grapes--what makes them fall off when they are tiny?

[greybeard]

3rd year with this grape vine--1st year it just grew. Last year, about a dozen bunches formed but most of the tiny grapes disappeared when they were about 1/2 the size of a BB--I blamed it on birds--got just a handful of mature grapes from it.
This year (it's been wet) I covered the whole thing with mesh and there are hundreds of bunches on it, but again, most of them are disappearing while they are about the size of a pin head, leaving just bunches of stems. Is there something that causes the fruit not to 'set' and stay put? We did have a heavy rain last week and a lot of wind but I can't imagine big vineyards would have to cover their whole place to keep the little grapes from just blowing off the first time a breeze comes along.
(I don't remember the variety, but supposed to be a table grape--an eating grape, not a wine grape.

 

[Rafter S]

I won't pretend to know anything about grapes, but I do know that flowers have to be pollinated to set fruit. Is it possible that isn't happening? Again, I don't know about grapes, but some fruit trees are self-pollinating while others need a pollinator.

 

[Bigfoot]

I have limited experience with grapes, and have t raised any since 2006. A wet year will do that to them. Don't know if the rain beats them off, or if the moisture promotes a fungus. I know the only way to have many grapes is to prune the vine pretty severely. Like about as much vine on the ground when your done, as left on the fence. Seems like if peaches do good, it's the same year grapes do good here.

 

[Jogeephus]

I asked an expert this question today and after an hour and a half I'm afraid I have a heck of a headache and don't have an answer for you. I tried. He said it could be a host of things and he needed to know the variety of grape to tell you what it could be. But reading between the lines I would think with your rain and weather it would be a fungus. He mentioned fruit rot or botrytis bunch rot - also bitter rot(?). Some grapes have this problem some don't. If yours are susceptible then you need to spray with fungicide at least twice as it begins to bloom. He mentioned a lot more stuff too but I was in sensory overload and went to eating crayons so I don't remember much other than I liked the red crayons the best.

 

[TexasBred]

This didn't come from the folks that make the MD-2020 so take it with a grain of salt:

Black Rot
Black rot is the most destructive grape disease in Georgia. Therefore, the entire cultural program should be pointed toward its control. Other diseases will be less troublesome when recommended practices for black rot control are carried out. Understanding this disease will enable you to produce greater yields of high-quality grapes.

Source of infection: The fungus overwinters in infected canes and grapes, spreading to new growth early in the spring as green tissue appears and suitable weather conditions develop.

After the disease becomes established in new shoots, leaves, tendrils and blooms, the fungus reproduces in great quantity and spreads rapidly in recurring waves during each rain. Grapes become infected by the time they are fully grown, dry and shatter to the ground. There they remain as a source of disease the following year.

Symptoms: The black rot fungus attacks all parts of the grape vine. Leaf infection appears as tiny, reddish-brown spots on the upper surface in early June. The lesions enlarge to one-forth inch or more in diameter and become brown with black borders. A ring of black fungus bodies develops near the outer edge of the brown area. Lesions on stems and tendrils are longer and blacker than those on leaves. Stem lesions are narrow, sunken and often split lengthwise on the vine.

Infections begin to appear on the fruit when the grapes are about half grown. At first, a small, white spot forms. It enlarges rapidly until the entire grape is rotten. Affected grapes soon turn black, shrivel and dry up. Minute, black fungus fruiting bodies develop on the surface of the dried fruit.

The other site ascribes grape shatter to the weather/growing conditions:
http://carolyntillie_ultimate_californi ... nally.html

To demonstrate the damage that the rains have caused, I shot a picture of these grapes down on the valley floor (I won't say where, exactly). It is both an excellent illustration on just how far along the grapes are coming just 1,500 feet below us, but it also shows how bad shatter is. Grape shatter is where a major portion of the cluster fail to develop during its infancy. Damage to the blossoms prevent the grape from ever forming and in the case of this season, the rains damaged the flowers and early formation so that the grapes simply never had the capability of maturing.

This website has a good presentation and lots of pictures of fungal diseases and their prevention:
http://viticulture.hort.iastate.edu/inf ... mgmt03.pdf

 

[Jogeephus]

TB, I think he mentioned the shatter while I was eating the green crayons.

If it were my vines, I'd spray them with an insecticide and a fungicide in the spring. One of these treatments ought to fix the problem whatever it is.

Edit: My head's gone back to hurting again just by revisiting this thread. Maybe next time I'll insist on organic crayons.

 

[greybeard]

I tend to think at least part of it was the rain and wind------noticed this morning, that the clusters that are down under the bulk of the foliage fared better than any of the more exposed bunches.

 

[Jogeephus]

May well be but what about last years crop you lost?

