PM/fungus contradictory applications

paradajky · June 1, 2023

Hi:

I read somewhere last year about contradictory applications when treating powdery mildew, and can't seem to find the information. I think it was something like don't use bleach or copper at least a week after using an oil-based treatment (e.g. neem or horticultural), or vice-versa. Spent a bit searching having trouble finding it again. Anyone know about this?

Background:
Here in coastal southern california it's been overcast and damp since mid april, with only a day or two of sunshine. We've even had some rain. Full on May Gray, now heading into June Gloom.

I got a late start on my tomato seeds just like last year, having sowed them about 6 weeks ago (mid-late April). They are outside and I've already pinched off a few leaves that had powdery mildew on them. I will be transplanting them to final growth spot this weekend. Squash okay so far. Something ate the cucumbers boooo. I sprayed the seedlings a few days ago with peroxide, it rained the next day, and I sprayed again with copper after the rains. Leaves look a little damaged but plants appear all right so far.

PM was one of the major diseases that took my tomatoes out last year after a very short harvest, despite good weather and weekly, alternating applications of 1.5% hydrogen peroxide and neem oil. For sure took out my cucumbers and squash, having only one short harvest. This year I'm trying copper and peroxide. I might put bleach in the rotation, or maybe consider the biofungicide method. I read through the entire bleach thread last year and maybe that's where I read about the contradictory application.

Thank you for your time!

June 1, 2023	#1
paradajky Tomatovillian™ Join Date: May 2021 Location: Coastal Southern CA Posts: 164	PM/fungus contradictory applications Hi: I read somewhere last year about contradictory applications when treating powdery mildew, and can't seem to find the information. I think it was something like don't use bleach or copper at least a week after using an oil-based treatment (e.g. neem or horticultural), or vice-versa. Spent a bit searching having trouble finding it again. Anyone know about this? Background: Here in coastal southern california it's been overcast and damp since mid april, with only a day or two of sunshine. We've even had some rain. Full on May Gray, now heading into June Gloom. I got a late start on my tomato seeds just like last year, having sowed them about 6 weeks ago (mid-late April). They are outside and I've already pinched off a few leaves that had powdery mildew on them. I will be transplanting them to final growth spot this weekend. Squash okay so far. Something ate the cucumbers boooo. I sprayed the seedlings a few days ago with peroxide, it rained the next day, and I sprayed again with copper after the rains. Leaves look a little damaged but plants appear all right so far. PM was one of the major diseases that took my tomatoes out last year after a very short harvest, despite good weather and weekly, alternating applications of 1.5% hydrogen peroxide and neem oil. For sure took out my cucumbers and squash, having only one short harvest. This year I'm trying copper and peroxide. I might put bleach in the rotation, or maybe consider the biofungicide method. I read through the entire bleach thread last year and maybe that's where I read about the contradictory application. Thank you for your time!