Hi Everyone, would really appreciate your help with this. I'm growing cucumbers in a 30 gallon grow bag in zone 9B- Southern California (Pasadena). I started them from seed in plastic cups and then transplanted maybe 1.5 weeks ago. 3-4 days ago I started to notice the stem near the soil thinning and the plant starting to fall over. I've already cut one plant out and now two more are infected. (Pictures included). Based on what I read online, I think it is damping off disease, so I sprayed with hydrogen peroxide solution, then with neem oil solution, and also added cinnamon around the base of each plant. It seemed to work for a few days but this morning I saw another plant wilting.

They seem to be attacking them one at a time.

I've been watering about every 3 days, so I don't think the moisture level or temperature are an issue, as it has been above 60 F here at night and mostly in the 80s during the day.

Could it be a fungus in the mulch? Doesn't seem like insect damage. Would love your expertise as this is my first year growing cucumbers. This one is an Armenian cucumber. I overplanted them to start in case I lost a few. Thank you!

This one is more far gone.

This one I noticed this morning.