Question: Why are my tomato plants' leaves turning tan, then brown, from the ground upward?

Answer: Spider mites are almost microscopic pests that show up 2 to 3 weeks after early blight. The leaves turn tan in tiny blotches. As they decline the leaves turn dry and brittle. Watch closely for first evidence. If you want to confirm them, thump a suspect leaf over a sheet of white paper. You'll see dust-sized specks on the paper. If any of them start to walk around, those are the mites. Spider mites are especially threatening to tomatoes as they reach peak productivity in early summer. Apply a specific miticide or general-purpose insecticide to both the top and bottom leaf surfaces.