PM/fungus contradictory applications

[paradajky]

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!

[VirginiaClay]

You can't use sulfur and neem oil (or any other oil) within 14-21 days of each other. It causes leaf burn.

[paradajky]

Awesome, thank you!!

[KarenO]

When it comes to dealing with powdery mildew, the treatment approach is not very effective in general. Sulphur, neem, baking soda, milk etc all can provide some reasonable effectiveness in preventing or at least slowing down the development of the disease along with other good cultural practises like improving airflow, keeping foliage dry, where possible, etc. but none of them are very effective in my opinion to treat existing disease.
Resistant varieties and Preventative treatment will be the most effective approach when PM is going to be a yearly problem I think
KarenO

[paradajky]

Thanks, I'm starting early with preventative treatment this year, even though a couple seedlings already had shown some PM here and there. I should have good airflow in this area, and since my ground-garden is on drip system and my tomatoes are in a bucket/gutter system, foilage stays dry except for the daily coastal dew. Until june gloom is over.



I will look into PM resistant varieties for next season, thank you for the tip Hopefully there are some dwarf varieties!

[KarenO]

Another approach may be just to wait a bit longer to plant. If seedlings are not growing well and getting diseased early in the season it may be worth a try to either delay or stagger your plantings until the cool foggy time is over
My dwarfs seem to have done well in my cool spring nights
KarenO

[paradajky]

Interesting strategy. I might start a few from seed now just to see what happens, since it feels like our warm season has shifted forward a few months here in southern california (relatively speaking...). Hmmm.