my lobelia is turning brown on part of the plant should I trim the brown part?

Question

Part of plant is nice green and blue flowers. The other half plant is turning brown
What could be wrong.should I trim brown part ?

Answer 1

There could be a few things but I would treat with a fungicide.
Remove the dead parts and dropped leaves and discard.

https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm