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San Diego

Please take a look at my diary photos just posted and see if anyone can tell me what this is. Looks like powdery mildew, but it is unlike anything I have ever had in 15 years growing. Any help is really appreciated. thanks, Jim

8/14/2016 10:20:21 PM

Central NY

I vote pm...aggressive

8/15/2016 10:49:51 AM

Citrus Heights, CA

Jim, That's definitely powdery mildew. Unfortunately its probably to far advanced to control now,especially with organic methods. Ron Root

8/15/2016 9:38:07 PM

San Diego

My question is this: Why did this mildew react so different to years past and was spray resistant? I sprayed the plant when it had only 2 or 3 small round tiny spots on one leaf. Powdery mildew will be stopped or extremely slow to move when caught so early. This stuff spread like mayonnaise on white bread! It actually seemed like it spread faster after being sprayed. How can this be? Are there different kinds of pm?

8/16/2016 12:43:06 AM

Citrus Heights, CA

Jim, Powdery mildew is unfortunately a major problem for those of us who live in the milder climates of California. PM can over winter as spores or be actively growing on a number of host plants. Throw in all the home gardeners in summer equals lots of spores floating in the air. Being an organic grower, you are limited in your fight against PM. Most of the organic ways to combat PM are preventative at best so once present it will be hard to eradicate. Neem oil and some of the horticultural oils can eradicate mild to moderate PM sometimes. Yours looks as bad as I have seen in a giant pumpkin plant. I use to have problems with PM and was using daconil and eagle 20. Even using both of these the PM would continue spreading. I'm currently using even more chemical products along with daconil and eagle 20 in a rotation. I don't see PM in my patch anymore. While I'm not a disease expert I believe in our mild climate PM does become resistant to repeated products. Ron Root

8/16/2016 7:13:47 AM

San Diego

Thanks for the reply ron. I understand everything you are saying. I still ask, are there different kinds of pm? The look of this pm on our plant was different, the way it spread was different and it wiped off which was different. This strain of pm was like super powdery mildew or something i have never seen before.

8/16/2016 11:38:00 AM

Upa Creek, MO

Curious, but have you had more rain this year or humidity? Infection is worse the more humid the environment. I've had it so thick here where it looks like someone shredded up a cotton ball and spread across the leaf. The thicker it is, the more it looks to be brushing off, but spores are still there.

8/16/2016 12:54:38 PM

Citrus Heights, CA

Jim, Yes there are different types of powdery mildew. Podosphaera xanthii and Erysiphe cichoracearum are the two types that most commonly cause pumpkin PM. Of the two Podosphaera xanthii is the more aggressive one. There are other types out there. Dr. Margret Tuttle McGrath a plant pathologist specializing in powdery mildew gave a very good talk about PM at the pumpkin convention in Pennsylvania two years ago. She gave us a very good pamphlet on the subject. Jim you can google her name and a bunch of good info is available to read. Jim I wish you luck with your battle. Take care, Ron

8/16/2016 6:03:26 PM

Citrus Heights, CA

Luke, You bring up a good point about high humidity in your neck of the US. Where I grow we deal with very hot dry heat. The way I combat this heat is by running micro sprinklers from about 1030 in the AM to about 630 PM. I keep the plant constantly wet. when its over 105 I apply 2800 gallons of water daily. One unintended benefit of keeping the plants wet, is the spores of PM cannot attach to the leaf.

8/16/2016 6:17:56 PM

San Diego

Ron, thanks for all the info, we definitely got an aggressive type this year unfortunately. You learn every year even after a long time in this hobby.

8/17/2016 2:44:43 PM

Torrance, Ca.

Such a bummer Jim but the good thing is your boy will be happy with a 500 pound fruit! I'm sure he's had a ball growing this season!

8/17/2016 3:22:12 PM