Nasturtium with Black Fly!

15°C  -  10 mph NW Wind Speed  -  16 mph Gusts  -  Cloudy  -  Sunny Spells.  Feeling better, thank goodness.  Visit from sister with Daily Record.  Sat out in porch during a sunny spell  -  blipped a Nasturtium  -  disappointed to see so much Black Flies  -  how can I get rid of them?