Lfhaltom
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Hydrangeas lost most of their leaves

I was out of town for a week and came home to find my hydrangeas had lost most of their leaves. When I left they looked perfectly normal. Is this rust fungus or powdery mildew? What do I do? All of the solutions say "when treated in the early stages"
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luis_pr
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Location: Hurst, TX USA Zone 7b/8a

Re: Hydrangeas lost most of their leaves

Hello, Lfhaltom. The fungal infection that you see is called leaf spot or cercospora leaf spot. It is typically caused by overhead watering and the presence of the fungus just about everywhere. The leaf spots tend to become visible once the plants reduce the production of chlorophyll and these spots that were there all along become more apparent. They can be different size: small, medium or large. Large ones may end up "disintegrating" the affected leaf areas and causing holes. The leaf spots take several color tones and look orange-y, brown-ish, purple-ish or black-ish. Sometimes they have a yellow halo.

There are some fungicides that can be used on especially severe cases of infections but be aware that some of these fungicides can be expensive. Their cost needs to be measured against the fact that leaves will not be around much longer once Fall arrives and the leaves dry out when the plants go dormant. Cercospora rarely kills affected shrubs but it surely makes the leaves look ugly. Note that recommended fungicides do not cure the problem; they just help you get it under control. There is no fungicide currently that cures the problem.

In order by their active ingredients, these fungicides are registered for the control of Cercospora leaf spot: azoxystrobin (Heritage; smallest application rate and largest repeat interval); chlorothalonil (Daconil); mancozeb (Dithane; Protect; othrers); myclobutanil (Immunox); thiophanate-methyl (Cleary's 3336). When used, it is best to apply two fungicides with differrent active ingredients per label directions. So, for example, you may apply Fungicide #1 for 9 days, followed by Fungicide #2 for 11 days and back to Fung 1 for 9 days, etc.

The hydrangeas already planted in my current house developed this problem typically in August-ish. To bring it under control, I switched to drip irrigation when my sprinkler in that area broke. I also ceased overhead watering and watered the soil instead. Clean sanitation practices also helped:

Maintaining some distance between plants improves air flow which dries out humidity and makes it uncomfortable for the fungi. Removing dead diseased leaves and plant debris under the plant, applying enough nitrogen to maintain a moderate growth rate, and soil surface watering will help slow the development and spread of Cercospora leaf spot in future years. My plants still have the fungus and I can go outside and find it but it crops up in may be one or two places per infected leaf. In cases of severe infestation, it may be useful to also replace any mulch you have with new mulch as lots of spores may be found also in the mulch (happens more often when infested leaves fall down).

The worst of my affected leaves were cut at the petiole and thrown in the trash. I could have easily thrown away almost all on my first few years but I wanted the plant to have some for photosynthesis. I continued to water at about the same time but only the soil and always early in the mornings. Fallen leaves, dried out leaves (in the Fall), spent blooms and dried out stems contain the fungus so plant debris should be disposed in the trash, not in a compost pile.

Leaf spot may cause some leaves to drop. The lack of moisture and summer sun while you were out possibly caused the loss of many leaves. My sister had a paniculata that was not watered and not well mulched that her husband placed in a bad location. While she went out on a short vacation, it almmost dried out the rootball (your plants look awesome.. very well compared to hers) and the plant is now in the ER. Not sure if you will get any new foliage or if the plant will just keep showing its feet until Spring. If you have a long growing season like I do down in Texas, you might get a few new leaves but probably not many.

Pick up any of the leaves that fell and are still hanging around. Throw them in the trash. Maintain 2-4" of mulch up to the drip line so the moisture does not easily evaporate. Provide about 1.5 gallons of water during the summer (2 or 2+ if you soil is sandy) per plant per watering. If the soil feels almost dry or dry when you insert a finger into the soil to a depth of 4", water the soil from the root ball outwards.

Here is some information about Cercospora Leaf Spot: https://www.aces.edu/pubs/docs/A/ANR-1212/ANR-1212.pdf

Does that help you?
Luis

Lfhaltom
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Re: Hydrangeas lost most of their leaves

Thank you Luis! Yes that was extremely helpful! I was very worried the hydrangeas were going to die but I am so relieved to find out they will be ok! I plan on cleaning the area out today and getting some mulch. Are there any good mulches you recommend?

luis_pr
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Re: Hydrangeas lost most of their leaves

You can use any organic mulch you can find. It is not necessary to use acidic ones, such as pine needles and cypress/etc, as these do not acidify the soil that much, maybe just the top fraction of an inch. In my alkaline soil, I use hardwood mulch or pine bark mulch (medium) from Lowes (whichever is available and-or cheaper). I do not recommend rocks as they absorb heat during the summer days and release it at night; this keeps any plant stressed at night when it should be "recovering". I also saw someone whose Limelight stems -all of them- had fallen to the ground and the shrub had rocks as mulch around it. It happened on a day with no weather to speak of, no deer in the area and no water issues.Or so I was told. We wondered if the rock mulch contributed to the sudden issue with the stems (Limelight is typically a very strong and sturdy bush..... so odd). The rock mulch was new that year but Limelight was not a newly planted shrub.
Last edited by luis_pr on Mon Aug 15, 2016 10:21 am, edited 1 time in total.

Lfhaltom
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Re: Hydrangeas lost most of their leaves

That is very good to know about rocks. We talked about putting rocks around them. I have two dogs that like to dig at the roots of my hydrangeas and lay in the shade. It is extremely aggravating! I have a ton of flower pots surrounding that area so they do not go back there.

luis_pr
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Joined: Sun Jul 05, 2009 12:31 pm
Location: Hurst, TX USA Zone 7b/8a

Re: Hydrangeas lost most of their leaves

I have three pooches and one hydrangea that I was growing died by simply being near Interstate Squirrel. :-() :hehe:

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