Hello, all 3 of my hydrangeas that are in pots have this purplish discoloration. When this has happened before I remove the leaves, separate the plants and spray them with Daconil. What is this and am I using the right chemical? Is this a perennial disease because it seems to come up every year? Thank you.

This is a fungal disease called Cercospora Leaf Spot. It is caused by the presence of the fungi as well as by overhead watering in the home or in wholesale nurseries/ local plant nurseries.

Chlorothalonil is an approved substance to control cercospora leaf spot so Daconil is the correct fungicide to use to control it. There is no fungicide that cures this disease so fungicides that control it are simply minimizing the chances of large "displays" of leaf spot... In other words, there is no cure so this only helps keep it in check. The only way to "get rid of it" would be to replace the shrub with another uninfected one.

Cercospora usually appears in the Summer months or at the start of Fall. It is actually present at all times as it resides inside the plant but, it becomes "more" visible after the Summer Solstice, when chlorophyll production tapers off and allows the leaf spots to become more visible. The return of rainfall during the late Summer or early Fall period will determine how much leaf spot there will be in this season: more rain, more leaf spot; less rain, less leaf spot.

It usually does not help much to use fungicides (they help control it, not cure it) so, I use good sanitation practices to prevent the spread. Never water the leaves and instead, water the soil early in the morning (6-8am). Dispose of plant debris -the leaves and blooms- of infected plants in the trash (not compost piles) when these fall down or dry out in the Fall. Use drip irrigation or soaker hoses instead of sprinklers. Increase space between plants so the leaves do not touch. Replace the mulch with new mulch in case of large infestations.

Here is more info:

http://www.aces.edu/pubs/docs/...

You can remove the worst of the infected leaves by cutting off the petiole string that connects the leaf to the stem. Do not cut the end of the stem though as this is where invisible flower buds for Spring 2019 develop in the Summer/Fall months... mid-July where you and I live.

Does that help, Terri?
Luis

@luis_pr

Thank you for taking the time to write such a thorough and clear response to my question. I am very disappointed because all 4 hydrangeas I have are infected. I had purchased 1 hydrangea at home Depot last summer and immediately rooted it into 3 other plants for a total of 4 plants. I planted the main plant that I had purchased and I left the other 3 protected over the Winter to grow in their pots. All 4 have the spots this summer and I am wondering if it's just best to throw them away. The purplish discoloration is so pronounced and ghastly - just awful. I had already thrown away the worst leaves when I found the small one that I used as a picture in this post.

So I guess I will have to be regimented about Spring the hydrangea that is planted. But, when I eventually sell the house I will need to dig up the one that I planted and throw it away as well? Or, should I just dig it up now while it is still small and replace it?

Thank you again for your assistance, I truly appreciate your help. Terri

Maybe not. A rainy season in late Summer or early fall promotes development of the fungi. In those cases, you can expect to see more lesions on leaves. In dry seasons, I see fewer infected leaves. If you sell in a dry late Summer / early Fall, you may not have a big problem. And in a very wet late Summer / early Fall, I would consider applying a fungicide with one of these active ingredients: azoxystrobin, chlorothalonil, mancozeb or thiophanate-methyl. Some fungicide brand names associated with those ingredients are Heritage, Daconil, Dithane, Fore, Protect, Eagle, Immunox, Cleary's 3336 and Halt.

Good sanitation practices such as picking up plant debris, watering only the soil and replacing the mulch has kept my infected hydrangea shrub from passing this issue to other nearby hydrangeas for the last 16 years.

If you sell the house in Spring or early Summer, there may not be lesions visible yet. And none in the winter. But yes, you could also replace the shrub before putting the house for sale. Ironically, the fungi is "all over" the world and you may also find it in your 'new' home. I know, I know, sigh.... ;o)

Luis

Thank you again for your reply. I think I will go ahead and plant them. It seems that replacing them may only end up being a temporary fix. I have several other shrubs that get Daconil showers so I will just add the hydrangeas to the lot. I totally understand the importance of garden sanitation thanks to my roses. Oh my....that's a whole 'nother story.

BTW I purchased a few new hydrangeas for placement at my wood line. Once they are all in bloom I'll send pictures.

"they are all in bloom". Most of the mopheads, lacecaps, serratas and oakleafs here have faded blooms that are turning or have turned all greenish or all brown. Only Annabelle and paniculatas still have "newer" / white-ish blooms. Sigh... one can already read the handwriting on the wall saying that even those blooms will not last far too long. I can't believe half the year has gone by already!