I don't grow hostas (too many slugs) but as you say it does look like mould. Are they situated under trees? Some trees attract aphids which excrete honeydew. This drops down onto vegetation below and mould grows on it.

Yes, they are in shade, with the tree canopy probably about 30 feet above. You know, my windshield is covered in tiny drops of something every day from the trees, so maybe this is also dropping down on the hostas.

The funny thing is, these are the only two hostas that seem to have this. There are 5 other hostas in this particular bed, and many others throughout the yard, also in full shade, not to mention 95% of the rest of my garden, but nothing else has these spots.

If this is mold, would it harm the plant?

Dee

I had this problem last year with a couple of hostas growing beneath a spirea infested with aphids. I got rid of the aphids but the sticky honey dew remained on the plants. It sort of washed off over time from rain but it never went away completely. The plants looked dirty all summer, but they came back fine this year.

Karen

Dee, you don't have winter moths do you? In the spring, I've seen black droppings on plants that are under the drip line of the Maples, which will wash off if you get them right away. Just a thought. Now that I look at it, it seems too extensive to be caused by that.

They're pretty expert over on the Hosta forum.

This post was edited by prairiemoon2 on Sat, Jul 12, 14 at 21:29

It does look like droppings of clear honeydew from above. Likely culprits are aphids, scale insects, and tree/plant hoppers. Black sooty mold often begins to grow on that sugary substance.

I'd look UP to find the source of the problem.

It does look like droppings of clear honeydew from above. Likely culprits are aphids, scale insects, and tree/plant hoppers. Black sooty mold often begins to grow on that sugary substance.

I'd look UP to find the source of the problem.

Hmm.... Well, thank you everyone for your input! I really appreciate it. It does look, however, like there's not much I can do about it. My yard is full of large oak trees, so I don't think it's possible to get rid of the aphids completely if they are up in the trees. Kinda gross to think that they are dropping this stuff all over my yard, my cars, and even me, I guess, when I'm out there working, lol!

I'm guessing this won't hurt the plants, although I still wonder why its not on any of the other hostas. Maybe the thick blue leaves show it more than the others...

Thanks again!
Dee

one of the most active forums is the hosta forum ...

the blue glaucous coating on hosta.. is a surface wax ... and such wax can be insulted by many things ..

and stuff that might wash off a non-waxy leaf... gets caught in the wax ...and the leaf is stained for the season ... as the plant can not repair the wax ..

it is cosmetic.. it is not a hosta disease ...

ken