Organic Grape Sprays?

silent88April 25, 2014

Hi everyone,

Last year a lot of my grape clusters got black fungus and mildew on them and so I did not get very many good grapes. I am relatively new to this, and last year was really my first harvest. This year, I have quite a bit of clusters for red flame and some thompson seedless grapes and some are beginning to "blossom." I have heard that you need to spray the actual clusters with a fungicide to prevent fungus later on. Since I will be eating the grapes, I do not know what is safe to spray them with. I do not want to poison myself. However, I know how toxic fungal spores can be to injects, so I'm wondering what/if I should spray with that is safe for eating (eventually)? As a note, I usually practice completely organic gardening methods.

(I love on the coast of southern california so the weather is great for fungus).


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bart1(6/7 Northern VA)

I wouldn't get too hung up on "organic" if I were you. Once you see some of the things that qualify as organic you might get a different impression.

For instance when I first started, I was spaying copper and sulfur which are considered organic (at least I think they are), since they are just good old elements that exist on Earth. But you sure wouldn't want to sprinkle these powders on your cereal in the morning!

So my advice would be to spray the most effective thing you can get your hands on and can afford. (some of the commercial sprays are VERY expensive and only sold in quantites too large for a home grower).

Other things to consider are the timing of the sprays and the PHI (or pre-harvest interval).

You have to spray your grapes (or tomatoes or melons, etc) before you see signs of a problem. The spays are preventitive treatments. They stop mildews and rots from forming, but they don't do much of anything once the plant is infected.

Also, there's a certain point where the grapes themselves are no longer susceptible to rots and mildews so you can stop spraying them. For me in VA it's somewhere around the 4th of July. So for most of the summer and all the way up to harvest time, I don't need to spray my grapes. I still have to spray the leaves because they can still get infected, but you can avoid spraying the grapes themseleves.

Back to PHI - pre harvest interval - this tells you how much time you need between your last spraying and your harvest to be safe. Some sprays like manzate/mancozeb have very long PHIs (66 days for that one I think), and some have much shorter PHIs. So what you end up doing is spraying with different things at different points in the season.

You will also probably have to combine sprays since certain problems can only be treated with certain sprays, but you can do it in the same sprayer so it's not really a big deal. When you look at the spray guides they say something like "Spray with XXXX and one of the following" YYY, or ZZZ, or AAAA, or BBBB"

It probably all sounds very confusing and overwhelming and it sort of is. But once you start reading the spray guides and asking more questions in here, it will become easier and more clear.

Below is a link to a Mid-Western spray guide to get you started.

Here is a link that might be useful: Purdue Spray Guide

    Bookmark   April 25, 2014 at 8:47AM
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Let me get all this straight,,,

So, these fungicides are safe for human consumption if you wait until after the PHI? Do they just break down or wash away by that time period or what? It all seems so complicated! Basically just look for a food safe fungicide and go for it? As long as I wait for the PHI period to pass I'm fine?

I'm still afraid to spray stuff I wouldn't eat. I'm afraid to screw up and poison myself or my family.... I wonder if grapes can go without any spray?

How do you know when they don't need spraying anymore? Some of my flowers are actually tiny grapes at this point.

    Bookmark   April 25, 2014 at 10:26AM
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Scott F Smith(6B/7A MD)

Copper and sulphur are not safe for human consumption in large quantities, but by the time you harvest there should be so little left as to be in the noise. The same holds for the synthetic fungicides. The main advantage of the organic products is they were already in the environment so are less toxic to fish etc since they are used to them in small quantities already.

My recommendation is you start with summer oil (edible), switch to sulphur if that is not working, and then consider synthetics such as myclobutanil if that is not working. You also should consider growing hybrid grapes which are much more disease resistant. I wouldn't even consider growing your varieties where I am located.


    Bookmark   April 25, 2014 at 10:46AM
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Austin. I share your concern. This is my first year attempting the organic approach. My one and only grape (Mars) had fungus issues last year. I'm trying Serenade (Amazon) this year. It is listed as organic. I originally bought it for fireblight and rust prevention for my apple and pear trees. Not sure it will do but so far so good. Best wishes, Bill

    Bookmark   April 25, 2014 at 11:26AM
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bart1(6/7 Northern VA)

So, these fungicides are safe for human consumption if you wait until after the PHI? Do they just break down or wash away by that time period or what?

That's basically it. Rain, sun, dew, wind, time all break down the sprays. That's also the reason you have to keep spraying which we haven't covered yet! I spray every 2 weeks but probably should do it every 10 days but I just don't have the time during the week.

You also need to start spraying early. The most important time is between flowering and grape formation so for you that's now(!) and a couple of weeks ago(!!!)

Check out the spray guide I linked to starting on p15. My only concern about downy and powery mildew, black rot and phomopsis. I don't spray for bugs on the grape vines.

The other thing to think about is all the fruit you've eaten. Unless it's truly organic, it's proabbly sprayed with a lot more nasty stuff than you'll ever use! ;-) Especially if it's coming from outside the US.

When it comes time to harvest, pay attention to the PHI and add more time to it if it makes you feel better and then wash the hell out of them! And then wash them again.

But definately listen to what Scott says regarding growing organically. The only problem you and the rest of us face is by the time you figure out your current method is not working, the plants will be dead or infected and you'll have to wait unitl next year to try again.

    Bookmark   April 25, 2014 at 1:48PM
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Scott F Smith(6B/7A MD)

Bill, I have done a lot of Serenade spraying over the years. While I think its worthwhile to throw into the tank its weak stuff and may not keep your problems at bay. Sulphur is a clear notch better for most diseases.

My current grape regimen is one myclobutanil spray at about 6" shoots, and a couple sprays of sulphur and/or Serenade at various other points. Without the myclobutanil I get black rot in a bad way, sulphur and Serenade are not effective against it (both in my orchard and in all the studies). Copper is the one effective control that is organic, but I view myclobutanil as similar environmental impact overall since copper is bad for soil health if too much is sprayed over the years.

For the original poster, they are in California and black rot is not a problem so its much easier to grow grapes organically.


    Bookmark   April 25, 2014 at 5:44PM
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Thanks for the advice, everyone. I may try the sulfur sprays then for now. If that does not work I will try some synthetic next year. I have a copper dormant spray. What is summer oil? I know the market grapes (I try only to buy from the US though) are probably loaded with chemicals. However, they are trained and have to follow regulations, and I could easily mess up and spray too much or eat them too soon. Don't the fungicides absorb into the grape themselves when you spray?

And the jist I get from some of you is to grow resistant varieties etc.... Does this mean you don't spray? I didn't do much research when I planted these 4 years ago.

And to be clear I don't need to spray yet it is just preventative for my grape clusters. The past few years I have not sprayed the plant at all. The leaves and shoots tend to do fine. Toward the end of the season they have a little bit of mildew stuff or black spots but then I just prune it out when they go dormant.

Oh and my post is confusing but, what I intend to do since I have birds that would love to eat all my grapes, is cover them with paper bags. It helped last year but may have contributed to fungus. But if I don't do it the birds eat them all. Since the fungicide is supposed to wash off/blow off, etc, will that be bad?

    Bookmark   April 25, 2014 at 9:03PM
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