Hi folks
In the last week or two one of my Knockouts, which I planted when I started my garden
18 years ago, just went yellow at the top. The leaves on the top two thirds are just yellow
and fall off when I grab them gently with my hand. Three or four other Knockouts planted
at the same time in the same area of the garden are fine. In fact the bottom of the infected
bush is perfectly green and even the ugly yellow part has a couple of beautiful buds, as
seen in the picture.

Can the experts tell me what's going on?
David
(tearing his leaves...er, hair out)

Is there any chance that this rose may have been hit by frost?

Good thought, Seil, but no chance. We haven't been in the 40s yet in Manhattan. Upstate, yes, but not down here.

Another thought, I'm loathe to do any heavy pruning this late in the season, otherwise I would hack off the top
half of this bush. I think that would not end well.

https://www.gardenguides.com/7...

"Upper Leaves
An iron deficiency is the most likely cause of yellowing upper leaves on a rose bush. It isn't normal for rose bushes to lose their upper leaves because those leaves are newer and still of some use to the plant. If you notice the upper leaves of the bush turning a light green while the veins are remaining dark green, you can take action to prevent them from turning yellow. Treat the plant with iron chelate, which you can purchase at nurseries and garden centers."

I recall you stating a few days ago you watered heavily.
If you don't think you have a drainage problem, I would go with adding a little iron.

Here on Long Island, the temps dropped down to around 46 degrees over the last few nights.

Great, Margie. I've ordered "Grow More" brand iron chelate...my friends at Amazon promised it by Sunday.
I have pretty good drainage. I'll sprinkle the powder on and then water. The water spigots are still working!

Yes, I see the weather report and you usually have lower temps than we do. Here on Eleventh Avenue,
we have a significant urban heat island effect.

Thanks for the help.
David

If you're right in town you probably are warmer because of all the structures around you. But it is possible to have a cold spot as easily as a warm one. I have several different micro climates in my suburban yard.

Yes, and in the city, that's compounded by avenues (north/south) and cross streets (east/west). Next to the river (where I am) the winds in the winter are fierce on bad days. The temps go down to minus digits on a regular basis. Even in the dead of summer there are places in the park across the street, there are lovely shady spots with soft breezes on the hottest of days. All that said, still no frost.