lehua:

Your Thompson is infected with powdery mildew. You will have to spray or dust sulfur or one of the systemic fungicides. This is the most widespread disease of grapes in CA. You need to start spraying early in the season. Spraying now will help but there will still be damage to the fruit. Sorry but if you don't want to spray you might as well rip your grapes out.

The Fruitnut

I have the same thing on my thompson. Will it infect my Perlette that is across the yard?

tim:

Most California grape varieties are suseptible. Some more than others. The breeders are working on resistant varieties but all now aval probably need spraying.

The Fruitnut

Mahalo Fruitnut,

You are not so nuts after all. Anyone know the best method of spraying or brand of spray that kills powdery mildew. How would you apply a systemic. On the leaves directly or soaked in to the roots? Recommendations please.

Aloha

Aloha:

Commercial grape growers mostly use dusting sulfur. But that is primarily a cost issue. It is kinda nasty to apply and can damage the foliage under some conditions. I used to use wettable sulfur sprayed on other crops for powdery mildew. That would probably work here. When I was in CA I used Bayleton sprayed on the foliage and fruit. That is a systemic. I think there are more systemics but you would need to ask a knowledgeable sales person or someone else.

You might Google: grape powdery mildew control fungicide systemic.

The Fruitnut

I know very little about grapes other than the wild one which grows here on my property (and we eat them). But, for me, I've got a bad case of Powdery Mildew over here in Rhode Island, on multiple types of plants. Worst hit are some of my DR apple tress which are supposedly very resistant to PM. *sigh* I already gave them a sulfur treatment earlier in the season, but I'm not sure how much it helped. I thought sulfur was more of a protectant rather than an irradicant? Anyway, I decided to get tough and order systemic Immunox to see how that will work. I had wanted to experiment with Immunox anyway to see how it compared against Ferbam for Cedar Apple Rust next year. I had to order it online, as I couldnÂt find it at my 7 local nurseries. DonÂt be confused with "Immunox Plus" which is more widely available, but also has an insecticide which isnÂt rated for fruit. According to this link, it's very effective against PM for my apples:

http://www.caf.wvu.edu/kearneysville/vadisbul.pdf

According to this pesticide page, it is rated for grapes as a foliar treatment So, IÂm not sure what it means when you already have grapes:

http://www.pesticideinfo.org/Detail_Product.jsp?REG_NR=00968800123&DIST_NR=008845

According to this link, others are using it for grapes, and itÂs among their last seasonal sprays:

http://www.jackeden.com/cgi-bin/sheets/viewdata.cgi?id=1144209836

HereÂs the product homepage:
http://www.spectracide.com/ProductCategories/RoseAndFlowerCare/SpectracideImmunox/

Note: I only ordered this yesterday, so I don't yet know the results of how effective it will be for me.

Again, to quote another poster, I know very little, but I did stay at a Holiday Inn Express last night. Please double check all my info before acting on it.

Other thoughts/opinions are welcome.

-Glenn

Lehua, Thompson is problematic in the best climates, California for instance. There are lots of grapes that are more disease resistant than Thompson. Hawaii is a unique climate, to say the least. Your time would be best spent researching what varieties are already proven in Hawaii.

Thanks everyone,

I am on the attack. Gotta save my grapes.

Aloha.