Cercospora? Help me identify my leaf spots and treat them.

redraif(8)July 30, 2010

As the title states, I think I have Cercospora, or my hydrangeas do... lol... I have searched, but I want to be sure. Please can you help me id my spots so I can begin treating the problem. Thanks

Here is a bit of background in case its relevant before I post pics.

We have 9 young hydrangeas. I'm pretty sure they are all showing signs of this disease. I got them all from Home Depot. 6 were purchased 2 years ago and just transplanted. 3 were just bought this season. All are endless summer.

The 6 transplants were originally around a tree and were never able to transition to the environment. Not sure if they got too much sun or just had too much competition from the tree roots for water. They were always wilty and small. We prepped a bed just for them this year with eastern morning light instead of the harsh afternoon light they saw last year. They were looking wonderful until the spots.

We have had a rainier year this season then in summers past. Being in GA that means serious humidity. I believe they had the spots last year, but I thought it was from being too dry. When I saw them again this year on the now healthier plants I knew something was up. I noticed it on the 3 new ones as well. I want to say all at Home Depot had the spots. We had no clue it was a disease or I would have searched for an unaffected plant.

If it is Cercospora... what is the best way to treat/manage it. Thru searching I see it can't be cured, but what can I do to knock it on its butt?

Thank you... Many pics now! :)

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wild_belief(7b)

I think your diagnosis is right. I was talking to Michael Dirr about this yesterday, and he said something about having recently noticed a different kind of fungal leaf spot popping up around the state, but he couldn't remember it by name. In general though, Cercospora is what we get here in GA- and treatment is the same regardless of type.

At our nursery, we try to avoid chemical use whenever possible, so our two main weapons are quarantine and amputation- cut off as much of the affected growth as you can stand, (or as much as you think the plant can stand), remove all fallen leaves from around the base of your shrub, and try to cut down on spread by rinsing your gardening tools in rubbing alcohol when moving from plant to plant.

As far as I know, there are no products that will cure affected foliage, but there are some that can help prevent it from spreading- here's a quote from an article I found on eHow:

"Home gardeners may try applying fungicide products available at nurseries or home improvement stores, such as Cleary's 3336, Zyban or Immunox."

I don't know anything about those products specifically, but I have heard that many of the commercially available fungicides do work fairly well. Cercospora is a real headache, and unfortunately thrives on the same conditions that make for happy hydrangeas, but with some effort, it can be kept to a minimum. Good luck!

    Bookmark   July 30, 2010 at 6:36PM
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redraif(8)

On the pictured plant I guess I'll be doing alot of hacking. How much can it take? You can see that one is quite aweful. Its the worst though.

Thank you for the help

    Bookmark   July 30, 2010 at 7:25PM
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