Any idea what this is on my daylily leaves? It's not rust.

Looks like sunscald to me. Maybe just some old leaves also.I would pluck all the bad looking ones off as near the base of the plant as possible. That will encourage the plant to put out new leaves.

Thanks. We had a wet spring and then hot and dry. It hasn't affected all of them but quite a few.

Same here this year and last. Have it on maybe half my plants. Time to get the scissors out and tidy those up i guess. Grower i know calls it dieback. I would say nothing too serious to worry about.

I have it too, on some plants. Not everything seems to get it - or maybe I am simply turning a blind eye to it on my favorites!

There's a picture of leaf scorch in daylilies here:
http://hyg.ipm.illinois.edu/pa...

To me Ginny's leaf problem looks more like leaf streak:
https://negreenhouseupdate.inf...

Susceptibility to leaf streak varies by cultivar. The leaf streak fungus infects via leaf injury such as mechanical damage or pests but without a microscopic examination it's not possible to be certain that it's leaf streak.

Thanks all. I'll tidy them up and see what happens