Certified GKH Gardening Expert
This appears to be Phytopthora. Here is an article that will explain what it is:
Unfortunately, once established there is going to be a battle to get rid of it. Likely, you will not win this battle.
You can try solarizing the entire area after removing the plants, or you can opt to treat the plants and get what you can from them until they are dead. After this, you will need to attempt to treat the area.
This article will help you with solarizing the area: