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San Jose

My PM problem was bad last year, so I'm sure it is in my
patch soil. How do I get rid of it? Assuming a fungicide is
needed, does that adversely affect my soil for next season?

11/10/2023 6:42:05 PM

San Diego, CA

Following this thread.

I had a terrible case this year myself on ALL my tomato plants, was actually debilitating. Started last season. Tried rotating many organic foliar applications including milk, baking soda, cold-pressed neem oil and copper. All worked to some extent, but the PM always returned and returned with a vengeance. I'm convinced it's in the soil, always lurking.

Now experimenting w/ Potassium Bicarbonate foliar applications thanks to advice from a few veteran growers.

I've read/heard about an amazing synthetic fungicide that will eliminate PM, but I still want to eat my tomatoes after putting in all the effort.

11/11/2023 8:52:15 PM

here is an article that agrees with your advice

https://www.weekand.com/home-garden/article/kill-powdery-mildew-spores-soil-18017878.php

11/11/2023 9:24:44 PM

Bethlehem CT

I have always been taught that powdery mildew was primarily an airborne disease and not generally transmitted from the soil. Powdery mildew is an obligate parasite and most often requires a living host to spread from. I know you are in a mild climate much different than mine so I wanted to be sure before commenting on this thread. I did find some information from the University of California that mentions, typically in California the powdery is coming from weeds that are the hosts. once in the air it can travel great distances. For us in the Northeast it generally takes a few months for pm to blow in from the south. ALthough that has been changing as of late with many more greenhouse's growing year around and also bedding plants being shipped great distances, many airborne diseases are showing up earlier and earlier around here.

Here is the link from UCal
https://ipm.ucanr.edu/agriculture/cucurbits/powdery-mildew/#:~:text=Powdery%20mildew%20of%20cucurbits%20may,of%20each%20fungus%20also%20exist.

11/14/2023 1:43:52 PM

San Jose

Thanks Moon, I believe my PM comes from my neighbor's zucchini patch-he doesn't believe in PM control and by
mid-August his plants look like they're covered with snow,
then the wind blows it on over to my patch.

11/14/2023 6:58:11 PM

Syracuse, NY

PM is like a global variable and will affect a great area, and my information here is that I had PM on plants that were directly across from a field of last-year's residue, (then corn) where the wind always comes from and NONE on plants that were over the river and through the woods...whoops, too early;
...err, on the other side of a gentle incline that simply goes a few hundred feet 'out back' and over a mild hill downward where wind damage is non-existent and I'm seeing that physical barriers can play a role in prevention and/or mitigation of it. I had thought and still do as Moon has said about a source, having not considered other temperate zones than mine alone. The worst PM was on a FP plant up against the back of my house, where nothing has ever been planted prior and wind is minimal. Back to Square One 4 me. Oh, and I prefer Joel Holland's Mildew Cure, as I believe the PM here in CNY is killed by the cold, else I'd have it on my fresh plant-outs. Oh, No! eg

11/15/2023 1:31:14 AM

Bethlehem CT

Shade plays a factor too. I had one of my plants get it worse than the other this year. They were right next to eachother, the only difference was one was in more shade.

11/15/2023 7:41:37 AM

Syracuse, NY

...and which one had more PM, Mister, lol? eg

11/15/2023 10:43:49 AM

Bethlehem CT

the shaded side

11/16/2023 7:08:24 AM

Brooklyn Corner, Nova Scotia

PM is becoming more troublesome each year it seems. This year I used neem oil for the first time on two plants and I didn’t see any evidence of PM right until first frost. A third plant, growing ornamental pumpkins about 20 feet away from the other two became affected, slowly at first then quite heavily.

I will be using it again for sure as it’s anti- bacterial properties which is a problem for me.

11/16/2023 8:35:16 AM

San Diego, CA

Checking back to review new comments. Thanks to those that have contributed, it's much appreciated.

Quick update on my experimental usage of Potassium Bicarbonate to combat PM.... the spread appears to have slowed, but it did not cure/eliminate the existing infection on the lower leaves and stem. I have some new seedlings nearby that I've been treating with alternate weekly applications of Neem and K-bicarbonate since they've sprouted. Will see if early and often treatment (pre-infection) helps prevent infection of PM before it takes hold.

11/16/2023 12:18:56 PM

Commack, NY

How much potassium bicarbonate are you using per gallon? I found that it had a tendency to burn my plants in amounts greater than 1/2 tsp per gallon when mixed with JMS stylet oil.

11/26/2023 7:52:59 AM