In my experience, not very. I can't say whether it's better than nothing as I have not done any careful comparison. But it's never done more than slow (at best) the spread for me.

It would be better to alternate between different products. Actinovate would be one and Regalia would be another. Ami

I used it year before last and was not impressed. I have had better results from Daconil, corn meal soak spray, potassium bicarbonate, Actinovate, and 1/2 strength (1.5% hydrogen peroxide) sprayed on at dusk. Not all of above mixed!!!
Use a different spray material every couple weeks. Don't mix
other materials with the hydrogen peroxide!

I assume Actinovate is also organic and can be used on vegetables? How do you make corn meal soak spray?

I guess another question is how long I can hold off early blight so that I get a decent production out of my tomato plants. Right now there are only a couple of yellow dead leaves. All the other blight leaves I pulled off had just 1 tiny little dot of blight. I assume those will grow into larger circles if I hadn't pulled them off. My tomatoes are setting fruits but they just started doing that. I feel very torn between organic and the chemical solutions. I think I can live with a lower production as long as it isn't more than 30% lower.

I've used Serenade, and Daconil in the past, and serenade is effective, but requires frequent spraying - Daconil does as well, but I feel you need to apply Serenade more often to get the same efficacy.

That being said, it does seem to work if used often enough and I prefer it to Daconil since I prefer to stay organic. I'm not a commercial farmer trying to scrape every last penny out of my harvest, I just want to get a decent harvest of organically grown tomatoes. I don't need perfect plants, just want to help them along a little.

I may try Actinovate next since I've heard good things about it, but I currently don't have a local source for it.

homegardenpa, yeah that is how I feel about Daconil as well. I know it works but I just can't bring myself to using it. I am willing to take some loss to stay organic. I bought Actinovate online from Amazon, so it will be here next week. I will alternate that with Serenade. How often do you spray Serenade?

You can get Actinovate from Amazon.

And the price has dropped now, too.

Cindy

Here is a link that might be useful: Amazon

I've used Serenade and found it effective. I have not tried
Daconil as the Serenade worked well enough for me (except
last year against LATE blight). I do agree that you
probably have to spray more often but you should be using
a spreader-sticker to reduce that requirement. I sometimes
alternate with copper soap and my crop is normally fine.

By the way, you can get Serenade much less expensively if
you buy it in a larger quantity from the manufacturer's
rep. I don't remember who that is and am not repeating the
research just for this post. If there is a lot of interest,
I'll see what I can find out. Last year, I bought a 7 lb.
bag for $70, free shipping. That's so much that I gave
away a few pounds here on the forum. Compare that with
Gardens Alive, where they get about $50 a pound. Also,
Serenade can be stored and will last, according to the rep,
for years. I sealed it in clean peanut butter jars and
put it in a dark cabinet.

I use about two teaspoonsful of powder in a gallon of
water. The bag come with instructions for a large area
(per acre) but smaller areas can be figured from that.
You really don't need much.

sneezer2, what is a spreader-sticker? I plan to spray once a week and more often if the weather is wet. Sure hope it is enough.

Spreader-sticker is a material you mix in with the spray. It
will be called just that though it may be of various brands.
It consists of a surfactant to aid the solution in wetting
the leaves (spreader) and a resin to keep the active
ingredient there longer. A "good" garden store "should"
have it but few do. Farm suppliers mostly have it and you
migjht find some on the internet. Bonide makes one.

Would anything like baking soda or other household ingredient serve the purpose of spreader-sticker? I will check the local garden store to see if they have any.

Do you think baking soda has any surfactants or resins in it?

Spreader stickers are usually petroleum based. They make sprays cling to leaves instead of run off leaves. Think of watering cole crops like broc & cauli & how the water beads & rolls right off the leaves. Spreader stickers are supposed to prevent this, in theory at least.

Could neem oil be used as a spreader-sticker?

Priscilia,.. I don't know what " spreader-sticker" is but:
Neem Oil spray is both a fungicide and pesticide.
It is Organic equivalent of Daconil as fungus prevention and it also repels some insects.

Sey