Cercospora Leaf Spot

schifferle(5b NE Kansas)February 16, 2010

It's been affecting my Endless Summer hydrangeas (not the Annabelles & Blue Billows), maybe a shrub rose (not entirely sure). The hydrangeas bloom well & appear healthy except for the Cercospora reddish-purple spots. Are there any organic sprays that might help prevent infection? I clean up the infected leaves, don't crowd them, etc., but none of this seems to make any difference. I'd rather not resort to store-bought chemical fungicides if it's avoidable. Because they bloom so well for me, I'd hate to shovel prune them.

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dchall_san_antonio(8 San Antonio)

There are two approaches to organic control of fungus. One is to treat the soil with ordinary corn meal to stop diseases that splash up onto the plant from rain or hard irrigation. The second is to spray with diluted milk on all the surfaces of the plant. Any milk will do.

Corn meal works by increasing the population of a fungus-eating fungus. According to the research at the Texas A&M University back in the 90s, using corn meal will eradicate the disease and restore the soil completely. I would scatter one heaping handful under each plant on a monthly basis. If they are big plants (and I bet they are!!), then I would scatter a heaping handful for every 4 square feet of canopy.

Milk works by...well, we're not sure why it works. The research was done in Brazil and picked up on here by the gardening forums. My guess is milk provides protein, carbohydrates, vitamins, and minerals to the thousands of microbes living on the outside of the plant and those microbes work symbiotically with the plant to protect it. Milk seems to work against the diseases not affected by corn meal. You can dilute it to 3 ounces per gallon of water. Using an adjustable hose end sprayer is the easiest way to apply. Fill the sprayer with undiluted milk, set the dial for 3 ounces per gallon, and spray. Repeat every 2 weeks.

    Bookmark   February 17, 2010 at 10:12AM
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schifferle(5b NE Kansas)

Thank you! Certainly worth a try. I've heard of using milk against Black Spot. Non-fat/skim milk was recommended because of the smell that would develop from the fat content.

    Bookmark   February 17, 2010 at 11:21AM
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dchall_san_antonio(8 San Antonio)

It is not the fat that leads to the smell. It is the decomposition of protein. That gives a sour smell full of ammonia. Unfortunately ammonia is a fertilizer, so you don't want that but you can't avoid it when you spray milk. Outdoors you may not smell it. I used to fertilizer my African violets with milk and I always smelled it.

Non-fat skim is fine, though. Any milk with protein, vitamins, and carbohydrates.

    Bookmark   February 17, 2010 at 12:33PM
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gardengal48

How long have the Endless Summers been planted? Hydrangeas tend to outgrow Cercospora in the landscape but it may take a couple of seasons. And since Cercospora on hydrangeas is only cosmetic in nature (no permanent harm to the plant), I generally recommend no treatment. Mulching well will help to avoid any spores splashing up and reinfecting the foliage. And try to avoid any overhead watering.

Milk won't hurt, though. And many use powdered milk for this purpose.

    Bookmark   February 17, 2010 at 12:50PM
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jean001(z8aPortland, OR)

Also it would be helpful to see images of the problem to verify the diagnosis prior to adding fungicide or other treatment.

Further, as has been stated, one shouldn't spray anything to manage a cosmetic problem.

    Bookmark   February 17, 2010 at 12:56PM
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schifferle(5b NE Kansas)

I'll have to give links to websites that have photos of hydrangeas with this problem. I'm still unfamiliar with how to download photos. The leaves look exactly like these pics. http://plantpathology.uark.edu/3778.htm , http://www.walterreeves.com/qa_display.phtml?qaID=324

I planted them maybe 3 or 4 years ago. They're heavily covered. I wouldn't care if it was a couple spots, but that's not the case. I mulch them every year and don't water overhead. Only nature is watering that way. Organic control was the way I was hoping to go if such a thing was possible for this fungus.

    Bookmark   February 17, 2010 at 4:54PM
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jean001(z8aPortland, OR)

You wrote: "I'll have to give links to websites that have photos of hydrangeas with this problem."

Sorry, but we need images of YOUR plant leaves.

    Bookmark   February 17, 2010 at 7:51PM
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gardengal48

Although I have a LOT of hydrangeas, 'Endless Summer' is not one I grow. But a number of folks have difficulties with this plant (per comments on the Hydrangeas forum) and a search turns up numerous references to this cultivar and Cercospora -- it seems to be heavily prone to this issue, much more so than many other cultivars.

If milk or neem oil (applied early and frequently, before the leaf spot becomes obvious) doesn't keep the problem in check to your satisfaction, I'd consider removing the plants.

    Bookmark   February 18, 2010 at 2:01AM
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schifferle(5b NE Kansas)

gardengal48- Thank you! :-)

jean001- Two problems. As I said, I don't know how to download pics yet and, second, even if I did, February is not a good time for me to get pictures of the leaves. All I could do is show you other hydrangeas where the leaves look EXACTLY like mine. I was trying to get advice before the growing season begins here and I have the problem yet again.

    Bookmark   February 18, 2010 at 8:55AM
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jean001(z8aPortland, OR)

You wrote "February is not a good time for me to get pictures of the leaves"

I fully understand that.

But the problem with people linking to images on the internet that "look the same as my plants" is that the diagnosis is often wrong. Being of suspicious mind, I just want to verify we are talking about the same thing.

    Bookmark   February 19, 2010 at 7:45PM
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schifferle(5b NE Kansas)

jean001, I really need to step up my computer abilities, but the cercospora is rather distinctive with those purple halos. Doesn't look like other hydrangea diseases.

    Bookmark   February 20, 2010 at 1:17PM
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blueheron(z6 PA)

I have a mountain laurel that I planted this spring that has cercospora leaf spot. I have indicated the site.

Penn State recommends chemicals which I don't use, so I'm wondering if the milk or the corn meal will help. I'll try it.

Here is a link that might be useful: cercospora leaf spot

    Bookmark   June 8, 2013 at 8:58PM
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nc_crn

You're better off using a copper based fungicide rather than milk or corn meal...especially corn meal...if you're looking for an organic control.

The emphasis is on "control" not eradication...even the strongest chemicals won't kill it off.

Even still, leaf spot is a hard one to control.

This post was edited by nc-crn on Sat, Jun 8, 13 at 21:16

    Bookmark   June 8, 2013 at 9:09PM
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