Powdery mildew on grapes

A few bunches of my Pione vine might have this. Any good treatments? Prefer organic.

1 Like

I had powdery mildew on some of my muscadine grapes last year which caused the loss of maybe 25% of my harvest. It affected only the fruit and wasn’t visible anywhere else on the plants.

This year I have been using wettable sulfur (Bonide brand) as a spray to try and prevent this. So far it seems to be working. I believe it works more as a preventative than a treatment, so it may not help much in your situation. That being said, I have a small crape myrtle that had a bad case of powdery mildew this spring and a few treatments with the sulfur seems to have cleared it up.

Good luck!

I’ll have to track down what that is in Japan. Is another way to cure this for next year just to cut off the offending bunches and throw them away?

Looks like it’s spread to most of my grapes. Maybe because we’ve had an extremely wet summer. I’ll try to find some of this stuff. I assume it’s safe to eat just washing off the grape skin?

Sorry to hear that it has spread. The sulfur should keep it under control, though any fruit already infected will likely remain so.

The directions on the product I use says that it can be used up to the day of harvest, so washing the grapes before eating would be appropriate.

I’m surprised how well sulfur works on a variety of infected plants. Besides the grapes and crape myrtle I mentioned earlier, I have been using it on a large planting of zinnias that have been plagued with fungal issues in past years. With occasional sulfur applications this summer they have been disease free.


Get out at sunrise… find out for sure where first sunlight hits your grapevine… prune the canopy so that sunshine gets to your fruit for a couple hours at least early in the morning.

The sun rises in the east of course… if you can cut back the foliage on that side so that a few hours of morning sun gets to the fruit… that will help with moisture related issues.

Good luck



Thanks, well worth a try then.

That sounds like a great idea, I’ll see if I can do it. My trellis is permanently covered with clear frosted corrugated poly carbonate panels. It’s required in this area because of the amount of moisture we have. I over pruned last year, so most of the foliage is bunched together and poorly spaced.

Your post reminded me it I was time to do mine… my grapes are seedless concord… and my trellis runs due east and west.

I removed most of the canopy on the east and north sides. Left it all on the west and south side. Getting much better air flow now to the fruit and some morning sun… but protected from mid day and evening sun.

I think it would be more ideal if your grape trellis ran north/south. If so you could easily open up the east side to more morning sun.

Next time I start grapes or muscadine… I will keep that in mind.


1 Like

Ok guys, I’m at the shop now, and there’s many types of treatment. Apparently 2 are most popular. Not organic. If I’m reading the Japanese correctly, the active ingredients are:

Thyophinate methyl or

Are these safe to use?

There’s two organic treatments, but it looks like sodium bio carbonate or Basic copper chloride.

Any ideas?