Assuming its Leaf Spot how should I treat it? Remove all the infected foliage? Do I need to worry about the cutting leaving the plant open to other infections? Spray it with fungicide?

I've been watering about twice a week, but only when the top 2-3 inches of soil is dry. Drip irrigation, with a dose of Fish Emulsion Fertilizer twice a month. Located in Berkeley, CA and the weather has been mostly dry ranging from 45 nightly lows to 80 highs.

I'm pretty new to gardening, so recommendations for action and products would be greatly appreciated.