Last week the question was: What is this disease growing at the base of this tomato plant?
This is a fungal disease called Southern stem blight (Sclerotium rolfsii). This is the same pathogen that causes white mold in peanuts. It is a soil borne fungus that survives the off season as sclerotia in the soil. It infects tomatoes by growing on the stem right at soil line, causing the stem to decay. Affected plants wilt and die as a result. For more info, take a look at this page.
Here is this week’s question: What are the white things on this strawberry leaf?