Monday, June 17, 2013

Out, Out Damn (Cercospora Leaf) Spot!

A significantly defoliated Oakleaf Hydrangea (following removal of ~80% of foliage apparently infected with Cercospora hydrangeae fungus)

Ugh. Lady Macbeth thought that she had problems.

At least she didn't have to worry (as far as I know) about the fungal pathogen Cercospora hydrangeae disfiguring her oakleaf hydrangea.

I had assumed that hydrangeas were relatively trouble-free and that a native hydrangea like H. quercifolia would be particularly tough and resilient.

But when you assume, you make an ass out of you and me. ("Assume" = "Ass" + "u" + "me")

As it turns out, hydrangeas are susceptible to multiple diseases. Or as University of Georgia says:

[Cercospora] fungal leaf spot can affect most hydrangeas and is generally an aesthetic issue for homeowners. The pathogen will rarely kill the plant, but can reduce plant vigor by defoliation. It is generally more problematic in low maintenance landscape situations or when homeowners overhead irrigate their plants.

Well, if by "low maintenance" they mean gardeners who do not spray fungicides, then I guess I qualify as low maintenance. I expect my plants to take care of themselves. I'll put them in the ground, give them some water to get started, a smidgen of organic fertilizer now and then, accompanied by healthy doses of Encouraging Words, but that's pretty much it. I don't spray for fungus and I don't spray for pests. (Well, I might try to wash off aphids with the garden hose if I'm already giving the plants some water, but that's the extent of it.)

And if by "aesthetic issue" they mean having all the beautiful oakleaf foliage turn spotty and purplish-brown, then yeah, it's an issue.

I appreciate the advice not to irrigate the plants from overhead, but I've hardly been irrigating at all this spring thanks to all this natural irrigation we've been getting from the sky. It's called Rain. And it tends to hit plants from overhead.

So what to do? UGA says the fungus survives in fallen diseased leaves that remain on the ground and ultimately reinfect the plant. It recommends removing dying and diseased leaves to prevent subsequent infections or outbreaks.

So that's what I did early this morning. I went out and removed all the infected leaves I could find, even the ones with just a few visible spots.

Unfortunately that meant that I had to remove about 80% of the foliage.

On the bright side, the remaining foliage should have much better air circulation, which perhaps might prevent a recurrence of the fungus.

What do you think? Have you encountered any fungal problems or other diseases with your hydrangeas? Were you able to overcome those diseases without resorting to fungicidal sprays?

Or did I just site my hydrangea in a bad place - in a corner next to the stairs and crowded up against a camellia and an inkberry holly?

Oakleaf hydrangea "Snowflake" - the one I bought - is supposed to grow 4-6 feet tall and wide. It certainly has the room to grow tall, but it can't really expand to 6-feet wide (maybe not even 4-feet wide) without bumping up against other plants.

And I'm thinking the fungal issues show that Snowflake does not like to be put in a corner. (Just like Baby in Dirty Dancing.)

If today's leaf-pinching doesn't work, I'm thinking I may sadly have to shovel prune the plant this autumn. I'd like to transplant it elsewhere, but apparently it needs at least partial shade and I just don't have any other partially-shady spots where the plant could reach its full-size in an uncrowded setting.

I'm thinking oakleaf hydrangea really needs to be out in the open, perhaps in the shade from some tall trees. (Although apparently it needs moist soil, so these trees couldn't be ones that suck up all the water.) Or all by itself in a wide North-facing border.

Oh and if I do end up removing the oakleaf hydrangea, any suggestions on what I should use to replace it in the semi-shady corner?

I could add another Dixie Wood Fern (I just added one this spring to the corner on the other side of the steps, so adding one on this side of the steps would create a nice symmetry, which my wife especially appreciates in the garden. The fern seems happy on the other side of the steps, but there's more shade over there.)

Or maybe there's some other kind of fern - maybe Christmas Fern?

Other ideas include another Ilex glabra (maybe Shamrock) or another Fothergilla.

Or perhaps another smallish camellia - something like April Dawn.

Thoughts? Experiences? Commiseration? All are welcome!