 

[greybeard]

Well, I don't remember what the weather was like last year--can barely remember last month, but I don't like spraying anything with insecticide once the fruit starts forming , and it already has.
Besides, I'm no longer sure whether to use real surfactant or Palmolvive dish soap and I just don't need no more stress in my life. :hide:

 

[Jogeephus]

There are some grapes that have to be sprayed with a fungicide else they will not bear. Fungicides are typically a copper solution so its not like you are putting poison on the fruit. If you can figure out or remember what the grape is I can get you a lot of specific growing information.

 

[greybeard]

It's been too long ago Joe to remember what variety I bought--I just bought them on a whim at the Co-op when I picked up feed and herbicide and saw them in the garden area. They start off green and when mature are a purple, but I know they weren't regular Concord. Did get a handfull or two off the vine last year and they were sweet.
I have at least one kind of fungicide but I got it for my roses and it's (I loathe to use the word lest SL pop in here) sulfur based :hide: and even tho it does have a picture of roses, lettuce, strawberries, and grape bunches on the front, it also carries a warning that some varieties of grapes (specifically Concord types) can be damaged by sulfur compounds. I'll have to look on my shelf and see if I have any copper based fungicide.

 

[Jogeephus]

The guy right down the road from me is an expert in vineyards and winemaking and he can near about answer anything on this subject but its best to have a very concise question else you'll be eating crayons and wishing you was somewhere else.

 

[greybeard]

I've come to the conclusion that at least part of my problem is "Zed--we have a bug". I see lots of leaves with holes eaten in them now.
Found 2-3 white furry worms (look like what I call an Asp) on both my grape vine and my scuppernong vine--scuppernong is on the other side of the yard. Also found some curled leaves, and when unfurled, found the leaf held together by web looking material, and a couple little green worms about 3/4" long. I have some liquid Sevin, I'll have to read up on applying it to producing grape vines--still looking for a copper based fungicide--everything I find here is sulfur based and has a warning about using it on Concord influenced vines.

 

[Jogeephus]

Any fungicide should work You can buy it online here.

http://www.starkbros.com/products/tools ... aQodrI4AiA

If ya'll grow pecans in your area copper sulfate should be at the coop.

 

[greybeard]

I finally found some copper fungicide, and will use it when the weather clears, and after I treat for another problem.
I have a new problem with my grapevines. 99% sure it is Desmia funeralis grape leafolder. Little tiny worms no more than 3/4" long and about as big in diameter as a grain of rice. When you unroll the leaves, that critter wiggles like hack, so I have been just going along, looking for the rolled up leaves, and squashing the critter inside the leaf while it's still rolled up.
I have both liquid sevin and BT here--fruit still a month away from harvest, especially my scuppernong. I think I will try the sevin first.
This describes my pest to a tee:
http://entnemdept.ufl.edu/creatures/fru ... folder.htm

 

[MudHog]

greybeard, have you had much luck with Grapes at all? Pierce's Disease is s big problem in the South and why you don't see many vineyards in the South. Here is some reading up on PD and Grapes.

http://aggie-horticulture.tamu.edu/frui ... grapes.pdf

 

[glennst1011]

Any update on this. I am having the exact same problem. I have green grape and I too forgot the name. I am in North Houston area and bought the grapes at Walmart which likely was not a smart move. Beautiful bunches, loaded with pin head size grapes, then they all start disappearing leaving a empty vine bundle skeleton that eventually shrivels. Leaves look good, no insects seen, so I am curious if birds are stripping them?

 

[Redgully]

Not sure if you get downy mildew there but is a bugger. Spray with phosphonic acid. If you're looking for a silver bullet use ridomil. For caterpillars use dipel, an organic bacteria that overwhelms the gut of the caterpillar. We are not organic but use heaps of it and really works.

 

[Travlr]

Well, I don't remember what the weather was like last year--can barely remember last month, but I don't like spraying anything with insecticide once the fruit starts forming , and it already has.
Besides, I'm no longer sure whether to use real surfactant or Palmolvive dish soap and I just don't need no more stress in my life. :hide:

I don't know grapes at all, but I like Bigfoot's suggestion to prune the vine thoroughly. I know there are other plants that do better once pruned.

Probably best pruned in the fall after the first heavy frost.

 

[BelleCordes]

Fruit drop is usually caused by either fungal infection, insect damage, drought or lacking some nutrient in the soil. If you don't see any sign of disease or pests and you're watering sufficiently, maybe consider having your soil tested? Also, this being a cattle forum, is there any chance you are putting too much fertilizer on them? Too much nitrogen will cause them to drop fruit in favor of producing more green. You'll have beautiful vines with no fruit. Before you start dumping chemicals on them, consider getting a soil test. Look up recommended levels of calcium, phosphorus, magnesium, nitrogen for grapes and adjust what's missing.
Also, biologic spray for fungus (like CEASE) can be used up to the day you pick fruit. Copper should only be used before bud break.