Brown Spots on Oregano

I have two varieties of oregano, Greek Oregano and a milder oregano called Wild Marjoram.  As the seasons change in Florida we get more rainfall.  In fact, recently we experienced heavy afternoon thunderstorms for four days in a row.  My balcony is sheltered, but the rain blows in from the east and during rainstorms, my plants get a little wet.

Traditionally oregano dislikes water in the leaves.  Some people will water this plant from the bottom, soaking the pot in water for an hour to avoid getting the leaves wet.  While I avoid wetting the leaves when watering my oregano, I was not able to protect them in the recent storms.   After the storms I noticed that both varieties of oregano developed brown spots.  The Greek Oregano experienced a more dramatic change, entire branches began to dry and turn brown. 

The wild marjoram did not dry up, but did develop brown spots throughout.

There are three possible causes of these brown spots.  The first is a beetle.  The beetle is black with four yellow stripes.  This beetle drinks from the leaves and a brown spot develops from wherever they drank.  I see no evidence of this beetle in my garden.  A second possibility is scorching.  When raindrops fall on the leaves and the sun follows, the raindrops act as a magnifying lens and scorch the leaves.  Sun follows rain frequently in Florida, so this is a possibility.  However when the leaves are scorched, the brown spots are dispersed randomly at different sizes and are not prevalent on every leaf.  The brown spots on my oregano are evenly distributed and are equal in size.  The third possibility is a fungal infection.  When oregano leaves get wet frequently, they are prone to fungal infection.  I believe this is what happened to my oregano.

If you act expediently, you can remove the branches which are infected before it spreads throughout the plant.  If you use this method, be sure to wash your pruning sheers in soap to eliminate the possibility of spreading the fungal infection.  You should also quarantine your infected plants to avoid spreading this fungal infection to other plants.  I discovered and identified the infection only after it had spread throughout the plant.  I believe I am too late to save these oregano plants and I do not want the infection to spread to my other plants.  I have removed these plants and sanitized their pots.