What might be causing this?

[Mick]

I don't see any of the little slime trail looking things they leave though, so you're probably right.

 

[Del]

Im up early and as soon as my lights come on I am going to look again. I have 1 microscope and 3 different magnifying loups. I know what insect parts look like under a microscope and so far havent seen anything like that, just these little lesions

 

[umbra]

russets are super small and burrow into the stems and stalks when lights come on, the lesions sound like the burrows they eat into the leaves. But I think you are correct that the flowers are almost ready and it may not matter

 

[Rosebud]

I need a microscope to see russets.

 

[burnin1]

In the past I have seen leaf spot kinda look like that. Even holes in the leaves where the spores were. If you are misting or putting water on the plant in high heat or humid conditions this could happen. If you don't see criiters try a fungicide.