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Hydrangea Cercospora

4 years ago

Hope this makes sense...Just wondering if cercospora is chronic, meaning once a plant is infected it will always come back every year (or multiple times a year) even if you spray for it, or whether once you spray and get it taken care of, it is gone as long as the conditions (heat/humidity) are not a problem.

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Comments (8)

tsugajunkie z5 SE WI ♱
4 years ago
Have you read things like THIS?

tj
luis_pr
4 years ago
last modified: 4 years ago
You cannot cure cercospora yet so, it can come back.

Local end of Summer/Fall weather -if it is very dry- may minimize the number of lesions and help make itself invisible.

Have had it visible for 25+ straight years here. Call it old dependable, hu?

Fungicides only help control it, not cure it, so they are useful when you usually have heavy infestations. Of course, they work best if applied starting around the end of June ish.

Wait for 2 or 3 seasons to get an idea if it becomes visible or not where you live. Use clean sanitation practices to help minimize its re-occurrence.
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Wait, throw diseased material in the trash instead of the compost pile so the spores do not spread elsewhere from the compost pile. You can treat them like a healthy hydrangea but keep the area under/around clean and dispose of the leaves in the Fall by throwing them & the blooms in the trash. Water the soil and not the leaves; always do the waterings eaarly in the mornings. Replace the mulch if it looks like a big infestation. You can cut off the worst leaves or all. There is no telling if the shrubs will quickly/easily recover since they were not established in the garden. Since you got your money back, you could try and not loose anything. The infestation normally develops in late summer and not around this time so most people do not bother to apply fungicides since, by late summer, the leaves are weeks or a few months from drying and falling anyway. But in heavy infestations, fungicides can be applied to treat the condition (but not cure it so it will come back next year) as soon as the spots appear; continue applying until the plant goes dormant. Some fungicides suggested for cercospora (active ingredient name first; commercial name in parenthesis): azoxystrobin (Heritage; smallest application rate and largest repeat interval); chlorothalonil (Daconil); mancozeb (Dithane; Protect; others); myclobutanil (Immunox); thiophanate-methyl (Cleary's 3336).
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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!
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Unless the outbreak is very severe, I would not bother to treat for cercospora in a home garden. This tends to be primarily a nursery issue and most plants in the landscape will outgrow it. Just practice good sanitation and avoid overhead watering. Immunox is registered for this purpose (control of cercospora leaf spot) so I would not see the need to use a copper based fungicide as well. FWIW, I work in a nursery and bring home various unsalable or returned plants and nurse them back to health. Without exception all of those hydrangeas that have been afflicted with cercospora leaf spot show no sign of it the following season. The above plant does look extremely chlorotic (but otherwise relatively healthy) and a fertilizer may be advised. Often, less acidic soils do not allow proper absorption of iron, one of the primary causes of chlorosis, and acid lovers would benefit from chelated iron or a fertilizer for acid loving plants. These typically have iron supplements included. FWIW, sun only until 1:30pm should not be too much, although SC sun is much more intense than mine up here in the PNW. Your plant does not show obvious evidence of scorch and if it is not wilting excessively, it is probably sited OK.
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The spores which cause the leaf spot are your enemy and it sounds like the area where all the affected plants reside is chockful of these spores. This means they are in the leaves, in the stems, in the mulch and so forth. Anything that will make life difficult for the spores will help and based on your comment, a fungicide program may be also required. I would read the information on the link below and then apply these fungicides as described. I would also replace the mulch with new mulch. When spraying, remember to spray the plant leaves' top and bottom as well as the stems. As long as you spray the affected and unaffected plants, cutting the plant down to the ground is not going to do much because the plant will grow anew and get infected from leftover spores in the environment. Consider reviewing just why is the problem so bad. Is the humidity always high in the area of the garden? Or are you maybe watering the soil too much? Etc? High humidity levels are just perfect for the development of the spores so any steps that will reduce the humidity will minimize the problem. As soon as the plants have gone dormant, throw away all the dried out bloomage and leaves in the trash. Then pick up any plant debris that you find and also throw it in the trash. Luis Here is a link that might be useful: Diseases of hydrangeas
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gardengal48 (PNW Z8/9)
4 years ago
And is really only applicable in areas wth high summer heat and humidity. Here, cercospora is pretty much a non-issue. Even overhead watering seems not to encourage it. Rarely does one see it outside of a nursery setting and it will generally disappear once the plant is in the ground

Like with any fungal disease, good garden sanitation will help a lot. Typically spotting will start at the base/oldest foliage first so removal of these affected leaves can help to slow the spread. Pluck off and destroy all the leaves at the end of the season and rake up any fallen ones. Keep a good layer of mulch surrounding the plants to prevent any spores from splashing up. Use drip irrigation or a soaker hose when possible and water infrequently but deeply when you do.
headmotty
Original Author
4 years ago
Thanks all for the answers, but I'm not sure I have the answer I was looking for. So is a cercospora outbreak independent from year to year, where it will only appear if the heat/humidity conditions cause it? Say it appears one year, and either I treat it or not (doesn't really matter for the question), and the leaves fall off for the winter. It won't automatically appear no matter what the following year because the plant "has the disease" will it? It will only appear again if the heat/humidity conditions are again favorable for it, is that right?
luis_pr
4 years ago
last modified: 4 years ago
It is always there because the plant has it. If the climatic conditions where the plant is located are optimal, the leaf spots may be minimized in some years such that you may not notice it. If climatic conditions are not optimal, you may always notice leaf spots. If you want to know whether you have a chance of seeing it, try asking local plant nurseries if customers have complained about cercospora in hydrangeas or ask your agriculture extension service. Or set up an experiment with a hydrangea that has it and see if it gets leaf spots in July-October in the next few years. You may also be able to use a magnifier on leaves after chlorophyll production goes down and see if leaves show the leaf spot. I can "see" the spots sometimes... unaided... in May-July ish or so.... Looks like a green leaf with a spot that has a very slightly different shade of green (darker).
headmotty
Original Author
4 years ago
OK, hey thanks for all the info. Guess I need to watch and hit with fungicide at first signs of appearance.
luis_pr
4 years ago
last modified: 4 years ago
Or make a note in a wall calendar of when you noticed leaf spots and begin applying fungicides a month before that.

I try to control it only using drip irrigation (so no overhead watering of leaves) and clean sanitation practices. Fungicides were more expensive 25 years ago. That is when I moved to my current home and ran into the problem with one hydrangea.

https://ugaurbanag.com/cercospora-leaf-spot-on-hydrangea/
headmotty
Original Author
4 years ago
OK, thanks Luis. I'll be careful with the watering and everything, and see if I can avoid it next year!

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