is left in each grape, not flavors of localized atmospheric microclimate trapped in your canopy - which can give wine a musty, green pepper, quava flavor.

Oh, I forgot to say, I grow Savignion Blanc meaning that the crispness and fruity character of the wines made from my grapes are critical and only obtained from proper vineyard managment. If I don't leaf thin, I get a Savignion Blanc with guava and green peper over tones, If I do leaf thin, my Savignion Blanc has Apple, Citrus, and Melon over tones. Reds are a little more forgiving. Whites are hard to make.

 

[begreen]

Great information heatstwice. That was quite educational. I don't grow grapes but appreciate the art of growing them.

 

[BrotherBart]

Pains me to read these things. When we bought this place the drainfield beside the house just screamed to be set up for grapes. Crappy, rocky soil. Drainage. Sun. The whole shot. And I love me some wine. Never did it because every two to three years we would be going to move. None happened.

Fast forward 29 years and no grapes.

 

[Jags]

Good info. Northern IL is experiencing a resurgence of winerys. A couple of local ones are putting out some quality stuff.