Last year I had tons of grape clusters for the 1st time and suddenly they started to rot/turning brown and lost all the grapes. I think it is fungal disease. At the moment clusters are forming but they have not opened yet. Can anyone suggest an organic spray and when I should do this, thx in advance
Black rot is hard to control organically. You need to do 4-5 copper sprays to control it, starting with delayed dormant, then do 1" shoots then 1’ shoots and then every 2-3 weeks. After doing that for ten years I gave up on organic and switched to one myclobutanil spray at around 1’ shoots - its more effective than all that copper and is better for the environment as well.
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Copper and Sulfur are both organic, but you sure wouldn’t want to eat them!!! I use Manzate/Mancozeb and Sulfur until about 66 days before harvest and then switch to Captan and Sulfur. I start spraying as soon as the first leaves form and keep it up until around the 4th of July, after that, the grapes are not susceptible to disease. You have to spray before the diseases start as the sprays are preventative. Once the vines are diseased, it’s too late and the sprays won’t be effective.
The most critical time to spray is from bloom until about a month later (actually, I’m not really sure how long the critical period is, but it starts at bloom).
Here’s a spray guide for Virginia, but it will work anywhere.
Page 11 is where they give info on what to spray and when to spray.
All the vines have leafed out and I see blossom clusters but they have not opened. I have copper spray. do I just spray the leaves or should I spray the blossom clusters too. Is it too late to spray now? Myclobutani is not organic? thx
OK thx for info Bart. So I can still spray when the flower clusters open? thx
Yes you can spray flower clusters. Copper is organic but is harmful to soil organisms. Sulphur is relatively benign but does not help at all with black rot. Myclobutanil and the other sprays Bart mentions are not organic.
thx Scott. Is Myclobutani toxic to bees and such? I cant remember but I read somewhere that says use Baking soda?
I spray everything! It’s (hopefully) not too late to start spraying.
I’m growing wine grapes which I believe are harder to grow/more susceptible to rots and mildews than table grapes, so I spray like crazy. A lot of your problems (or non-problems) are related to where you are. In the hot and humid mid-Atlantic, a heavy duty spray program is a requirement, but out in dry California, I think you can get away with a lot less spraying.
Myclobutanil is not known to be toxic to bees. Baking soda helps with powdery mildew but thats about it.
I hope you are not growing vinifera grapes, they are a pain in the east even with lots of synthetic sprays. I have hybrid grapes and muscadines only and the one spray per year program works on them.
I am in zone 6. The variety I have Neptune ,Tickled Pink, Catawba and Reliance(I think) It has been very wet here recently! thx
I tried muscadine but it went kaput on me. Never heard of vinifera. ,I have Neptune Tickled Pink Catawba and I think Reliance. Does sulfur come in a spray? May try baking soda. Just add water to baking soda? what is the water to soda ratio? I am concern about Myclobutani, so I prob wont use it and will kick myself at the end of the season! Thx
vinifera is pure non-american grapes, most of the ones in the stores and grown in California are vinifera. I think all yours are hybrids.
Sulphur comes in a spray, e.g. Bonide liquid sulphur. If you are not getting powdery mildew there is no reason to spray any baking soda as that is all it helps with. If you have black rot only copper will do anything. I spent five years trying various things and suffered a lot.
Here is a sheet with more info on organic grape growing in a humid climate:
https://www.oardc.ohio-state.edu/fruitpathology/organic/PDF/OSU-Organic-Grape-Diseases.pdf
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Vinifera is the species name for wine grapes. Chardonnay, Cabernet Sauvignon, Merlot, etc are all Vitis vinifera grapes.
Its not exactly wine grapes, its the European / Middle Eastern species. Most store table grapes are pure vinifera (Thompson Seedless, etc) and there are also many wine grapes that are not pure vinfera, e.g. Chambourcin, Cayuga, etc.
OK. thx Scott. I will read through. Yes it gets humid where I am 
Copper and Sulfate can meet the standards for Organic depending how they are chelated. For example copper lignosulfate does meet requirements but many common off-the-shelf copper products do not.
Thanks for the correction Scott!
Actually a fair number of them (at least sold out here) have a bit of Canadian geneology.