My cherry plant is blooming with flowers, but I'm starting to see that the petals are browning. I'm wondering if this is brown rot? I didn't have any issues last year and I don't remember if this is a normal pollination process (flower drying up). It's been cold and raining, so there haven't been a lot of pollinators, but I've been pollinating with a brush.

Also, how can I know if a cherry flower has been successfully pollinated? Is the stigma supposed to be dark? What part exactly?